noob TRUE/FALSE question about sub 20Hz - AVS Forum
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post #1 of 16 Old 10-06-2012, 08:41 AM - Thread Starter
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TRUE or FALSE: my new NAD T 777 will clip anything below 20Hz, so my expensive subwoofer will not produce < 20Hz audio when attached to the NAD.

so you don't have to look it up, this is the data on the NAD T 777:
Amplifier Section Frequency Response ±0.8dB (ref. 1kHz, 20Hz-20kHz)
Preamplifier Section Frequency Response ±0.5dB (ref. 20Hz-20kHz)

very much appreciate answers to my naive question.
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post #2 of 16 Old 10-06-2012, 09:04 AM
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False. Look up the specs for any AVR, amp, or preamp and you're likely to see the same "20 - 20 KHz" range. That's the standard range used when measuring distortion figures or the flatness of the response curve, eg. +/- 0.8 dB. Your receiver will send the sub all the low frequencies that are encoded on the disc, so no worries...
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post #3 of 16 Old 10-06-2012, 09:10 AM - Thread Starter
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ah. okay, so the spec sheet is just saying that within a certain range of dB it won't send < 20Hz, but it will send signal < 20Hz.

that makes sense. thank you!
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post #4 of 16 Old 10-06-2012, 09:21 AM
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The preamp may be just as flat down to 10 Hz, but one can't tell from the manufacturer's specs. It's probably very good however.
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post #5 of 16 Old 10-06-2012, 02:13 PM
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IIRC, the "20Hz-20KHz" spec deals only with the speaker channels, and has nothing to do with the LFE channel (0-120Hz) or the Subwoofer output.
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post #6 of 16 Old 10-07-2012, 02:50 AM
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Quote:
Originally Posted by prefetch View Post

TRUE or FALSE: my new NAD T 777 will clip anything below 20Hz, so my expensive subwoofer will not produce < 20Hz audio when attached to the NAD.

so you don't have to look it up, this is the data on the NAD T 777:
Amplifier Section Frequency Response ±0.8dB (ref. 1kHz, 20Hz-20kHz)
Preamplifier Section Frequency Response ±0.5dB (ref. 20Hz-20kHz)
very much appreciate answers to my naive question.

The spec does not say how the device performs above 20KHz or below 20 Hz. So you cannot, by definition, tell from the spec what power the device will make at any given frequency below 20 Hz or above 20KHz before "clipping," however one defines it (is it one percent distortion" a tenth of a percent" ten percent?) You'd need to see testing at whatever frequency you think is relevant to know the answer.

Car analogies are awvul, but a spec of 0 to 60 Mph in 6 seconds does not mean a car won't go faster than 60.
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post #7 of 16 Old 10-07-2012, 08:17 AM
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Quote:
Originally Posted by prefetch View Post

TRUE or FALSE: my new NAD T 777 will clip anything below 20Hz, so my expensive subwoofer will not produce < 20Hz audio when attached to the NAD.

so you don't have to look it up, this is the data on the NAD T 777:
Amplifier Section Frequency Response ±0.8dB (ref. 1kHz, 20Hz-20kHz)
Preamplifier Section Frequency Response ±0.5dB (ref. 20Hz-20kHz)
very much appreciate answers to my naive question.
As others have said, you can't tell anything about the response below 20 Hz from those spec's. However, there is another way to "know" the response below 20 Hz. Your receiver is Dolby TrueHD and DTS-MA capable. The spec's for those formats REQUIRE response to 3 Hz from the subwoofer output. So you can rest assured that your receiver will definitely not "clip anything below 20 Hz." It will definitely send sub-20 Hz content to the subwoofer.

Craig

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post #8 of 16 Old 10-07-2012, 08:30 AM
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Quote:
Originally Posted by craig john View Post

Your receiver is Dolby TrueHD and DTS-MA capable. The spec's for those formats REQUIRE response to 3 Hz from the subwoofer output.

Super informative, thank you smile.gif

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post #9 of 16 Old 10-07-2012, 01:50 PM
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Quote:
Originally Posted by craig john View Post

As others have said, you can't tell anything about the response below 20 Hz from those spec's. However, there is another way to "know" the response below 20 Hz. Your receiver is Dolby TrueHD and DTS-MA capable. The spec's for those formats REQUIRE response to 3 Hz from the subwoofer output. So you can rest assured that your receiver will definitely not "clip anything below 20 Hz." It will definitely send sub-20 Hz content to the subwoofer.
Craig

This. I didn't focus on the fact the questio relates to the sub out, not the receiver's amp performance.

To the OP "clip" in the amplifier context means "distort" not "roll off" as I think you may have had in mind, and as you move along in your audio learning curve using the terms the way folks in the business use them will make it much easier to communicate.
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post #10 of 16 Old 10-08-2012, 07:47 AM
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Quote:
Originally Posted by craig john View Post

As others have said, you can't tell anything about the response below 20 Hz from those spec's. However, there is another way to "know" the response below 20 Hz. Your receiver is Dolby TrueHD and DTS-MA capable. The spec's for those formats REQUIRE response to 3 Hz from the subwoofer output. So you can rest assured that your receiver will definitely not "clip anything below 20 Hz." It will definitely send sub-20 Hz content to the subwoofer.
Craig

Got a source for that? Id love to read more about it.
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post #11 of 16 Old 10-08-2012, 01:03 PM
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From Dolby's "5.1 Channel Production Guidelines:
Quote:
5.1-channel audio typically consists of five discrete, full range main channels (Left,
Center, Right, Left Surround, and Right Surround) plus an optional band-limited Low
Frequency Effects (LFE) channel for added bass (the .1). Dolby Digital bitstreams
deliver full frequency bandwidth main channels, from 3 Hz to 20 kHz, and a limited
frequency bandwidth LFE channel, from 3 Hz to 120 Hz

Dolby 51 productions guidelines.pdf 487k .pdf file

Or, do a Google search for "Dolby Full Range Channel 3 Hz." You find many references.

Craig
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File Type: pdf Dolby 51 productions guidelines.pdf (487.0 KB, 10 views)

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post #12 of 16 Old 10-08-2012, 03:19 PM
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Quote:
Originally Posted by craig john View Post

From Dolby's "5.1 Channel Production Guidelines:
Dolby 51 productions guidelines.pdf 487k .pdf file
Or, do a Google search for "Dolby Full Range Channel 3 Hz." You find many references.
Craig

According to this webpage at Genelic's website, the LFE channel for both Dolby-HD and DTS-HD is full bandwidth and there is no upper cutoff specification. Now those that want to reproduce the LFE channel as intended need a speaker to go with their subwoofer. biggrin.gif I have the Red Cliff Blu-ray and the DTS-HD LFE channel has content up to about 400 Hz.
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post #13 of 16 Old 10-08-2012, 04:30 PM
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Quote:
Originally Posted by desertdome View Post

Quote:
Originally Posted by craig john View Post

From Dolby's "5.1 Channel Production Guidelines:
Dolby 51 productions guidelines.pdf 487k .pdf file
Or, do a Google search for "Dolby Full Range Channel 3 Hz." You find many references.
Craig

According to this webpage at Genelic's website, the LFE channel for both Dolby-HD and DTS-HD is full bandwidth and there is no upper cutoff specification. Now those that want to reproduce the LFE channel as intended need a speaker to go with their subwoofer. biggrin.gif I have the Red Cliff Blu-ray and the DTS-HD LFE channel has content up to about 400 Hz.




Interesting note about DTS-HD. There is a steep (60 dB per octave) 100 Hz (-3 dB) high pass filter applied in a DTS DECODER.

Table Note (1): in all DTS ‘Coherent Acoustic’ codec the LFE channel is band limited at the encoding stage at 120 Hz. In the DTS-HD codec only [DTS-HD Master Audio™ (lossless) and DTS-HD High Resolution Audio™ (lossy)] the DTS-HD decoder applies a low-pass filter at 100 Hz (-3 dB) with a 60 dB/octave roll-off onto the LFE channel.
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post #14 of 16 Old 10-08-2012, 04:33 PM
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Quote:
Originally Posted by craig john View Post

From Dolby's "5.1 Channel Production Guidelines:
Quote:
5.1-channel audio typically consists of five discrete, full range main channels (Left,
Center, Right, Left Surround, and Right Surround) plus an optional band-limited Low
Frequency Effects (LFE) channel for added bass (the .1). Dolby Digital bitstreams
deliver full frequency bandwidth main channels, from 3 Hz to 20 kHz, and a limited
frequency bandwidth LFE channel, from 3 Hz to 120 Hz

Dolby 51 productions guidelines.pdf 487k .pdf file

Or, do a Google search for "Dolby Full Range Channel 3 Hz." You find many references.

Craig



Even the standard CD / CD player spec reads the same way. There is a 3 Hz capability spec for the low end.
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post #15 of 16 Old 10-08-2012, 04:38 PM
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Quote:
Originally Posted by desertdome View Post

According to this webpage at Genelic's website, the LFE channel for both Dolby-HD and DTS-HD is full bandwidth and there is no upper cutoff specification. Now those that want to reproduce the LFE channel as intended need a speaker to go with their subwoofer. biggrin.gif I have the Red Cliff Blu-ray and the DTS-HD LFE channel has content up to about 400 Hz.
No, you don't want to add a speaker to the LFE channel for the LFE Channel of Dolby TrueHD and DTS-MA. These *are* full range channels, but the LPF of LFE blocks all content above the set point, usually set at 120 Hz. That's exactly what the LPF of LFE id for.

Craig

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post #16 of 16 Old 10-08-2012, 05:05 PM
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Quote:
Originally Posted by J_Palmer_Cass View Post

Interesting note about DTS-HD. There is a steep (60 dB per octave) 100 Hz (-3 dB) high low pass filter applied in a DTS DECODER.
Table Note (1): in all DTS ‘Coherent Acoustic’ codec the LFE channel is band limited at the encoding stage at 120 Hz. In the DTS-HD codec only [DTS-HD Master Audio™ (lossless) and DTS-HD High Resolution Audio™ (lossy)] the DTS-HD decoder applies a low-pass filter at 100 Hz (-3 dB) with a 60 dB/octave roll-off onto the LFE channel.
There I fixed it for you.

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Perfection is not attainable, but if we chase perfection we can catch excellence."

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