Gain Structure for Home Theater Discussion Thread

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Wayne A. Pflughaupt

Discussion Starter · Nov 4, 2010

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

Regards,
Wayne

21 - 40 of 86 Posts

dsime42

· #21 · Nov 9, 2011

Re: Gain Structure for Home Theater: Getting the Most from Pro Audio Equipment in Your System

Wayne A. Pflughaupt said:
That would be contrary to standard gain structure protocol. According to most professional references, post-pre amp signal boosting is not recommended because it will increase the noise floor from the source component and pre amp. This is supported by the Rane article referred to in Part 2 (among other sources), which notes that the only gain changes that should be effected in downstream processors is to counter what might come from the processor itself – like an overall change in signal strength from an equalizer, for instance. The signal is not – and indeed should not – be “amplified” from one component to the next. I think you’d be hard pressed to come up with any professional references that say otherwise.

...

Quiet (read quality) equipment is what determines system noise, not signal levels. Every gain structure-related thread I’ve ever seen that dealt with a noise issue, the problem was ultimately isolated to a certain piece of equipment (a classic example can be seen in the link to an AVS thread found in Part 4). I’ve yet to see a thread where a noise issue was determined to be caused by inappropriate signal levels.

Hi
I'm just a little confused here.
The "post-pre amp signal boosting is not recommended" statement seems diametrically opposed to your Figure 2 where 3dB is added between the Notch Filter and again before the Limiter, but I don't see anything on that graphic labeled "preamp" hence my confusion.

Also
When I look at Figure 1 I see a System Dynamic Range (SDR) of 72dB and the Figure 2, after alignment, shows an SDR of 90 dB. Then in the rest of the article you make the case that the original 72dB was enough and in fact loss of an additional 6 or 12 dB would not be an issue. Sorry I think I missed something.

Wayne A. Pflughaupt

Discussion Starter · #22 · Nov 10, 2011

Re: Gain Structure for Home Theater: Getting the Most from Pro Audio Equipment in Your System

soho54 said:
What I posted is fact, and can be easily demonstrated. The input and output levels at every stop along the chain will effect the total/final/in room system noise floor.

This problem could easily be avoided by making sure the input and output levels are the same for each processor in the signal chain – as they should be. Standard pro-audio gain structure protocol, that in this case works for home theater too.

soho54 said:
I have a mixed pro/home setup that is dead silent with my main set of speakers, but I demo a lot of gear, and know that it is not dead silent with other speakers hooked up. It takes different amps, processors, and a completely different gain setup to get close to dead silent with say the DSL SH60s in my room.

If your system is dead silent and you get noise after changing out a piece of equipment, it should be obvious that it is an inferior piece of gear.

soho54 said:
I going to give up now.

We are still waiting for your recommendation for a better method for “regular Joes” who don't have any professional calibration equipment.

dsime42 said:
I'm just a little confused here.
The "post-pre amp signal boosting is not recommended" statement seems diametrically opposed to your Figure 2 where 3dB is added between the Notch Filter and again before the Limiter...

Yes, they do seem contradictory. The graph came from a different reference source than the Rane article. As I noted in Part 1 a few paragraphs above the graphs, it’s not uncommon for different gain structure references to have a certain amount of inconsistencies from one to the next. For a mixed home/pro system, the Rane information is what's relevant, because we don’t use outboard components like notch filters and limiters that have their own gain-boosting capabilities (the exception being sophisticated systems that use electronic crossovers or digital speaker processors).

...but I don't see anything on that graphic labeled "preamp" hence my confusion.

Keep in mind that the graphs depict a professional PA system. In a PA system, the mixing console has essentially the same function as a home audio pre amp – i.e. it’s the piece that all the input sources plug into.

When I look at Figure 1 I see a System Dynamic Range (SDR) of 72dB and the Figure 2, after alignment, shows an SDR of 90 dB. Then in the rest of the article you make the case that the original 72dB was enough and in fact loss of an additional 6 or 12 dB would not be an issue. Sorry I think I missed something.

Sorry but I have no idea how you arrived at the conclusion that I said the original 72 dB SDR was adequate. The primary purpose for those two graphs was to show that a proper gain structure would improve system dynamic range. The equipment depicted in the graphs is pro gear from top to bottom, and as such isn’t specifically relevant to a mixed home/pro system. The only reference I made to a “loss” of signal not mattering was specifically referring to any 24-bit digital processors used in a home system downstream from the pre amp.

Regards,
Wayne

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jianhua1975

· #23 · Nov 10, 2011

Re: Gain Structure for Home Theater: Getting the Most from Pro Audio Equipment in Your System

Hi, Wayne:
just some junior questions:
i am using pure Pre amp(7.1) + poweramp(5 channel) + powered Sub.
and i'd like to know what you are refering to for "Gain control", " volume control" and "speaker level setting" in pure preamp? i only know that Volume control shall be the volume Knob in Preamp's front panel.
what about other two, shall be in the menu right??

and for Preamp setting as analog input with Bypass(is that what you mentioned as setting to "bypass" , "Stereo","direct"? ), which means there is no Dsp working for bass management at all. so Subout will be no signal, and Xover point setting will be bypassed also, in this case how to measure sub?

Wayne A. Pflughaupt

Discussion Starter · #24 · Nov 10, 2011

Re: Gain Structure for Home Theater: Getting the Most from Pro Audio Equipment in Your System

i am using pure Pre amp(7.1) + poweramp(5 channel) + powered Sub.
and i'd like to know what you are refering to for "Gain control", " volume control" and "speaker level setting" in pure preamp? i only know that Volume control shall be the volume Knob in Preamp's front panel.

what about other two, shall be in the menu right??

Yes, with an AV pre-amp, speaker-level settings are typically in the menu. Gain controls for the various input sources are kind of rare, but they would be in the menu, too.

and for Preamp setting as analog input with Bypass(is that what you mentioned as setting to "bypass" , "Stereo","direct"? ), which means there is no Dsp working for bass management at all. so Subout will be no signal, and Xover point setting will be bypassed also, in this case how to measure sub?

Many AV receivers (or pre amps) keep the subwoofer output active when you set it for “Bypass” or “Stereo Direct.” If yours isn’t like that, just go ahead and use whatever setting is needed to activate the subwoofer output, so you can take your voltage measurements. :T

Regards,
Wayne

rob92266

· #25 · Mar 31, 2012 (Edited)

Re: Gain Structure for Home Theater: Getting the Most from Pro Audio Equipment in Your System

i just cant figure it out, so this is what i am running for gear first of all:

marantz sr7000 avr
2 - dual 15" jbl bins with jbl horns for the fronts
1 - center channel speaker
1 - 15" peavy sub
2 - b & w speakers for the surrounds
1 - behringer mx882 line level matching/splitter/mixer
1 - behringer epq1200 for the surrounds
1 - behringer epq1200 for the center and for the sub
1 - behringer epq2000 for the fronts

total power is 4400 watt

this is how i have it hooked up, i hope this is right.

from the avr preouts, fronts, center, sub and surrounds connect to the inputs on individual channels ( 1 through 6 )on the mx882 with rca to xlr, then from the mx882 outputs for each channel (using xlr cables )go to the dedicated amps, and the speakers are connected from the amps, it just seems to me that since i am running 4400 watts that it should be much louder, the amps are maxed out and the volume control on the avr has a range from -60 to +15, so when i am watching tv the volume is set at around -24, so i dont know if this is correct or someone can help me out here, and help would be appreciated

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Wayne A. Pflughaupt

Discussion Starter · #26 · Mar 31, 2012

Re: Gain Structure for Home Theater: Getting the Most from Pro Audio Equipment in Your System

See this cross-posted thread.

Regards,
Wayne

sportflyer

· #27 · May 11, 2012

Re: Gain Structure for Home Theater: Getting the Most from Pro Audio Equipment in Your System

Wayne,

I am thinking of using a Pro Crossover for example a DBX 223( or similar unit from Behringer, ART etc) as a crossover for bass management between a tube preamp and SS power amp. to integrate a SVS subwoofer Now that I read your articles above I am wondering whether this is a suitable application of the DBX 223 as a bass management unit in a home Stereo environment. BTW I am already using a BFD for Sub EQ

I have questions re the gain settings of this unit. Does 0db in the gain dials mean unity gain ?

Maybe its better to find a used XO unit designed specifically for home audio like the Paradigm X-30 , Energy EAC etc. ? Bryston XO unit is too costly for me.

Advice?

Wayne A. Pflughaupt

Discussion Starter · #28 · May 12, 2012

Re: Gain Structure for Home Theater: Getting the Most from Pro Audio Equipment in Your System

Yes, a 0 dB setting on the input and output knobs is unity gain.

There’s no reason a pro crossover won’t work, from a functional standpoint. However, with any budget pro audio gear there is a concern that it might not be as quiet or as clean as good home equipment. I’d suggest subjecting it to the battery of tests I outlined in Part 8 to make that determination.

Naturally, this is only a concern if you intend to use both the high and low pass outputs from the crossover. If you’re only using the low pass (for the subs), then noise is not an issue.

Regards,
Wayne

sportflyer

· #29 · May 12, 2012

Re: Gain Structure for Home Theater: Getting the Most from Pro Audio Equipment in Your System

Wayne A. Pflughaupt said:
Yes, a 0 dB setting on the input and output knobs is unity gain.

There’s no reason a pro crossover won’t work, from a functional standpoint. However, with any budget pro audio gear there is a concern that it might not be as quiet or as clean as good home equipment. I’d suggest subjecting it to the battery of tests I outlined in Part 8 to make that determination.

Naturally, this is only a concern if you intend to use both the high and low pass outputs from the crossover. If you’re only using the low pass (for the subs), then noise is not an issue.

Regards,
Wayne

I was planning to use it for LP and HP. So I think I might be better off buying a used XO specifically designed for home stereo. Used equip from Paradigm, Mirage, Energy and Outlaw are about the same price as new Pro XO from Behringer, DBXpro , Rane etc . This way I dont have to worry about noise floor and dynamic range . Looks like I will be patiently scouring the ads

Tks

apilon

· #30 · Mar 10, 2013

Re: Gain Structure for Home Theater: Getting the Most from Pro Audio Equipment in Your System

Wayne

very informative articles. My question is i drive a DIY sub with a Behringer EP-4000 which is connected to an Onkyo TX-NR818

Everyone is telling me to set the ep4000 gain to max and use the sub trim to bring it down to 75 DB but even with the trim max out at -15 db the spl is registering over 80 db

How can i use your article to properly do a gain structure on my sub??

Alain

Wayne A. Pflughaupt

Discussion Starter · #31 · Mar 11, 2013

Re: Gain Structure for Home Theater: Getting the Most from Pro Audio Equipment in Your System

Hey Alain,

Typically the amp would only need to have its gains run wide open if it was getting a weak input signal. However, from what I’ve picked up on various forums, Onkyo receivers have unusually high voltage levels from their RCA outputs. So starting with the amp’s gains maxed out is a bad idea in your case. Your best bet would be to ignore what “everyone” is telling you and follow the simple steps laid out in Part 9 of the article. :T

Regards,
Wayne

apilon

· #32 · Mar 11, 2013

Re: Gain Structure for Home Theater: Getting the Most from Pro Audio Equipment in Your System

Wayne A. Pflughaupt said:
Hey Alain,

Typically the amp would only need to have its gains run wide open if it was getting a weak input signal. However, from what I’ve picked up on various forums, Onkyo receivers have unusually high voltage levels from their RCA outputs. So starting with the amp’s gains maxed out is a bad idea in your case. Your best bet would be to ignore what “everyone” is telling you and follow the simple steps laid out in Part 9 of the article. :T

Regards,
Wayne

Thanks Wayne

I believe i will need to perform step 7 before to get the sub maximum usable clean output ?? If so do i need to measure the mains also as stated or can i just measure the sub output?

Finally just to make sure i understand correctly, step 3 adjust the level of all channels utilizing outboard amplifiers to their max settings . Are you refering to the AVR trim level that i should max out to +15DB ??

Wayne A. Pflughaupt

Discussion Starter · #33 · Mar 11, 2013

Re: Gain Structure for Home Theater: Getting the Most from Pro Audio Equipment in Your System

Part 7 is mainly to help people determine if their receiver generates enough clean voltage to drive a pro amp. We already know that yours can, so you can skip that part. Just set your AVR’s sub output for 0 dB and adjusted the amp’s gains as needed, per Part 9.

Regards,
Wayne

dsime42

· #34 · Mar 11, 2013

Re: Gain Structure for Home Theater: Getting the Most from Pro Audio Equipment in Your System

Hi Wayne
I look forward to reading the rest of this article but I started on #5 (Myths) and am having a problem with a couple of your statements.

RE: "A 24-bit system in particular can shed several hundred thousand LSBs from its 16,777,216 quantization steps"
While it may be true that a 24-bit system could "shed several hundred thousand STEPs from its 16,777,216 quantization steps" it cannot shed more BITs than it has. Hence a 24 bit system will have One (1) MSB and 23 bits that are less significant and could possibly be called LSBs though once you get past halfway (12 bits) it starts to become semantics.

Any way you slice it you can not shed more bits than exist. ie 24

RE: The chart you show with the three bit system.
You have a left axis labelled "000 001 010 011 100 101 110 111" and you illustrate the loss of a BIT as being synonymous with the loss of the "000" state. This is incorrect
Loss of a bit isn't "really loss of the bit it is loss of the "usefulness" of the bit and the LSB is also NOT the lowest state representable by the system as you have shown.
A more correct chart would have had its left axis labelled "00x 00x 01x 01x 10x 10x 11x 11x". Note that ALL of the LSBs on the axis have been changed to 'x' representing the fact that while they still exist they cannot be relied on to provide [good] data.

In addition the sharp red line showing the steps should be changed to reflect this "uncertainty" by becoming a pinkish-grey area encompassing that part of the graph where the LSB could be either a '1' or a '0' .

Following the top edge of this grey area would show that now you actually have a TWO (2) bit system with another bit worth of grey area below it. The "uncertain area", where "valid data" does not exist is commonly referred to as noise.

An interesting extension of this chart would be to "lose" two (2) LSBs.
With the chart as you depict it only "two states" would be lost but with the axis label correctly it would depict a one (1) bit system with a considerable pink-grey area.

Of course the logical conclusion to this would be a 3-bit system with the loss of ... ... wait for it

... the three (3) LSBs the label would be an uninteresting list of 'xxx' and the entire chart would be pink-grey and it would be easy to see that the chart is nothing but noise.

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apilon

· #35 · Mar 11, 2013

Re: Gain Structure for Home Theater: Getting the Most from Pro Audio Equipment in Your System

Wayne A. Pflughaupt said:
Part 7 is mainly to help people determine if their receiver generates enough clean voltage to drive a pro amp. We already know that yours can, so you can skip that part. Just set your AVR’s sub output for 0 dB and adjusted the amp’s gains as needed, per Part 9.

Regards,
Wayne

Got it Thanks

2 more questions and i am on my way......

1. Do i leave the clip limiter on or off for that test on the ep4000?

2. as for the avr volume to i set it to max or 0db reference level?

Wayne A. Pflughaupt

Discussion Starter · #36 · Mar 12, 2013

Re: Gain Structure for Home Theater: Getting the Most from Pro Audio Equipment in Your System

dsime42 said:
Hi Wayne
I look forward to reading the rest of this article but I started on #5 (Myths) and am having a problem with a couple of your statements.

Thanks for clarifying, desime. :T The 3-bit graph came from Wikipedia (http://en.wikipedia.org/wiki/A/D_converter). Not being well versed in the finer points of A/D conversion, when they showed a quantization step as a LSB(it) I presumed that “bit” and “step” were the same thing.

The point of the discussion was to show that despite the fables that have circulated the home audio forums for nearly 15 years, 24-bit processors are essentially immune to poor input signal levels – you didn’t shoot that part down, so hopefully I’m okay there!

Regards,
Wayne

Wayne A. Pflughaupt

Discussion Starter · #37 · Mar 12, 2013

Re: Gain Structure for Home Theater: Getting the Most from Pro Audio Equipment in Your System

apilon said:
2 more questions and i am on my way......

1. Do i leave the clip limiter on or off for that test on the ep4000?

I’d leave it off for the gain setting process. The whole purpose of the gain structure exercise is to make sure the amp clips at the same time as the pre-amp. So, once that’s done, the limiters merely add an extra layer of protection.

That said, I think most people would agree that 30 Hz is way too high a high pass filter for a home theater subwoofer. That essentially reduces the extension of a beefy DIY sub to par with the typical 10-inch manufactured sub.

2. as for the avr volume to i set it to max or 0db reference level?

With your receiver, which has perhaps 2-3 times the output of most others, I don’t think you have to be overly concerned by all this. You can just adjust the amp’s gains for subwoofer level setting the same way that you would for a common powered sub.

Regards,
Wayne

apilon

· #38 · Mar 14, 2013

Re: Gain Structure for Home Theater: Getting the Most from Pro Audio Equipment in Your System

Good evening Wayne

I performed the steps in part 7 sub trim 0db played the sin wave but bottom line i had to max out the Onkyo volume to +18db in order to get the Behringer ep4000 to clip and got a steady clip light at +25db on the ep

Thanks for your help

Alain

tomstrade

· #39 · Mar 20, 2014

Re: Gain Structure for Home Theater: Getting the Most from Pro Audio Equipment in Your System

Wayne, thanks for this great thread on gain setting. I guess I'm a little late to the party.

I have a Denon 4520 that I'm trying to match up with a Crown XLS2500. Running through your steps I am a bit stuck determining the 4520 preout harmonic distortion threshold. I downloaded your test tones to a USB stick and are running the tones off the USB stick and 4520's MP3 decoder. Using the 1kHz sine signal I can easily detect harmonic distortion once I hit 78 on the Denon volume control (whereby the range is set for 0-98). The problem I have is that I hear this distortion at 78 no matter how high or low the speaker levels are set for - on the 4520, that would be -12 to +12dB. Is this typical? Wouldn't I expect to at least "move" the harmonic distortion point along the volume continuum as I change the speaker levels? Any reason why I can only hear it at volume level 78?

Wayne A. Pflughaupt

Discussion Starter · #40 · Mar 30, 2014

Re: Gain Structure for Home Theater: Getting the Most from Pro Audio Equipment in Your System

Hey Tom,

So you’re saying that you run the Denon’s master volume up to 78, and at that point you can hear the distortion begin. And from there if you adjust the per-channel level from the menu for the speaker you’re hearing, that there is no change? IOW, you can reduce the volume of the speaker that way and still hear distortion?

If that’s the case, yes I would think that’s unusual, but then again there are just too many receivers on the market for me to know if this is typical or not, and digital processing can be tricky.

Regards,
Wayne

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