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post #1 of 85 Old 11-04-10, 11:52 AM Thread Starter
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Gain Structure for Home Theater Discussion Thread

Please use this thread for any comments or discussion about my article Gain Structure for Home Theater.

Regards,
Wayne
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post #2 of 85 Old 11-04-10, 02:53 PM
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re: Gain Structure for Home Theater: Getting the Most from Pro Audio Equipment in Your System

Hello Wayne,

It's great of you to write this article on such an interesting subject.

You might want to add to this what the impact is of using an AVR with a built-in equalization system such as Audyssey. I've thought about this a little in terms of my Denon, even though I use external amplification only for the powered sub. It strikes me that the effects come from two areas that affect the point at which clipping might occur: the AVR may have different level settings for each speaker, and the static equalization may boost certain frequencies up to 9dB.

In Part 7, where you discuss measuring the maximum voltage from the AVR, the setting of the speaker trim might matter, especially if it was very negative. For purposes of the experiment, it might be best to set it to at least 0dB, or perhaps to its maximum positive value.

In Part 9, where you discuss how much headroom to allow, it would be nice to allow enough headroom for the maximum boost that the equalization system might introduce, e.g., 9dB for Audyssey. This would ensure that no clipping would occur from the voltage peak. The speaker trim might come into play here, too. Obviously if one has verified that clipping does not occur with the trims set to 0dB, and if the AVRs calibration sets a higher trim to achieve reference levels, clipping might now appear. Related to this, adjusting the amplifier's gain to the highest level that avoids clipping at maximum signal affects how the AVRs volume setting is calibrated for reference levels. At this highest possible amplifier gain, you might have a situation where the AVR cannot set the speaker trim low enough to correctly calibrate the volume level.

I don't think a system like Audyssey's DynEQ affects the discussion significantly. As you are recommending doing these procedures with the AVR's volume set to maximum, DynEQ should be providing no boost to the signal. As it might even be providing a reduction in the sub range, if it thinks the levels are above reference, it would probably be best that it be disabled.

I also think any source level adjustment in the AVR does not affect the discussion. Assuming the user calibrates the analog source inputs to give the same volume as the digital inputs, one would hope that these will not drive the levels past the 0dBFS that was used when adjusting the gain.

I think that exhausts my suggestions.

Thanks for writing this,
Bill

Last edited by laser188139; 11-04-10 at 11:26 PM. Reason: fix Audyssey max boost to 9dB from 12dB
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post #3 of 85 Old 11-04-10, 03:36 PM
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re: Gain Structure for Home Theater: Getting the Most from Pro Audio Equipment in Your System

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Wayne A. Pflughaupt wrote: View Post
I apologize for the length of this, but I figure if you’re going to scorch sacred cows you’d better have the documentation to back it up.
I missed the documentation. Where are the distortion, noise floor, and headroom graphs, and information to back this method up?


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Last edited by soho54; 11-04-10 at 03:45 PM.
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post #4 of 85 Old 11-04-10, 05:47 PM Thread Starter
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re: Gain Structure for Home Theater: Getting the Most from Pro Audio Equipment in Your System


Thanks for the thoughtful comments, Bill.


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laser188139 wrote: View Post
You might want to add to this what the impact is of using an AVR with a built-in equalization system such as Audyssey. I've thought about this a little in terms of my Denon, even though I use external amplification only for the powered sub. It strikes me that the effects come from two areas that affect the point at which clipping might occur: the AVR may have different level settings for each speaker, and the static equalization may boost certain frequencies up to 12dB.
Quote:
In Part 9, where you discuss how much headroom to allow, it would be nice to allow enough headroom for the maximum boost that the equalization system might introduce, e.g., 12dB for Audyssey. This would ensure that no clipping would occur from the voltage peak. The speaker trim might come into play here, too. Obviously if one has verified that clipping does not occur with the trims set to 0dB, and if the AVRs calibration sets a higher trim to achieve reference levels, clipping might now appear.
Yeah, good point about Audyssey. Didn’t even consider it, because I don’t use it. But I don’t really see any issues with it WRT my home-grown gain-setting process. Maximum clean pre amp output is the maximum usable output, whether or not Audyssey’s EQ is there or not. I assume that the AVR manufacturers that incorporate Audyssey into their receivers have taken care of all that. I did note that if people were concerned about pre amp headroom when setting the amp gains, they can use a lower AVR volume setting than max. Seems to me that should be sufficient.

EDIT: Part 9 has been re-worked to cover Audyssey and other auto-EQ features, as well as outboard equalization.


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In Part 7, where you discuss measuring the maximum voltage from the AVR, the setting of the speaker trim might matter, especially if it was very negative. For purposes of the experiment, it might be best to set it to at least 0dB, or perhaps to its maximum positive value.
Right. And I did recommend setting speaker levels to their highest setting in the 3rd paragraph under the “How to determine your AVR’s output voltage: “My AVR has all speaker-level settings referenced to the main left and right channels, which are fixed and cannot be adjusted in the menu. If your AVR allows for adjustments for the front left and right channels, they should be set to maximum for this exercise, as should the center channel and subwoofer if you intend to measure those too.”


Quote:
Related to this, adjusting the amplifier's gain to the highest level that avoids clipping at maximum signal affects how the AVRs volume setting is calibrated for reference levels. At this highest possible amplifier gain, you might have a situation where the AVR cannot set the speaker trim low enough to correctly calibrate the volume level.
I expect this would only be an issue if someone was mixing high- and low-efficiency speakers in their system. It would be the efficient speakers that would be dialed back in the AVR. But since efficient speakers don’t need much power, it might not matter. If it did – dialing the AVR speaker levels back would mean the amp gains could be ratcheted up to compensate. Alternately, the speaker adjustments could just be performed via the amp gains instead of the AVR menu.


Regards,
Wayne



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post #5 of 85 Old 11-04-10, 06:41 PM Thread Starter
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re: Gain Structure for Home Theater: Getting the Most from Pro Audio Equipment in Your System


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I missed the documentation. Where are the distortion, noise floor, and headroom graphs, and information to back this method up?
Relevant graphs were presented in Parts Three and Five. Perhaps not everything you're looking for was included, but it's far more graphs and documentation than you'll find in the typical PA system gain structure article.

I don’t have a problem answering some of the question you edited out of your post. I don’t think this topic as it relates to home theater has ever examined in depth before, so it’s natural that people will have questions and concerns. I tried to be thorough, but I doubt I thought of everything.


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It is also possible/common to get higher than what should be 0dBFS out of, well pretty much everything.
Well, it’s the maximum a DVD disc itself will put out, as it’s a digital media and will not support a higher level without distortion. I assume the DVD manufacturers are aware of that and will make sure the audio on their discs does not go beyond 0 dBFS and distort. 0dBFS is also the maximum a DVD player will output, since a digital output it’s passing the signal straight along to the AVR. I assume the same can be said about things like cable TV and sat receivers as well.

It is a bit different with an AVR, of course, since the pre-amp outputs are Vrms. But it would require source component connected to the AVR with a hotter signal than 0 dBFS to get more output from it than would be provided with a DVD player or similar media component. I can’t imagine what that would be, unless someone’s plugging their Behringer XENYX mixer to their AVR. If you want to count something like that, then you’re correct: It’s possible to get higher than a 0 dBFS signal. But by and large setting amp gains with the signal generated by the 0 dBFS signal source is perfectly sufficient.


Quote:
There are a couple of other explanations that seem a bit off as well, form a pro audio mindset.
And that’s perfectly fine. This is not pro audio. This is home theater. The problem people have been having is thinking the “pro audio mindset” somehow became relevant to them when they added a piece of professional equipment to their home theater system. As thoroughly discussed in Part 2, a pro audio-styled gain structure protocol does not necessarily cross-reference to home audio.


Quote:
This "Make sure all speaker-level settings in the AVR's menu are set to max," is just bad advice. It is the flaw behind the whole thing. An AVR like any other device has a set operational range, and headroom built in.
The “set speakers to max” thing is only for the purposes of setting the amp gains. After that you’re supposed to adjust the relative speaker levels as it’s normally accomplished, with the AVR’s rotating pink noise sound, a calibration disc, etc. Headroom is restored when you turn everything back down and use the system as normal. You weren’t running your system wide open before gain-structuring, and you won’t be afterwards.

But it’s imperative to have the maximum signal on tap when setting the amp gains. Otherwise you will end up with the gains being set higher than they need to be, which can lead to more noise from the amp than you’d get with lower gain settings.

Besides, my “maximum clean level” procedure for setting amp gains is virtually identical to what Rane outlines in their gain structure article, which I linked in Part 2. Have you read it?

Regards,
Wayne



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post #6 of 85 Old 11-04-10, 09:52 PM
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re: Gain Structure for Home Theater: Getting the Most from Pro Audio Equipment in Your System

So the gyst of it is...
I need to find not only a HPF and DSP for my sub, but has to be a low noise HPF and DSP?
Great.
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post #7 of 85 Old 11-05-10, 11:17 AM Thread Starter
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re: Gain Structure for Home Theater: Getting the Most from Pro Audio Equipment in Your System


Not really, noise from substandard components is virtually no issue with sub woofers because it is not audible. This is why you’ll hardly ever see noise specs of any kind for manufactured subs. Sorry for not clarifying that, I’ll make the necessary changes to the text.

By the way, unless you are bottoming out your sub, or driving the amp to clipping, you don't need a high pass filter.

Regards,
Wayne



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post #8 of 85 Old 11-05-10, 11:59 AM
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re: Gain Structure for Home Theater: Getting the Most from Pro Audio Equipment in Your System

Fine and outstanding article...
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post #9 of 85 Old 11-05-10, 06:42 PM
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re: Gain Structure for Home Theater: Getting the Most from Pro Audio Equipment in Your System

I edited them out because I felt the questions would turn things into a line by line discussion, and I have no desire to do that. I have been down this road many times, and this does not seem like the proper place. That was me, stepping out quietly.

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Relevant graphs were presented in Part Three. The “sacred cow” I was referring to was the popular maxed-out signals canard. I’ll go back and change the text to make better sure the point is made.
I still do not follow then. You say that which is true as structures gain has nothing to do with maxed-out signals, and later add "
Quote:
Gain structure is merely an exercise to insure that the pro amps are getting enough signal to drive them to maximum output.
" this is not so accurate. The idea is to pass the cleanest signal possible along the signal chain. Live sound extends this to the amps, but that is to protect fidelity, and equipment as well. It is not for the sake of getting maximum output.


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OdBFS is also the maximum a DVD player will output, since a digital output it’s passing the signal straight along to the AVR. I assume the same can be said about things like cable TV and sat receivers as well.
0dBFS on a disk has a fickle relationship with what you end up with out of the AVR analogue outputs. +0dBFS signals are very common, and are produced by the DAC conversion, bass management, and the master volume control alone, and as a group. There are also oddities with some devices and 0dBFS signals as well where 0dBFS may not be as loud as signals just a few dB lower in intensity. Most every commercial CD released in the last half a dozen years can produce +0dBFS. It's even worse with most mp3s. No one is ripping DVDs in raw format, but I see no reason for it not to be the similar.


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Wayne A. Pflughaupt wrote: View Post
And that’s perfectly fine. This is not pro audio. This is home theater. The problem people have been having is thinking the “pro audio mindset” somehow became relevant to them when they added a piece of professional equipment to their home theater system. As thoroughly discussed in Part 2, a pro audio-styled gain structure protocol does not necessarily cross-reference to home audio.
If you put a piece of differently referenced gear into your signal chain, it is now relevant. Structure, protocol, terms, have nothing to do with it. It is basic electronics. Home gear runs on the exact same base principles pro gear does. Once you add a device that does not conform to the same default "home" reference, it pays to think about the things home audio takes for granted as a given.


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Wayne A. Pflughaupt wrote: View Post
The “set speakers to max” thing is only for the purposes of setting the amp gains. After that you’re supposed to adjust the relative speaker levels as it’s normally accomplished, with the AVR’s rotating pink noise sound, a calibration disc, etc. Headroom is restored when you turn everything back down and use the system as normal. You weren’t running your system wide open before gain-structuring, and you won’t be afterwards.

But it’s imperative to have the maximum signal on tap when setting the amp gains. Otherwise you will end up with the gains being set higher than they need to be, which can lead to more noise from the amp than you’d get with lower gain settings.

Besides, my “max level” procedure for setting amp gains is virtually identical to what Rane outlines in their gain structure article, which I linked in Part 2. Have you read it?
Starting at the end... If you look at part 4 in the Setting Power Amplifiers section, you see that you need to identify the max clean signal from everything up until that point first. SOP. Just turning up the levels to max isn't the way to go. Most AVR outputs will be distorting and clipping before the max anyway, so it's kind of arbitrary. You will clip the amp before the input sensitivity voltage is reached. You are tying to get around clipping the amp by raising the AVR to levels it should never normally encounter, but doesn't this still leave the amp "with the gains being set higher than they need to be?" This leaves the amount of gain the AVR can add to a channel out of the mix. With 12dB you should be alright, but what about models with only 6dB?

What happens when the same AVR and amp are used in two setups with one having low sensitivity speakers, and the other high? What happens when you switch out an amp of higher/lower power? Now add a Pro EQ, and run though again? Which one was the optimal setup?

It seems like setting up from the end of the signal chain to the front.


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post #10 of 85 Old 11-05-10, 09:18 PM Thread Starter
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re: Gain Structure for Home Theater: Getting the Most from Pro Audio Equipment in Your System


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I still do not follow then. You say that which is true as structures gain has nothing to do with maxed-out signals, and later add "
Quote:
Gain structure is merely an exercise to insure that the pro amps are getting enough signal to drive them to maximum output.
The discussion on the home audio forums, as least what I’ve seen in the past ten years, has been that pro gear requires a +4 dBU signal, and if you can’t get that from your home theater pre amp/AVR you’re going to have noise, reduced dynamic range, etc. In most cases it’s possible to drive a pro amp with a consumer front end, especially if one is chosen with an ample sensitivity rating.


Quote:
0dBFS on a disk has a fickle relationship with what you end up with out of the AVR analogue outputs. +0dBFS signals are very common, and are produced by the DAC conversion, bass management, and the master volume control alone, and as a group. There are also oddities with some devices and 0dBFS signals as well where 0dBFS may not be as loud as signals just a few dB lower in intensity. Most every commercial CD released in the last half a dozen years can produce 0dBFS.
You’re “mixing and matching” the digital dBFS scale with the analog Vrms scale. 0 dBFS is the highest possible digital signal; there is no such thing as “+0dBFS.” If a component somehow adds some boost to the signal in the analog domain (i.e. after the digital-to-analog conversion), that’s of no relevance. The measurable-voltage signal at the AVR’s main pre outputs will reflect that, and any voltage measurement will still be valid.


Quote:
If you put a piece of differently referenced gear into your signal chain, it is now relevant. Structure, protocol, terms, have nothing to do with it. It is basic electronics. Home gear runs on the exact same base principles pro gear does. Once you add a device that does not conform to the same default "home" reference, it pays to think about the things home audio takes for granted as a given.
There is a long and established history on the home audio forums that trying to apply a pro-audio-styled gain structure protocol has caused a lot of confusion, if not out-and-out problems, such as we see here in this post from another Forum:
Quote:
I was considering a DCX2496 but had worries about three things. First, the pro level; second, how to get a full signal to the DCX for good digitization (i.e. keep the volume control after the digitization to avoid digitizing a signal 50 dB below max) ...
As another example I recall at least one thread at AVS I came across while researching this, of a guy who had added a Behringer DCX2496 to his system. Following the pro audio protocol, he’d managed to get his levels hot enough to get a good reading on the DCX input meters (forget how he accomplished that). The result: An added 6 dB of noise (by his account), and problems clipping the inputs of his home audio amplifiers. Then there was the case I linked at the end of the article.

Sure, it “it pays to think about the things home audio takes for granted as a given.” For instance, a couple of the things home audio has always taken for granted is quiet noise floors and not having to jack around with amp gains. IMO the main thing to be aware of is system compatibility – i.e. making sure the home and pro gear chosen is compatible. Such as not trying to use an amp with a higher sensitivity voltage than your AVR can generate. Or the possibility that cheap pro gear may add a lot of background noise. Hopefully with this piece people will now be able to determine where the weak link is in their signal chain, if there is one.


Quote:
Starting at the end... If you look at part 4 in the Setting Power Amplifiers section, you see that you need to identify the max clean signal from everything up until that point first. SOP. Just turning up the levels to max isn't the way to go. Most AVR outputs will be distorting and clipping before the max anyway, so it's kind of arbitrary. You will clip the amp before the input sensitivity voltage is reached. You are tying to get around clipping the amp by raising the AVR to levels it should never normally encounter, but doesn't this still leave the amp "with the gains being set higher than they need to be?" This leaves the amount of gain the AVR can add to a channel out of the mix. With 12dB you should be alright, but what about models with only 6dB?
I expect people have the good sense to know if they are getting distortion and can easily tweak things to get the desired results. As I’ve noted more than once, anyone worried about the pre-outs clipping can easily use a lower setting for gain structuring.


Quote:
What happens when the same AVR and amp are used in two setups with one having low sensitivity speakers, and the other high? What happens when you switch out an amp of higher/lower power? Now add a Pro EQ, and run though again? Which one was the optimal setup?
I would hope that people would have the good sense to re-calibrate if they make equipment changes. Not sure why you expect that they wouldn't.

It’s impossible for me to conceive of or address every scenario in existence. However, following my suggestions HT enthusiasts hopefully have the tools to determine for themselves what their system needs.

EDIT: In light of your concerns about not addressing systems with low sensativity speakers etc., and Bill's comments along the same lines in his post, I've added new text to Part 9 to clarify that my suggestions are general in nature and cannot possibly address every system configuration in existance. I’ve also added text to cover gain structure with both outboard equalizers and auto-EQ systems like Audyssey. Thanks for bringing these things to my attention.

Regards,
Wayne



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