Spectrum Labs - different slope than room/subwoofer frequency sweeps - AVS Forum
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post #1 of 41 Old 08-22-2013, 11:24 AM - Thread Starter
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I started this discussion in MKTheater's new IB build thread, but thought it best to post in its own thread.

Spectrum Labs is an FFT analyzer that displays equal energy at all frequencies. It will show white noise as flat and pink noise as falling off at 3 dB per octave as you go up in frequency.

rosa-blanco-rojo_fft_pink_white.gif

Room measurement software such as REW or Omnimic; RTA's (Real Time Analizers); and professional audio software such as Avid Pro Tools, WaveLab, Cubase, or Abelton Live display equal energy based on octave. They will show pink noise as flat and white noise as increasing 3 dB per octave as you go up in frequency.

rosa-blanco-rojo_rta_pink_white.gif

Because Spectrum Labs has a different slope than other measurements you can't directly compare the charts to room measurements or subwoofer measurements such as those on data-bass.com. In order to directly compare, the Spectrum Lab chart has to be rotated. Here is an example of The Incredible Hulk as posted on the forum at data-bass.com:



Here it is tilted 3 dB per octave to represent how it will show when measured in-room using REW or Omnimic:



Here is The Dark Knight Rises tilted. You can see that it should be down in-room by almost 10 dB at 20 Hz vs 40 Hz.



Spectrum Lab is accurately measuring and displaying the audio content. However, the graphical representation is different than that used by most other audio tools/methods.

This has several implications
When rotated to match room/subwoofer response graphs, the Spectrum Labs graphs show that
  1. bass output peaks somewhere in the 40-50 Hz region and flattens or rolls off as you go down in frequency
  2. subwoofers with limiters can still accurately produce most of the recorded bass without have a "variable frequency response" since the tilted Spectrum Lab graphs match very well with a lot of the subwoofer measurements at data-bass.com - even at higher output levels.
  3. ported subwoofers are producing more of the original bass than thought which corresponds with most listener impressions at subwoofer GTG's
  4. studios are viewing a different representation of the audio than what Spectrum Labs presents

Here is some pertinent info from Sweetwater.com:
Quote:
Pink noise versus white noise. “And in this corner…”

“Is pink noise the appropriate filtered noise for all sound system setups? If white noise is equal energy at all frequencies shouldn’t that be a better reference signal for testing PA & studio speakers? Even if pink noise is actually white noise filtered to approximate the human ear’s frequency response, shouldn’t the systems be tested with white noise? After all, a human mix engineer will mix to a human ear’s frequency response, right?”
My favorite thing is when people ask the same question three different ways trying to make a point. Well, I guess that’s not really my favorite thing, but I do enjoy it.

A lot of people are confused about the difference between pink and white noise. Pink noise is the right type of noise to use to calibrate audio equipment (at least if you are using it for equalization calibration). Here’s where everyone gets confused:

White noise is equal energy per frequency and pink noise is equal energy per octave. Now, think about how we perceive sound. Think about what an octave is to us. Other than the pitches involved we don’t hear anything more substantial happening when a high note jumps up an octave than we do a low note. It’s the same number of frets on a guitar, or keys on a keyboard either way. But in terms of the actual frequencies being produced the difference is great.

Here’s an example. The difference between 100 Hz and 200 Hz is one octave. The difference between 5 kHz and 10 kHz is also one octave. However, in terms of frequencies the difference between 100 Hz and 200 Hz is only 100 Hz, whereas the difference between 5,000 Hz and 10,000 Hz is 5,000 Hz. The relative relationship is the same, but the actual difference mathematically is quite substantial. With white noise there is a ton more energy in-between 5 kHz and 10 kHz compared to between 100 Hz and 200 Hz because it spans a wider range of frequencies and they all contribute to the overall level per octave. The whole point of pink noise is to distribute the energy according to how we hear. So the pink noise energy between 100 Hz and 200 Hz is the same as between 5,000 Hz and 10,000 Hz. Equal energy per octave.

So it’s not that pink noise is calibrated to the human ear’s frequency response per se. It’s just calibrated to how we hear, which is very well grounded in math. Each time the frequency doubles we hear that as an octave. From one octave to the next we expect to hear an appropriate amount of sound energy (depending upon the program material), which is why we calibrate our audio systems to pink noise.

We’ve done several Tech Tips about how to calibrate your system with noise and an RTA in the past, so feel free to consult the archives for more detail. At a practical level, this means you can run pink noise through your system and set your overall EQ so you get a flat line on a typical RTA display. A flat line would signify equal energy at every octave. Some audio engineers feel that this can produce an unnaturally “bright” sounding system and do an additional rolloff of 3 dB per octave above 4 kHz or so. Or they may just do one 3dB rolloff at some frequency and leave it at that. The specific techniques vary, but the perceived need for it has more to do with the dispersion characteristics of the equipment involved, the measurement accuracy, and personal tastes than anything. Your actual mileage will probably vary.
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post #2 of 41 Old 08-22-2013, 11:38 AM
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Very interesting. I suspect this will end up being a really long thread.
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post #3 of 41 Old 08-22-2013, 12:33 PM
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post #4 of 41 Old 08-22-2013, 01:53 PM
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I disagree. There is no such thing as calibration for pink noise vs white noise in a measurement system. The measurement is either accurate or it is not accurate.

The intensity seen in <20 Hz bandwidth is all about time, not pink noise. A logarithmic sine sweep spends the same time sweeping from 3-6 Hz as it does sweeping from 60-120 Hz. More time per frequency.

Depending on the settings you choose for SL, you can have more accuracy or less accuracy down low, but you'll still see about a -10dB drop fro 0-120 Hz with a log sweep, more or less, depending on the accuracy of the settings for that bandwidth.

A linear sine sweep spends equal time on each frequency. Run one through SL and there will be no roll off.

Play a 10 Hz sine wave into SL, then an equal intensity sine wave at 100 Hz. They will show the exact same color intensity and waveform amplitude graph.

Fortunately, movie sound effects aren't logarithmic sine sweeps. smile.gif

Sound is not mixed flat regarding the low end... ever. The re-recording engineers have the equal loudness curves built into their ears and automatically bump the low end to match our hearing. They are more or less capable in that regard as they are more or less faithful to the sound designer's effects creation, thus our 1-5 star ratings.

Low end effects can be centered at any frequency the sound designer chooses. The re-recordist may bump, pull down or filter that effect at his/her will if no one in post production objects. SL shows us what was done in the final analysis, more accurately than any other free program I'm aware of, but of course, I'm always open to suggestions in that arena.
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post #5 of 41 Old 08-22-2013, 06:14 PM
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Yeah, I'm kinda lost here as to what this means.

If a play 5, 20 40, 80Hz burst tones encoded at -20dB on Soho54's Test DVD, this is what I get:



All at the same level.

And so if I play back this scene from How to Train Your Dragon digitally, this is the peak hold that is recorded:



Spectrum Lab:



If I play back those same burst tones through an actual sub system, they should be all at the same level (provided your system is capable with a flat response).

So if that's true, then your peak reproduction of that HTTYD scene will look like the log above.

Why wouldn't it?
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post #6 of 41 Old 08-23-2013, 08:19 AM - Thread Starter
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I'll repeat what I said in my first post: Spectrum Labs is accurately measuring and displaying the audio content. I am in no way saying it isn't.

When you look at subwoofer maximum SPL charts, one will see measurements taken at 1M and measurements taken at 2M. If someone wants to compare measurements taken at 1M with measurements taken at 2M they adjust one of the measurements by 3 dB. The measurements are both accurate, but an adjustment needs to be made for comparison.

I'm saying the same thing is true with Spectrum Labs (or any FFT analyzer) vs a logarithmic measurement display. Both are accurate, but when you compare the charts of one system vs another you need to tilt the graphs by 3 dB for an apples to apples comparison.

I first started thinking about this when using soho54's Test DVD. Back on June 30, 2011 I posted the following chart in the New Master List of BASS in Movies with Frequency Charts thread:

attachment.php?attachmentid=216455&d=1309458023

I later realized I the FFT analyzer was displaying the sine waves with a flat power spectral density and that I could also display them in a logarithmic power spectral density.

Here is are tones from 3-100 Hz showing with a flat (linear) power spectral density:


Here are the same tones switched to show a logarithmic power spectral density:


Both graphs are of the same content, but display it differently.

Room Equalization Wizard (REW) and Omnimic both use logarithmic sine sweeps. You can read about logarithmic sine sweeps in the Transfer-Function Measurement with Sweeps paper by Swen Müller and Paulo Massarani. It says on page 35 (formulas removed):
Quote:
Sweeps can be created either directly in the time domain or indirectly in the frequency
domain. In the latter case, their magnitude and group delay are synthesized and the
sweep is obtained via IFFT of this artificial spectrum. Some of the formulas given here
are written differently from the typical mathematical standards, but their form is suitable
for direct implementation in software.
The two most commonly known types are the linear and the logarithmic sweep. The
linear sweep has a white spectrum and increases with fixed rate [Hz] per time unit:

Japanese scientists [35, 36] have been using linear sweeps for good reasons long before
the MLS technology got popular in acoustics. They refer to the linear sweep as “time
stretched pulse” (TSP), but of course any broad-band excitation signal, be it a sweep or
a noise signal, could be considered a pulse whose energy has been spread out in time.
In the last years, the originally white “TSP” has been improved for use in acoustics by
giving it pre-emphasis at lower frequencies [37]. Also known are bandpass-filtered
sweeps for specific purposes [38].

Logarithmic sweeps have a pink spectrum, meaning their amplitude decreases with
3 dB/octave. This also means that every octave contains the same energy. The
frequency increases with a fixed fraction of an octave per time unit.

On page 3:
Quote:
The FFT spectrum of such a logarithmic sweep
declines by 3 dB/octave. Every octave shares the same energy, but this energy spreads
out over an increasing bandwidth. Therefore the magnitude of each frequency
component decreases. We will later see that this excitation signal, which has already
been in use for such a long time, has some unique properties that keep it attractive for
use in the digital word of today. One of these properties is that the spectral distribution
is often quite well adapted to the ambient noise, resulting also in a good SNR at the
critical low end of the frequency scale.

So, both REW and Omnimic display their logarithmic sine sweeps flat while an FFT displays them as declining by 3 dB/Octave. This is verified by performing a sine sweep with REW and then using its RTA to also measure the Periodic Pink Noise played through your system that can be created using the Generator in REW. Both will display the same transfer function. However, the same Periodic Pink Noise played through an FFT analyzer will decline by 3 dB/Octave.

Nfraso, all of your charts can be accurately compared since they all use an FFT analyzer.
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post #7 of 41 Old 08-23-2013, 08:57 AM - Thread Starter
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Don Keele's Development of Test Signals for the EIA-426-B Loudspeaker Power is the basis for test signals in the CEA-2010-A standard used by data-bass.com for subwoofer measurements. In the paper Keele shows the difference between displaying band limited and shaped noise using an FFT spectrum (linear power spectral density) and a 1/3rd octave spectrum (logarithmic power spectral density):





Both are displaying the same data, but do so differently. The 1/3rd octave spectrum is the method of displaying data used in subwoofer and speaker frequency response charts.

In order to make an FFT spectrum match a 1/3rd octave spectrum, the graph must be tilted by 3 dB/octave or you are not making a direct comparison!
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post #8 of 41 Old 08-23-2013, 10:21 AM
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Quote:
Originally Posted by desertdome View Post

I'll repeat what I said in my first post: Spectrum Labs is accurately measuring and displaying the audio content.
The power density of a broadband constant voltage signal drops by 3dB per octave with increased frequency. That's why pink noise is used to measure speakers, and it does result in a flat chart . White noise played through a flat system will show rising sensitivity at 3dB per octave with increasing frequency.
To confirm this, do an SPL sweep using pink noise, then do a manual plot using a sine wave tone with constant voltage. They'll be the same.

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post #9 of 41 Old 08-24-2013, 10:32 AM
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Quote:
Originally Posted by desertdome View Post

I started this discussion in MKTheater's new IB build thread, but thought it best to post in its own thread.

Spectrum Labs is an FFT analyzer that displays equal energy at all frequencies. It will show white noise as flat and pink noise as falling off at 3 dB per octave as you go up in frequency.

rosa-blanco-rojo_fft_pink_white.gif

Room measurement software such as REW or Omnimic; RTA's (Real Time Analizers); and professional audio software such as Avid Pro Tools, WaveLab, Cubase, or Abelton Live display equal energy based on octave. They will show pink noise as flat and white noise as increasing 3 dB per octave as you go up in frequency.

rosa-blanco-rojo_rta_pink_white.gif

While all of the above is true, the next part of the post is where the train leaves the track:


Quote:
Originally Posted by desertdome View Post

IBecause Spectrum Labs has a different slope than other measurements you can't directly compare the charts to room measurements or subwoofer measurements such as those on data-bass.com. In order to directly compare, the Spectrum Lab chart has to be rotated. Here is an example of The Incredible Hulk as posted on the forum at data-bass.com:



Here it is tilted 3 dB per octave to represent how it will show when measured in-room using REW or Omnimic:


Let's add another version of the same graph. This one shows the 100 Phon Equal Loudness Curve overlaid onto the graph:



All movies with bass will adhere closely to the ELC, save for the roll off that some post production folks may choose to employ, unless, that is, they were mixed by this guy:


Quote:
Originally Posted by desertdome View Post

Spectrum Lab is accurately measuring and displaying the audio content. However, the graphical representation is different than that used by most other audio tools/methods.

This has several implications
When rotated to match room/subwoofer response graphs, the Spectrum Labs graphs show that
  1. bass output peaks somewhere in the 40-50 Hz region and flattens or rolls off as you go down in frequency

It DOES?:



Quote:
Originally Posted by desertdome View Post

[*] subwoofers with limiters can still accurately produce most of the recorded bass without have a "variable frequency response" since the tilted Spectrum Lab graphs match very well with a lot of the subwoofer measurements at data-bass.com - even at higher output levels.

THIS^^^ you'll have to prove. No way I agree with the assertion and no way it's true. wink.gif
Quote:
Originally Posted by desertdome View Post

[*]ported subwoofers are producing more of the original bass than thought which corresponds with most listener impressions at subwoofer GTG's

Yeah, this one ^^^ as well is not gonna happen. To date, GTG impressions are so flawed I can't believe anyone would reference them in a serious discussion regarding accurate reproduction of soundtrack content.

Please conduct this simple test as part of the GTG:

Create a digitally fed SpecLab cap of Irene from BHD, then mic each of the subs @ the GTG reproduction of the same scene at the LP with your 'flat to 1 Hz' rig at 0dBRL. These graphs are relevant to each other, leaving the apples/oranges argument out of the equation. They'll show which sub(s), if any are accurately reproducing the content. Without that data, impressions are irrelevant. If you can show that all of the subs are accurately reproducing the content of films like HTTYD, WOTW. B:LA, Total Recall, etc., then the impressions will be much more useable and your claims will carry more weight.

Again, I only take issue with the suggestion that SL graphs can't be compared to in-room FR graphs. I do it all the time and have for many years. They correlate exactly and they don't need to be tilted. And, the idea that limiters, filters and resonant systems have no bearing on accuracy of reproduction is like saying black looks exactly like white if you tilt your head and squint. tongue.gif
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post #10 of 41 Old 08-25-2013, 06:28 PM
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Quote:
Originally Posted by Bill Fitzmaurice View Post

Quote:
Originally Posted by desertdome View Post

I'll repeat what I said in my first post: Spectrum Labs is accurately measuring and displaying the audio content.
The power density of a broadband constant voltage signal drops by 3dB per octave with increased frequency. That's why pink noise is used to measure speakers, and it does result in a flat chart . White noise played through a flat system will show rising sensitivity at 3dB per octave with increasing frequency.
To confirm this, do an SPL sweep using pink noise, then do a manual plot using a sine wave tone with constant voltage. They'll be the same.




Desertdome is talking about the difference observed between an FFT measurement and an RTA measurement when a broadband signal is being used as a signal.

What is an SPL sweep that uses pink noise? Pink noise is pink noise and no frequency sweep is available / needed. White noise is white noise and no frequency sweep is available / needed. A frequency sweep can be either linear, log, or measured with the REW signal generator.
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post #11 of 41 Old 08-25-2013, 06:32 PM
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Quote:
Originally Posted by bossobass View Post

I disagree. There is no such thing as calibration for pink noise vs white noise in a measurement system. The measurement is either accurate or it is not accurate.



There is such a thing as calibration that produces a flat frequency response with the use of pink noise verses white noise in a measurement system.
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post #12 of 41 Old 08-25-2013, 08:35 PM
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Quote:
Originally Posted by J_Palmer_Cass View Post

There is such a thing as calibration that produces a flat frequency response with the use of pink noise verses white noise in a measurement system.

Example?
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post #13 of 41 Old 08-27-2013, 04:34 PM - Thread Starter
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Quote:
Originally Posted by bossobass View Post

While all of the above is true, the next part of the post is where the train leaves the track:
Let's add another version of the same graph. This one shows the 100 Phon Equal Loudness Curve overlaid onto the graph:



All movies with bass will adhere closely to the ELC, save for the roll off that some post production folks may choose to employ, unless, that is, they were mixed by this guy:

The overlay of the 100 Phon ELC over the Spectrum Labs graphs is a perfect illustration of the problem. The Peak Hold graph is based on a linear power spectral density and the ELC graph is based on a logarithmic power spectral density. The ELC graph indicates it is based on logarithmic power because of the Sound Pressure Level shown in dB on the left side. Sound Pressure Level is measured in logarithmic power. One cannot overlay the graphs without adjusting the slope! An incorrect assumption about the graphs is leading to errors in conclusions.

Instead of focusing on a small portion of the ELC, here is the full bandwidth ELC:



You can see that at 100 Hz vs 500 Hz the 100 Phon has a 5 dB difference.

In Spectrum Lab, expand the frequency out to 500 Hz and the amplitude to 125 dB. The maximum output from 100 Hz to 500 Hz drops way off.

A clip from Skyfall (all channels and full bandwidth):



Pink Noise for reference:



If the ELC graph was using the same slope as the Spectrum Labs graph, then you wouldn't see the decay in output in Spectrum Labs as you go up in frequency. A wider bandwidth comparison between Spectrum Labs and the ELC graphs also indicate that each are using a different slope to their graphs. One of the graphs has to be changed in order to accurately compare the two.

Comparison of Spectrum Labs vs Subwoofer Peak Output when Spectrum Labs graphs are converted to the same visual scale:
Here is the War of the Worlds peak output graph. I don't know why a linear frequency axis is used since most frequency graphs are logarithmic. You can change it to log in Spectrum Labs under the Spectrum (2) tab.



I have imported the graph into REW and then changed it from linear power (blue) to logarithmic power density (red). I also changed the frequency axis to logarithmic (each octave approx. the same width).



Here is the SVS PB13 Ultra 20Hz tune maximum output from Data-bass.com. I show both the actual measurement (green) and adjusted for room gain per the Bossobass graph (red).



Bossobass's room gain profiles chart:



Now let's compare apples to apples by overlaying the PB13 with room gain over the logarithmic War of the Worlds graph:



This illustrates that you can play War of the Worlds at 118 dB from 12.5 Hz and up and track completely with the maximum output of the signal from 14Hz and up.
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post #14 of 41 Old 08-28-2013, 03:00 PM
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So that $5k I threw into 4 sealed UXL18 sub system was a waste and I should have just bought those dual powered Caps? GRUMBLE
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post #15 of 41 Old 08-28-2013, 04:32 PM
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What about below 14hz? We know excellent ported subs can get most of the bass, we want all of it.
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post #16 of 41 Old 08-28-2013, 05:00 PM
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DD,

What am I gonna do with you? biggrin.gif:eek:

So, is pink noise down 3dB/octave on a SL waterfall graph or is it down -50dB/octave as your posted graph shows? And, dunno what scene you capped but the 500 Hz content in that scene is obviously non-existent. No calibration you could dream up will put the content down -120dB and still call it content.

I did not say SpecLab is calibrated to ELC, I said that all mixers have ELC built in to their hearing, thus the low end mix will be reflected in the SL caps... which it is.

You imported the PH graph into REW and "I also changed the frequency axis to logarithmic (each octave approx. the same width)." That's ALL you did. The graph is identical otherwise. Distorting the graph to "logarithmic power density" assumes anyone would believe there is higher SPL content at 160 Hz in WOTW than there is at 30 Hz. Good luck with that suggestion.

BTW, with the settings used in that SL cap, full bandwidth waterfalls aren't possible.

Please do this:

Play a 10 Hz sine tone through the REW tone generator into SL. Next, repeat the process with a 100 Hz sine tone and then repeat once more with a 500 Hz sine tone and post the SL graph. Then explain why those equal level sine tones all show exactly the same level in SL, but a movie soundtrack cap needs to be tilted?

Now, on to this absurd idea that a PB13 can accurately reproduce WOTW at 118dB in-room or on any planet in this universe...

You post Josh's max compression sweep trace, add my room gain profile data and wham, WOTW at reference level (from 14 Hz up). biggrin.gif

You forgot to include some data in that wet dream:

First there's this little snag when pushing the Ultra that hard:



What's the distortion level below tune at that level? We can't say... it's off the chart. But, we can say it's very high and certainly audible.

What happens below 10 Hz? We can't say, there's no data because there was no input signal, much less a complex signal spanning 5 octaves.

And how closely does a max output sine sweep or a tone burst at any point in the bandwidth equate in maximum output to an infinite spread of -5dBFS simultaneous frequencies across 5 octaves? Well, we do have some data to venture a guess:



There are only 10 frequencies in this "effect" and they range from 92dB-102dB, yet they sum to 110dB and create all sorts of squiggly things above the noise floor.

Casting no aspersion on John's efforts, peaks are tricky things to measure accurately. You assume the maximum peak in WOTW is 115dB and you assume that 115dB is the only requirement from the sub at 2 meters distance with room gain to accurately reproduce the soundtrack at your seat and you assume that a sine sweep accurately approximates the extremely wide bandwidth and infinite frequency effects found in WOTW.

If you prefer to lop off 2-1/2 octaves of WOTW, tilt it's graph and fantasize about a PB 13 providing accurate reproduction at the seats, be my guest. You won't be alone in that fantasy around here. For myself, I'm gonna hafta pass on that one due to overwhelming evidence to the contrary. smile.gif
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post #17 of 41 Old 08-29-2013, 08:13 AM
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Quote:
Originally Posted by bossobass View Post

DD,

What am I gonna do with you? biggrin.gif:eek:

So, is pink noise down 3dB/octave on a SL waterfall graph or is it down -50dB/octave as your posted graph shows? And, dunno what scene you capped but the 500 Hz content in that scene is obviously non-existent. No calibration you could dream up will put the content down -120dB and still call it content.

I did not say SpecLab is calibrated to ELC, I said that all mixers have ELC built in to their hearing, thus the low end mix will be reflected in the SL caps... which it is.

You imported the PH graph into REW and "I also changed the frequency axis to logarithmic (each octave approx. the same width)." That's ALL you did. The graph is identical otherwise. Distorting the graph to "logarithmic power density" assumes anyone would believe there is higher SPL content at 160 Hz in WOTW than there is at 30 Hz. Good luck with that suggestion.

BTW, with the settings used in that SL cap, full bandwidth waterfalls aren't possible.

Please do this:

Play a 10 Hz sine tone through the REW tone generator into SL. Next, repeat the process with a 100 Hz sine tone and then repeat once more with a 500 Hz sine tone and post the SL graph. Then explain why those equal level sine tones all show exactly the same level in SL, but a movie soundtrack cap needs to be tilted?



One must note that SL graphs do not represent SPL levels nor do they represent the way that you hear. Hearing is octave based, and the SL display is not octave based. ELC does not apply to the to the SL display the way that you indicate that it does. Linear or log scale, SL still does not display content that appproximates the way that we hear.

Pink noise is a wide band test noise that approximates a noise distribution in the manner that we hear (octave based). If you use a standard sine wave test tone (assume all levels at -20 dBFS) of 1 kHz and compare it to a 10 Hz sine wave test tone, they both will be shown as -20 dBFS on a calibrated SL display. However, pink noise does not a have a linear noise distribution. Pink noise will give you a 10 dB per decade rolloff on the SL display (or any FFT display).

If you ever looked at a wideband movie soundtrack on SL you would easily notice that 10 dB per decade rolloff on a movie soundtrack. You do notice the 20 dB rolloff of audio content from 1 to 100 Hz on the SL display, but you say that is caused by ELC.



Shown below is a SL chart that displays white noise. Short bursts of white noise with various time increments. Lower group is the Bosso smeared settings, and the upper group uses faster speed wider bandwidth FFT settings.

The upper spectrogram shows pink noise as a "reference curve" that slopes at 10 dB per decade (white reference trace). White noise shows as "measures flat" in the upper spectrogram.


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post #18 of 41 Old 08-29-2013, 09:37 AM - Thread Starter
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Originally Posted by bossobass View Post

DD,

What am I gonna do with you? biggrin.gif:eek:

So, is pink noise down 3dB/octave on a SL waterfall graph or is it down -50dB/octave as your posted graph shows? And, dunno what scene you capped but the 500 Hz content in that scene is obviously non-existent. No calibration you could dream up will put the content down -120dB and still call it content.

Could you (or someone else) please post a Spectrum Lab graph extended to 500 Hz. I use Windows 7 and have used both yours and maxmercy's Speclab settings files.
Quote:
You imported the PH graph into REW and "I also changed the frequency axis to logarithmic (each octave approx. the same width)." That's ALL you did. The graph is identical otherwise. Distorting the graph to "logarithmic power density" assumes anyone would believe there is higher SPL content at 160 Hz in WOTW than there is at 30 Hz. Good luck with that suggestion.
SPL is measured in 1/3 octave bandwidths. The 20-40 Hz octave is louder than the 80-160 Hz octave. I don't see the problem.

There is no distorting of the graph to logarithmic power density. One must change the slope of the Spectrum Lab graph to match the SPL charts. Is it "distorting the graph" to change a 2M max output SPL number to a 1M max output SPL number? No, it is necessary for an accurate comparison. Here is War of the Worlds max output represented in an SPL chart (note: max SPL on a dbfs chart don't equate max SPL so you can't determine max SPL from the chart):


Quote:
You forgot to include some data in that wet dream:

First there's this little snag when pushing the Ultra that hard:



What's the distortion level below tune at that level? We can't say... it's off the chart. But, we can say it's very high and certainly audible.
You're little snag is forgetting about room gain. So you're saying that room gain also increases distortion? That's ridiculous. According to your own room gain profiles chart a subwoofer has between 8-15 dB of gain at 15 Hz. This means that if you are playing at 115 dB you will have under 10% THD down to at least 15 Hz per Ricci's own chart. Due to room gain, when you get below 30 Hz you need to switch to the 110 dB THD sweep and below 20 Hz you need to switch to the 105 dB THD sweep.
Quote:
You assume the maximum peak in WOTW is 115dB and you assume that 115dB is the only requirement from the sub at 2 meters distance with room gain to accurately reproduce the soundtrack at your seat and you assume that a sine sweep accurately approximates the extremely wide bandwidth and infinite frequency effects found in WOTW.
You are right that I shouldn't assume the maximum peak in WOWT is 115dB. A dbfs peak and an SPL peak are not equal. That is why dbfs peaks shown in Spectrum Labs don't represent the actual SPL peaks. I was stating that, based on the maximum SPL chart for the PB13 Ultra 15 Hz tune, one can play War of the Worlds at up to 118 dB (in the bass) from 2 meters with room gain.
Quote:
If you prefer to lop off 2-1/2 octaves of WOTW, tilt it's graph and fantasize about a PB 13 providing accurate reproduction at the seats, be my guest. You won't be alone in that fantasy around here. For myself, I'm gonna hafta pass on that one due to overwhelming evidence to the contrary. smile.gif
Your overwhelming evidence is all based on an improper understanding of how FFT graphs represent the sound and how that translates at the seat to SPL output.

J_Palmer_Cass understands perfectly! cool.gif
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post #19 of 41 Old 08-29-2013, 09:38 AM
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Quote:
Originally Posted by desertdome View Post

[*]ported subwoofers are producing more of the original bass than thought which corresponds with most listener impressions at subwoofer GTG's

Interesting thread. I've observed this too. In multiple meets the deepest bass notes clips often tend to be subjectively rated higher on subs that by measurements aren't even be producing those ultra low frequencies.

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Originally Posted by HuskerOmaha View Post

So that $5k I threw into 4 sealed UXL18 sub system was a waste and I should have just bought those dual powered Caps? GRUMBLE

lol....

still a pot stirrer eh?

you mean your questioning whether or not you should have bought these subs?
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Originally Posted by HuskerOmaha View Post

I can’t wait to eat crow.

Guesses (in order of my fake confidence): 1) HSU, 2) Cap Pro

Sub B: [revealed to be Cap Pros]
This thing dominated music. I really hope it isn’t the Cap Pros because I’m going to be the butt of jokes and feeling stupid for months until Archaea forgets I say this (he won’t). These were BY FAR the best to me for music. Destroyed the music. Perfect. Articulate. Fun. Of course I think they are sealed, because sealed subs are the BEST FOR MUSIC, right? Man, I hope I’m right on at least that. Did I mention these absolutely "beast mode" the music?

Oh and to prevent your rebuttal --- in case you forgot --- the bass you heard missing in BHD later in that quoted post was because the Inuke DSP 3000 amp actually shut off/overloaded/power cycled during Cap's audtion. That was one of four times the Inuke power cycled during the cap pair's movie demos. The process only takes seconds, but of course it occured on the specific timepoints of the most demanding movie clips in the Hulk, HTTYD, BHD, and we think U-571. The subjective comments for the caps jived with the known power cycle times precisely. I still wish we had a Crown XLS-5000 or a couple of Jeff's speaker power amps driving the caps that day - maybe you would have crowned it King for movies as well. ;p

I miss you man - when are you hosting your next Omaha meet?

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post #20 of 41 Old 08-29-2013, 10:00 AM - Thread Starter
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Quote:
Originally Posted by J_Palmer_Cass View Post

Shown below is a SL chart that displays white noise. Short bursts of white noise with various time increments. Lower group is the Bosso smeared settings, and the upper group uses faster speed wider bandwidth FFT settings.

The upper spectrogram shows pink noise as a "reference curve" that slopes at 10 dB per decade. White noise shows as "measures flat" in the upper spectrogram.
Thanks for the graph. It really helps illustrate the problem presented by using SL charts to try to represent how bass is produced in-room.

As I mentioned in my first post, studios calibrate with pink noise, not white noise. FilmMixer has stated that the frequency response in their rooms is calibrated with pink noise. Maxmercy sent me two links explaining how theaters calibrate using pink noise. Meyers Sound has an article explaining how pink noise is used in calibrating cinema sound systems.
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Ported subs without HP filters will reproduce the low stuff, but it is high THD so yeah, you feel lots of stuff, just not the fundamental.

I have listened to many subs and every single ported or horn sub did sound like it had more low end than even multiple sealed 18's, why? Because unless they have boost they will naturally be way down in spl to whatever tune the ported sub goes. My DTS-10's kicked some serious butt in my room and they were flat to 10hz in my room with no EQ(ULF's, not upper bass). It kicked the crap out of my eD 190v2 system which I thought would have all the low stuff because it was sealed and plenty of displacement. It lost and lost bad, I could not believe it and sold my awesome sub system for these two horn subs. I then bought a CHT system and the same thing happened, the DTS-10's reigned supreme and I did not know why accept this time I knew about natural rolloff of different subs and sealed subs. The horns were already boosted down low due to design. I needed to boost the crap out the sealed subs below 20hz to equal the rolloff of the DTS-10's and once I did that any advantage was now in favor of the sealed subs! I happen to have enough displacement, power, and a room to do this. My eD 13Av2's had even less rolloff and with little boost was even better! Again, until one really makes there system flat to 3-5hz their sealed system will sound like a ported system down low, actually with less tactile feel because the ported system without a HP will produce lots of extra harmonics that makes things seem more powerful. Try some sweeps and compression testing and you will see. Once that compression starts to kick in the THD starts to rise, and fast. When I measured my F-20's they did great to 10hz during a response but when measured for THD they could only muster 110 dBs at 10hz at 10% THD and the sealed system hit 120 dBs! huge difference although the 20hz stuff was very close. The F-20's were awesome but I missed all that low end the DTS-10's and boosted sealed systems provide. I have the room to really feel the low stuff but it is not shake but extra pressure and other feelings.
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post #22 of 41 Old 08-29-2013, 11:14 AM
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Quote:
Originally Posted by Archaea View Post

Interesting thread. I've observed this too. In multiple meets the deepest bass notes clips often tend to be subjectively rated higher on subs that by measurements aren't even be producing those ultra low frequencies.
lol....

still a pot stirrer eh?

you mean your questioning whether or not you should have bought these subs?
Oh and to prevent your rebuttal --- in case you forgot --- the bass you heard missing in BHD later in that quoted post was because the Inuke DSP 3000 amp actually shut off/overloaded/power cycled during Cap's audtion. That was one of four times the Inuke power cycled during the cap pair's movie demos. The process only takes seconds, but of course it occured on the specific timepoints of the most demanding movie clips in the Hulk, HTTYD, BHD, and we think U-571. The subjective comments for the caps jived with the known power cycle times precisely. I still wish we had a Crown XLS-5000 or a couple of Jeff's speaker power amps driving the caps that day - maybe you would have crowned it King for movies as well. ;p

I miss you man - when are you hosting your next Omaha meet?

Probably selling house in spring so we'd have to plan that soon. Heck depending on how this goes I may have to sell my subs to rkinmoval and do Caps since I won't be doing a dedicated room.

Then again, I'm pretty stubborn. My father in law told me I'd be stupid to not own a minivan, so naturally ill be getting a Suburban.

I'm not sure I could live with the defeat of acknowledging you may be right. smile.gif

I think DD raises great points that I haven't seen discussed in this direction before. I may start to think filmmixer isn't crazy.
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post #23 of 41 Old 08-29-2013, 11:43 AM - Thread Starter
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Quote:
Originally Posted by Bossobass 
Distorting the graph to "logarithmic power density" assumes anyone would believe there is higher SPL content at 160 Hz in WOTW than there is at 30 Hz.
So you are saying that when Don Keele shows his test signal in an FFT spectrum and then on a logarithmic power density spectrum that he is distorting the graph? He is showing the exact same data using two different methods.




Quote:
Originally Posted by Archaea View Post

Oh and to prevent your rebuttal --- in case you forgot --- the bass you heard missing in BHD later in that quoted post was because the Inuke DSP 3000 amp actually shut off/overloaded/power cycled during Cap's audtion. That was one of four times the Inuke power cycled during the cap pair's movie demos. The process only takes seconds, but of course it occured on the specific timepoints of the most demanding movie clips in the Hulk, HTTYD, BHD, and we think U-571. The subjective comments for the caps jived with the known power cycle times precisely. I still wish we had a Crown XLS-5000 or a couple of Jeff's speaker power amps driving the caps that day - maybe you would have crowned it King for movies as well. ;p

Why did the amp shut down during these demanding clips? It is probably assumed that is happened because of the wider bandwidth bass. This can contribute, but Mark Seaton showed how my amp could shut down with a 20 Hz HPF at HuskerOmaha's subwoofer GTG. The CAP drivers probably have a high impedance in the 30-50 Hz range. This creates a high voltage requirement and the amp can't provide enough voltage. Bill Fitzmaurice helped me understand this with this comment:
Quote:
Originally Posted by Bill Fitzmaurice 
That would explain it. Bridging isn't about power, it's about doubling voltage swing into a high impedance load that the amp would not otherwise be able to drive to its thermal or displacement limit, whichever is lower. I'd say you don't have that problem. The only safe way to bridge is if you have a limiter to prevent excess voltage swing.
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post #24 of 41 Old 08-29-2013, 02:36 PM
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Quote:
Originally Posted by desertdome View Post

Why did the amp shut down during these demanding clips? It is probably assumed that is happened because of the wider bandwidth bass. This can contribute, but Mark Seaton showed how my amp could shut down with a 20 Hz HPF at HuskerOmaha's subwoofer GTG. The CAP drivers probably have a high impedance in the 30-50 Hz range. This creates a high voltage requirement and the amp can't provide enough voltage. Bill Fitzmaurice helped me understand this with this comment:
Quote:
Originally Posted by Bill Fitzmaurice 
That would explain it. Bridging isn't about power, it's about doubling voltage swing into a high impedance load that the amp would not otherwise be able to drive to its thermal or displacement limit, whichever is lower. I'd say you don't have that problem. The only safe way to bridge is if you have a limiter to prevent excess voltage swing.

The amplifiers in question shut down from over-current conditions, not clipped Voltage limits.

I haven't had time to look through all of this, but it looks like there's some combined confusion of different measurement methods, tools, related stimulus signals and the way they are displayed and averaged.

As an example, the sweep used in TDS measurements such as with my TEF25 are in fact a linear sweep. Related to what bosso mentioned, but more specifically, the time and frequency windowing (if any) of different measurements will determine what stimulus produces what result. Some playing around with loop back signals would probably help with some understanding a bit.

As an example, an RTA's sampling can be perfectly and equally filled with the correct pink noise stimulus resulting in a flat response. A straight FFT of the same signal should show the -3dB/octave slope to the spectral content... I believe some of the confusion comes from the fact that most systems use a dual FFT process which looks at the *difference* between the stimulus and the measured response, hence pink noise can be used as there is energy to perform the comparison at all frequencies and it's easier on the tweeters and tester's ears. By comparison, if I ran a TDS sweep while a loud pink noise signal was playing and disconnected the drive signal, I would again see the sweep's sampling of the -3dB/oct spectral content.

Maybe someone can ping bwaslo to comment further.

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post #25 of 41 Old 08-29-2013, 03:15 PM - Thread Starter
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Quote:
Originally Posted by Mark Seaton View Post

The amplifiers in question shut down from over-current conditions, not clipped Voltage limits.
Thanks for clarifying.
Quote:
As an example, an RTA's sampling can be perfectly and equally filled with the correct pink noise stimulus resulting in a flat response. A straight FFT of the same signal should show the -3dB/octave slope to the spectral content...
Yes, and I'm trying to explain that Spectrum Lab is an FFT spectrum analyzer.
Quote:
I believe some of the confusion comes from the fact that most systems use a dual FFT process which looks at the *difference* between the stimulus and the measured response, hence pink noise can be used as there is energy to perform the comparison at all frequencies and it's easier on the tweeters and tester's ears. By comparison, if I ran a TDS sweep while a loud pink noise signal was playing and disconnected the drive signal, I would again see the sweep's sampling of the -3dB/oct spectral content.

Maybe someone can ping bwaslo to comment further.

I mentioned in a previous post that measurement systems use logarithmic sine sweeps. You can read about logarithmic sine sweeps in the Transfer-Function Measurement with Sweeps paper by Swen Müller and Paulo Massarani. This paper is referenced by the REW user manual as the basis for how it performs sweeps. I've used REW and Omnimic in the same rooms with the same results so I assumed Omnimic also uses logarithmic sine sweeps. TDS sweeps are discussed in the paper and it mentions that they are linear. This correlates with your comment.
Quote:
There are a number of drawbacks associated with TDS measurements. The most serious
is the fact that TDS uses linear sweeps and hence a white excitation spectrum. In most
measurement setups, this will lead to SNR at low frequencies. If the whole audio range
from 20 Hz to 20 kHz is swept through in 1 second, then the subwoofer range up to
100 Hz will only receive energy within 4 ms. This most often is insufficient in a
frequency region where the output of a loudspeaker decreases while ambient noise
increases. To overcome the poor spectral energy distribution, the sweep must be made
very long or the measurement split into two ranges (for example one below and one
above 500 Hz). Both methods extend the measurement time far beyond of what would
be needed physically to perform a measurement of the particular spectral resolution.
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post #26 of 41 Old 08-29-2013, 07:25 PM
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Fellas, this is a circle jerk if I've ever been in the middle of one. rolleyes.gif

We don't use SL to measure logarithmic sine sweeps. They are irrelevant to the discussion so please stop holding them up as evidence against the facts of the matter.

Pink noise is simply white noise run through a 3dB/octave filter. Yes, we get that. Please, no need to repeat it 100 more times.

Once again for DD and JPC:

1) Use the REW generator to play a 10 Hz sine wave signal into SL.

2) Use the same REW generator to play a 100 Hz sine wave signal into SL.

3) Use the same REW generator to play a 500 Hz sine wave signal into SL.

Display the SL waterfall of the above exercise.

Explain why the colors match exactly, then explain how graphing a soundtrack is any different.

OK, here, I'll do it for you:



The tones are of equal level when input into SL, therefore SL renders them as such. There is zero difference when sending the 1-120 Hz content of the SW output jack into SL. It renders that content by input level per frequency. When you input the content into SL by mic'ing the subwoofer system, you will see a accurate depiction of the subwoofer systems distortion of that content.

Pink noise and white noise are irrelevant. Keele's shaped noise burst is irrelevant.

Please set up an accurate mic and run it into SL and show me the ported sub with no distortion at 118dB or whatever you're trying to convince me of. I deal in evidence, not jargon that sounds cool.



I don't see a 3dB/octave roll off in this scene, do you?

Why is it rolled off above 80 Hz? Because Dolby suggests LFE be mixed that way. Begin to roll off @ 80 Hz so that you don't run into the brick wall @ 120 Hz. Yes, I know the filter can be defeated, etc., blah, but the point is that most vets still do it that way. That doesn't mean there are no scenes with higher levels at 120 Hz that at 40 Hz, it's just that those are not the scenes we graph. I mean, really, this whole discussion is as Mark correctly identified it; a bunch of confusion stirred in out of context.
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post #27 of 41 Old 08-29-2013, 11:14 PM
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Quote:
Originally Posted by bossobass View Post




I don't see a 3dB/octave roll off in this scene, do you?

Why is it rolled off above 80 Hz? Because Dolby suggests LFE be mixed that way. Begin to roll off @ 80 Hz so that you don't run into the brick wall @ 120 Hz. Yes, I know the filter can be defeated, etc., blah, but the point is that most vets still do it that way. That doesn't mean there are no scenes with higher levels at 120 Hz that at 40 Hz, it's just that those are not the scenes we graph. I mean, really, this whole discussion is as Mark correctly identified it; a bunch of confusion stirred in out of context.



You have to use the peak and average chart to see the 10 dB per decade rolloff of the FTT spectum in a typical movie sound track. Samples below are taken from the first 7 minutes of Casino Royale.



Spectrumlab - linear FFT set to display in log scale. Pink noise shows a 10 dB per decade roll off. The white line is a reference pink noise curve as shown on the SL FFT peak and average chart.

Both the peak and average curves of the Casino Royale sample show a 10 dB per decade roll off.






TrueRTA - Octave based display. Pink noise measures as flat.

The peak RTA chart shows a relatively flat curve for the Casino Royale content.






Both charts are accurate and they both originate from identical content.
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post #28 of 41 Old 08-30-2013, 08:38 AM
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Quote:
Originally Posted by J_Palmer_Cass View Post


Both charts are accurate and they both originate from identical content.

Correct...

+1 to Mark's post.

The point DD is trying to make is that since the peak and average traces in SL are linear based while most measurements of the response of subs are typically log sine based, that making direct data comparisons of spectral weight/balance of content in movies captured in SL to response charts of subwoofers will be skewed somewhat if the differences in the way the data is presented are not accounted for. Both are accurate but the presentation is different.

In the case of Bosso or anyone else for that matter using SL to capture movie signals direct and then setting up a mic and capturing the reproduction by the system, both are taking place in SL so that is perfectly valid since the comparison is of how close the system matches the electrical signal.
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post #29 of 41 Old 08-30-2013, 10:13 AM - Thread Starter
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Quote:
Originally Posted by bossobass View Post

We don't use SL to measure logarithmic sine sweeps. They are irrelevant to the discussion so please stop holding them up as evidence against the facts of the matter.
Except that frequency response graphs produced by REW, Omnimic, ARTA, CLIO, and HOLMImpulse use logarithmic sine sweeps. What is irrelevant then is using Spectrum Lab graphs in a direct comparison to their frequency response graphs.

Quote:
Originally Posted by J_Palmer_Cass View Post

You have to use the peak and average chart to see the 10 dB per decade rolloff of the FTT spectum in a typical movie sound track. Samples below are taken from the first 7 minutes of Casino Royale.
Great job! Are those taken with a loopback like Mark suggested? Loopback vs direct from file don't really matter, but I'm curious.

Quote:
Originally Posted by Ricci View Post

The point DD is trying to make is that since the peak and average traces in SL are linear based while most measurements of the response of subs are typically log sine based, that making direct data comparisons of spectral weight/balance of content in movies captured in SL to response charts of subwoofers will be skewed somewhat if the differences in the way the data is presented are not accounted for. Both are accurate but the presentation is different.
Exactly what I'm saying!

When maximum output is measured in program that uses a linear power spectrum (such as Spectrum Lab) is directly compared to a frequency response graph, this is what is represented using the max ouput chart from Skyfall:



When maximum output is measured in a program that uses a logarithmic power spectrum (such as TrueRTA or REW), this is what is represented:



The second chart provides an apples to apples comparison with the measurements at data-bass.com. When you put the subwoofer in a room and experience room gain, then this is possible:



I mentioned before that there are several implications when one converts a linear power spectrum graph so that it can be directly compared to a logarithmic power spectrum graph.
  1. In-room bass output peaks somewhere in the 40-50 Hz region and flattens or rolls off as you go down in frequency
  2. Subwoofers with limiters can still accurately produce most of the recorded bass without having a "variable frequency response" since the logarithmic maximum output graphs match very well with a lot of the subwoofer measurements at data-bass.com - even at higher output levels.
  3. Ported subwoofers are producing more of the original bass than thought which corresponds with most listener impressions at subwoofer GTG's.
  4. Studios are viewing a different representation of the audio than what Spectrum Labs presents
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post #30 of 41 Old 08-30-2013, 11:18 AM
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Can someone pass the lotion? I find this thread very interesting. eek.gif

I think these are some good points brought up that i haven't seen before. Thanks DD. smile.gif
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