Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs - Page 354 - AVS Forum
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post #10591 of 10748 Old 06-26-2014, 12:55 AM
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Quote:
Originally Posted by jim19611961 View Post
I guess I inadvertently found Pandora.
Guess the time has come for you to bite the bullet and learn what FFT is. You don't need to understand the math behind it but the concept. After that things should be much clearer.

There's a German page that tries to explain FFT without math. You might be able to extract helpful information via Google translate:
http://www.sprut.de/electronic/pic/1...sp/fft/fft.htm

Also recommended is this book by Steven Smith which is available for free at:
http://www.dspguide.com/pdfbook.htm

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post #10592 of 10748 Old 06-26-2014, 09:13 AM
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Originally Posted by markus767 View Post
Guess the time has come for you to bite the bullet and learn what FFT is. You don't need to understand the math behind it but the concept. After that things should be much clearer.

There's a German page that tries to explain FFT without math. You might be able to extract helpful information via Google translate:
http://www.sprut.de/electronic/pic/1...sp/fft/fft.htm

Also recommended is this book by Steven Smith which is available for free at:
http://www.dspguide.com/pdfbook.htm
All knowledge is good. I am sure that understanding would broaden my take on why things work the way they do. But for the moment, I am content to realize I can use Spectrograms and Decay to show that data I want to see in a more accurate fashion than Filtered IR's were showing me.

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post #10593 of 10748 Old 06-26-2014, 03:05 PM
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Just an FYI here.

I got a MiniDSP unbalanced/RCA for Father's day. In trying to run the 4 Way Adv plugin I found that I couldn't successfully also use the UMM-6. For whatever reason either my laptop's USB bus or the mic itself would get confused. The mic would not be accessible to either the Sound control panel or REW. To get the mic to work again I'd have to plug the mic into a different computer then back to the laptop after rebooting it. This is an old Mac laptop using Mac OS 10.5.8.

Using two laptops I did all kinds of interesting things with the MiniDSP but I'm not sure I will keep it. I can't tell if it's on and my sub with auto turn on doesn't always turn on with it in the chain.
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post #10594 of 10748 Old 06-26-2014, 03:23 PM
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Interesting, Artur. I experimented with the MiniDSP as well. I found that it reduced the signal level to my subs (Hsu ULS-15's) so that the subs were always going to sleep. I never was able to resolve this behavior so had to switch the subs to "always on".

As for not knowing if the MiniDSP is on or not, if it isn't on, there is no signal to the subs at all. Perhaps I am not understanding what you mean.

Finally, I never had an issue with the mic (a UMIK-1) when using it in conjunction with REW and the MiniDSP. Don't know what is happening there, although I use a Windows laptop, not a Mac.

I finally gave up on the MiniDSP because I never was able to improve upon the bass response that I am getting using Audyssey MultEQ XT32.
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post #10595 of 10748 Old 06-27-2014, 07:50 AM
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Ran across a paper that I found interesting. While much of it I am not sure I agree with, it did mention tolerable distortion figures which not long ago, we were struggling to have some bearing on whats good and not. It also suggests what SPL to measure at.

https://tech.ebu.ch/docs/tech/tech3276.pdf

Harmonic distortion is measured with sinusoidal signals. A constant voltage input signal is supplied to the
loudspeaker. This signal should produce an average sound pressure level of 90 dB in the frequency range from
250 Hz to 2 kHz.


With respect to this level, no harmonic distortion component shall exceed the following values:
–30 dB (3%) for 40 Hz <f< 250 Hz
–40 dB (1%) for 250 Hz <f< 16 kHz

It should be noted that these tests use Sinusoidal Signals. I don't know what that is relative to the sine sweeps most of us use for our measurement data.

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post #10596 of 10748 Old 06-27-2014, 09:00 AM
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This information becomes more useful if we can translate it into a specific procedure in REW, i.e. what signal to output using the Generator, and how to measure and interpret the results. Looking at the Signal Generator, it's not clear which signal to use.
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post #10597 of 10748 Old 06-27-2014, 09:38 AM
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Originally Posted by AustinJerry View Post
This information becomes more useful if we can translate it into a specific procedure in REW, i.e. what signal to output using the Generator, and how to measure and interpret the results. Looking at the Signal Generator, it's not clear which signal to use.
While broadly I agree with you, we only have two signal choices in REW (sine sweep and pink noise?) and hardly anyone uses the pink noise. Yes, the paper is vague about the details on how to measure, other than SPL which is specified. But interpretation it seems to me is fairly straightforward.

I don't think there is enough based on this one paper to include an entry in the REW guide, but it does add to what we knew before in terms of acceptable distortion figures at different frequency ranges.

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post #10598 of 10748 Old 06-27-2014, 09:45 AM
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Originally Posted by jim19611961 View Post
hardly anyone uses the pink noise.
I do! Great way to gather spatially averaged data for LF EQ.

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"In science, contrary evidence causes one to question a theory. In religion, contrary evidence causes one to question the evidence." - Floyd Toole
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post #10599 of 10748 Old 06-27-2014, 09:49 AM
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Originally Posted by markus767 View Post
I do! Great way to gather spatially averaged data for LF EQ.
A contrarian lurks in any broadly stated opinion

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post #10600 of 10748 Old 06-27-2014, 10:16 AM
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I think everyone would agree that less distortion is better when reproducing a source signal. Contrarians? Whether any individual can hear it or not at any particular level or frequency is no different than the way we interpret and use the measurements for anything else with REW. Some choose to be more picky, and some are more of the "it's a helluva lot better than it was before" and "that's the most treatment I can get away with/fit in/afford" variety.

I don't really think "the guide" needs to be updated re this, beyond just a small note that the facility exists, to be used for edification/curiosity or perhaps choosing between config options that otherwise seem very similar by other measurements. Distortion measurements can also potentially indicate gear deterioration if collected over time, or perhaps mismatched components, or maybe even point to the next upgrade (i.e. another sub).
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post #10601 of 10748 Old 06-27-2014, 10:28 AM
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I think adding something on how to measure it and what it means would be a useful addition (ie use a sweep not any sort of use, be aware that distortion varies with SPL). I think you could add some commentary around interpreting the results too. The only unknown as far as I can see is what a good number is, it is easy to say what a bad number is though.
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post #10602 of 10748 Old 06-27-2014, 10:30 AM
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Contrarians?
I was merely teasing Marcus.

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post #10603 of 10748 Old 06-27-2014, 10:38 AM
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^ I know. I just wanted to get a response from a contrarian who thought more (source reproduction) distortion was desirable, for my amusement.
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post #10604 of 10748 Old 06-27-2014, 10:39 AM
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Lots of people like the increased distortion provided by most tube amps.

Selden
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post #10605 of 10748 Old 06-27-2014, 10:41 AM
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I think adding something on how to measure it and what it means would be a useful addition (ie use a sweep not any sort of use, be aware that distortion varies with SPL). I think you could add some commentary around interpreting the results too. The only unknown as far as I can see is what a good number is, it is easy to say what a bad number is though.
I have heard the 1% figure through the midrange (250hz) and up being the threshold for audible detection for a long time. The paper I quoted seems to agree with that. IMO, that is the upper limit of acceptability. 1/2 that figure I would call good, and 1/3 that figure excellent.

Perhaps the same can be said for the 3% figure quoted for below 250hz. 1/2 that being good, 1/3 of that being excellent.

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post #10606 of 10748 Old 06-27-2014, 10:43 AM
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Originally Posted by Selden Ball View Post
Lots of people like the increased distortion provided by most tube amps.
Even ordered distortion, yes.(2nd, 4th, 6th, ect... harmonics)

For the record, I used to be among those people. Now, not so much.

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post #10607 of 10748 Old 06-27-2014, 10:50 AM
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Originally Posted by 3ll3d00d View Post
I think adding something on how to measure it and what it means would be a useful addition (ie use a sweep not any sort of use, be aware that distortion varies with SPL). I think you could add some commentary around interpreting the results too. The only unknown as far as I can see is what a good number is, it is easy to say what a bad number is though.
A good number is zero. A less good number is more than zero. What constitutes a bad number is highly controversial. I know you know this isn't like decay time and such, where we can't absolutely say what the optimal time is, so we need a guide for reasonable desirable goals. But I think it's safe to say what the obvious goal is for distortion, and my point was we don't really need a guideline for "the goal". Yes, a guideline for the distortion-measuring SPL is reasonable. I think a reasonable measuring SPL is what I usually listen at, and another measuring SPL at how loud I'm likely to ever listen. But the latter is potentially "dangerous" and that's kind of what I meant by distortion graphs can indicate "mismatching" or gear unsuitability for the desired goal. Better to know than not know, but not good to destroy finding out...
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post #10608 of 10748 Old 06-27-2014, 11:00 AM
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A good number is zero. A less good number is more than zero. What constitutes a bad number is highly controversial. I know you know this isn't like decay time and such, where we can't absolutely say what the desirable time is, so we need a guide for reasonable goals. But I think it's safe to say what the obvious goal is for distortion, and my point was we don't really need a guideline for "the goal". Yes, a guideline for the distortion-measuring SPL is reasonable. I think a reasonable measuring SPL is what I usually listen at, and another measuring SPL at how loud I'm likely to listen. But the latter is potentially "dangerous" and that's kind of what I meant by distortion graphs can indicate "mismatching" or gear unsuitability for the desired goal. Better to know than not know, but not good to destroy finding out...
I think the idea here is to say where red flags are in a given measurement. If you are reading 3% THD in the midrange, or 10% in the bass, that is a red flag, IMO. How good 0.8% is in some specific sense is certainly controversial and shouldn't be pinned down with a specific judgement.

Same said for a FR that is +/-12db at 1/12 octave smoothing. A red flag. Or a decay that takes over a second to be -20db down.

I think what many of us do a good deal of the time is take our measurements and look to see if anything is out of whack. Not only does the guide tell you how to take a measurement properly, but it should steer you to what constitutes red flags for each measurement.

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post #10609 of 10748 Old 06-27-2014, 11:03 AM
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Originally Posted by Selden Ball View Post
Lots of people like the increased distortion provided by most tube amps.
Yes some do, but they typically do not admit that it's distortion per se. The same people typically also pooh-pooh measurements, and would be unlikely to be in an REW thread unless reformed, since it's all about "sounding good" (and unadmitted "audiophile cred"). [I did not forget about those people, I also have several tube amps, including some SET ones.] That said, many types of tube amps don't distort as much as many cheap SS AVR amps do, and tube amps "pack it in" much more gracefully and with less-damaging consequences than SS amps.

Personally, I can very easily see having quality tube amps for everything, except SS for the sub amps (I don't like tube amp bass in a home environment). But my room is already hot enough, and I don't have the space for tube power amps anymore.
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post #10610 of 10748 Old 06-27-2014, 11:19 AM
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I think I see better now where you guys are coming from re a note/guideline in Jerry's guide. To me it was a matter of "informed" personal discretion, and interest, so it seemed there was not much to say. But I can see it now from Jerry's POV, in that if he says just about anything, it potentially opens up a can of worms. IOW may do more harm than good, in a "beginners" guide.
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post #10611 of 10748 Old 06-27-2014, 11:30 AM
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Well 0 is an impossible goal but otherwise I agree with both of you I don't advocate a beginners guide that tells people how to fry their ears and kit, I do think that telling people how to measure it and that this is important is a good thing.
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post #10612 of 10748 Old 06-27-2014, 11:38 AM
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I needed to remeasure/reconfigure because one of my subwoofer amps is non-functional. I was hoping the minidsp would fill the gap but I wasn't happy with it. So, back to adjusting by hand.

This time around I decided to target distortion sacrificing some volume. What would have been helpful was knowing how much incremental distortion is audible. For example, the FR variance outside of +/- 3db is said to be audible. What variance +/- distortion % is audible?

Following graphs have no EQ, not smoothed.

Here's the old.


Here's the new.


At that room mode I got the distortion from 12.7% to 3.6%. Worse distortion over the range went from 31%@20Hz to 4.6%@33Hz.

Qualitively, at the low end I hear more detail. Using Ella Fitzgerald's Fascinating Rhythm the bass line is quite a bit more focused/precise.

Nothing necessarily louder. There's no more low end oomph but what low end is there is noticeably crisper.

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Attached Images
File Type: jpg old distortion.jpg (73.1 KB, 129 views)
File Type: jpg new distortion.jpg (73.9 KB, 129 views)
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post #10613 of 10748 Old 06-27-2014, 11:50 AM
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As far I know the actual audibility/impact of distortion is content dependent so I am not sure that is a question that can be answered authoritatively. Nevertheless I would say that (30%) is a clear sign you are beyond the limits of your setup.
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post #10614 of 10748 Old 06-27-2014, 11:53 AM
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Quote:
Originally Posted by artur9 View Post
I needed to remeasure/reconfigure because one of my subwoofer amps is non-functional. I was hoping the minidsp would fill the gap but I wasn't happy with it. So, back to adjusting by hand.

This time around I decided to target distortion sacrificing some volume. What would have been helpful was knowing how much incremental distortion is audible. For example, the FR variance outside of +/- 3db is said to be audible. What variance +/- distortion % is audible?

Following graphs have no EQ, not smoothed.

Here's the old.


Here's the new.


At that room mode I got the distortion from 12.7% to 3.6%. Worse distortion over the range went from 31%@20Hz to 4.6%@33Hz.

Qualitively, at the low end I hear more detail. Using Ella Fitzgerald's Fascinating Rhythm the bass line is quite a bit more focused/precise.

Nothing necessarily louder. There's no more low end oomph but what low end is there is noticeably crisper.

P.S. The new avs image feature sux.
I like the direction your going here

As far as what variance of distortion is audible, well, that, among other topics, is one we are trying to nail down. But I would like to add an illustration from outside the box on distortion by giving an analogy.

In my system, I have spent much time getting late reflections back to the listening position. How I would describe there effect is that I don't really hear them, but I notice when they are not there. With distortion, I think a similar analogy holds. You might say you cant hear 10% distortion in your bass region, but the better question might be, if it were 1% instead, would you notice the difference?

In your case, it would seem the answer is yes.

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post #10615 of 10748 Old 06-27-2014, 12:44 PM
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Quote:
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As far I know the actual audibility/impact of distortion is content dependent so I am not sure that is a question that can be answered authoritatively.
How so? Rock vs classical? Electronic vs acoustic? Or ... ?
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post #10616 of 10748 Old 06-27-2014, 01:07 PM
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You might say you cant hear 10% distortion in your bass region, but the better question might be, if it were 1% instead, would you notice the difference?

In your case, it would seem the answer is yes.
That is exactly how I always say it. Most people have not had the opportunity to hear the lower bass regions at low distortion levels. I would even hazard (not much hazard...) that 10% is actually quite low a comparative level (to 1%, say) if you examine the typical mass-market offerings.

artur9: By content dependent I'm pretty sure he meant things like you're going to be a lot fussier about bass distortion if you listen to a lot of Stanley Clarke (say) vs '60s psychedelic rock (say). What is this "classical" you speak of? Buddy Holly, Elvis?
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post #10617 of 10748 Old 06-27-2014, 02:14 PM
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What is this "classical" you speak of? Buddy Holly, Elvis?
Anything my daughter won't let me listen to. Elvis is definitely included on the verboten list. Pre-Elvis almost certainly.

But, seriously, I'm wishing I had more Baroque music.
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post #10618 of 10748 Old 06-27-2014, 02:27 PM
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I like the direction your going here
Thanks! Also, would like to emphasize/show gratitude for how much the guidance of this group has really helped me improve things over the last few months (or longer). The music sounds so much better that it's difficult to tear myself away. The clarity for movie watching has really made that activity much more enjoyable as well, although that's just a side effect for me.

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As far as what variance of distortion is audible, well, that, among other topics, is one we are trying to nail down.


While I was doing this, I was trading off slight FR flatness for less slight distortion improvements. Knowing that I couldn't hear variations within 2-3 db helped tilt some of the adjustments. But it was a constant fiddling trying to minimize both.

Some guidance on what threshold(s) would be very helpful. I know we don't have that yet. I'm no golden ear so I have to do it by the numbers. I personally would definitely recommend 5% rather than 30%.
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post #10619 of 10748 Old 06-27-2014, 02:50 PM
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Some guidance on what threshold(s) would be very helpful. I know we don't have that yet. I'm no golden ear so I have to do it by the numbers. I personally would definitely recommend 5% rather than 30%.
And we may never have it. You mentioned FR deviation +/-3db as an accepted deviation. +/-3db @ 1/3 oct smoothing is a completely different criteria than +/- 3db @ 1/24 oct smoothing. So which did you mean? Which one is the one most people achieve in there own system? Meant rhetorically, what I am really getting at is these standards, while have some across the board consensus, are mainly personal in the sense that if it sounds good to you and your at +/-3db at 1/12 oct smoothing, then your going to say thats good enough. If your distortion figures at 40hz are 3%, and it sounds good to you, your going to say that is good enough. On the other hand, if you are already below 1%, end to end, 3% is going to sound unacceptable. And so on.

Lets face it, we are all selfish in that at the end of the day, we are really only concerned with what our own system sounds like. And we are only impressed by those measurement criteria that surpass our own, regardless of the claims made by others as to how they say it sounds. I dont mean this to sound ugly, but it is human nature.

A Mustang seems fast until you ride in a Turbo Carrera

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post #10620 of 10748 Old 06-27-2014, 03:05 PM
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And we may never have it. You mentioned FR deviation +/-3db as an accepted deviation. +/-3db @ 1/3 oct smoothing is a completely different criteria than +/- 3db @ 1/24 oct smoothing. So which did you mean?
A Mustang seems fast until you ride in a Turbo Carrera
Strictly as a datapoint I was going by unsmoothed because I was working with the frequencies for which the guide states that to be preferable. Smoothing probably would have made it easier.

Car-wise, I'll take whichever does the hairpin quicker
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