Poll: How do YOU set your gain structure???? - Page 2

What can cause confusion is that "db" is used in numerous domains: electrical and acoustic.

Addition:
"The decibel ( dB) is used to measure sound level, but it is also widely used in electronics, signals and communication. The dB is a logarithmic unit used to describe a ratio. The ratio may be power, sound pressure, voltage or intensity or several other things."

From:
http://www.animations.physics.unsw.edu.au/jw/dB.htm
Edited by WVSyd - 2/19/13 at 7:42am

I believe that recommendation was for someone having trouble with too much pre-out voltage on the sub pre-out. My recommendation was to raise the trims on the mains and therefore lower the main listening volume to keep the sub pre-out voltage below the clipping threshold. IIRC Audyssey was setting the sub trim to -12 and they were still clipping the next device after AVR at listening volume.

Yes, the other channels will still be governed by their own subset of conditions including their own gain structure if using an external amplifier and can be overdriven. Also if doing this, "Reference" is no longer "Reference" its offset downward roughtly by the amount you raise the trim on the mains. I don't buy into "Reference" BTW its different for each system and normally constrained by distortion IMHO. Folks who listen to their stuff at "0" "Reference" on conventional towers or bookshelf speakers on AVR power must hear things different than I do.

so what's the proper one in the context of output voltage and its effect on the dynamic range? is it correct to say that if output voltage is limited to 1/2 of the max clean output then the dynamic range is shrunk by 6 dB SPL?

Perhaps I misunderstand your question ( you had the relationship established prior in post 30 )
What would be reduced is the output level.

http://www.allaboutcircuits.com/vol_3/chpt_1/5.html
http://www.sengpielaudio.com/calculator-amplification.htm

For example: Some amplifier makers will state db gain at specified input voltages ( Crown for instance )

http://www.crownaudio.com/db-volts.htm

An example of setting using Crown amps:
http://www.crownaudio.com/media/pdf/apps/The%20Missing%20dB.pdf

http://www.communitypro.com/files/literature/tech%20notes/DB_CALC_TECH.pdf
Edited by WVSyd - 2/19/13 at 8:04am

You remember correctly, that was the original problem you addressed. This scenario is different however - AVR sub output level after Audyssey is short of the max clean output used for the gain structure, the amp cannot be driven to its max capacity with this input signal. Is it a problem or I am over thinking it?

^ This would leave dynamic range and output on the table.

EDIT: Assuming your power limited

yeah, but depending on how much lower the output is, its easy to run out.
say I set gain structure with 8V output signal but Audyssey tapped it at 4V. This should limit the max output by 6dB (t.y. WVSyd ) or 1/4 of the max power capacity of the amp. IOW, even though I may have a 1kW amp I'd only use 250W with these settings.
Is this correct or I made a total fool of myself yet another time?

Excuse this question: How is your Audyssey implemented?
( I've read the installers guide for external units like an SC-1 Audyssey MultEQ XT )

mine is integrated XT32 / Denon AVR4311ci. I am not sure if this answers your question.

I was confused by The voltage numbers didn't make sense in the context I am familiar with.
* I'm not familiar w your Denon and I'm not an Audyssey expert
( I understand setting gain in other contexts however )

the numbers are for illustrative purposes only.
Why did you find them unusual though? Is it unrealistic to find clean sub output around 8Vrms? I know that Denons can do 4Vrms at < 0.1%THD + N on speaker channel preamp outputs. Subwoofer output would definitely provide higher voltage. I remember reading that sub output on Onkyo AVRs measured close to 9Vrms.

Anyway the point is that there is no guarantee that Audyssey will set sub output at or even close to that (max clean output) level.
AFAIK, the actual levels set by Audyssey would depend on sensitivity of the individual speakers and SPL at the measuring position.
The individual channel trims are set in such a way that (1) all speakers play at the same level and (2) make the system play at reference level when the master volume is set to 0 dB. The " Audyssey tapped it at 4V" part in my example corresponds to the calibrated sub output voltage with the master volume is set to 0 dB.

I sort of do my gain structure the way Bassthathz does it using the WOTW pod scene and a couple of other high output sub tracks to first set my input gain on the DCX then output gain to make sure I am not clipping those signals but I do so at first with all the speakers and subs off. I then only turn on my sub amps and adjust there output just below clipping and all this is done at the highest level I will play my system. I also have a SMS-1 in the mix before the DCX and it is set at unity gain of 16.

I always wonder if I am doing it right though but this is the only way that makes sense to me, clipped signals are bad so I figure this is the best way to avoid them.

The only thing bad about this is; you never know if a BR down the road will have much hotter bass that will clip your amp. The hottest signal your AVR will see from you player will be a 0db signal. If you are safe with this signal, you never have to worry about a movie clipping anything down the road, regardless of how hot it is recorded (as long as you don't exceed the volume level tested at).

The external SC-1 device I referenced has a max input voltage rating of 2.5V.

Consumer line level output voltage standard is lower.
Most consumer devices can easily exceed this voltage - as can your Denon at it's preamp output jacks.
An amplifier is often built with the expectation of input voltage of 0.775 volts or 1.4 volts or 2.34 volts ( from Crown amp specs ).
Some amps may have their input stages overloaded with higher input voltage.
( I have had to reduce output voltage of some source components that exceeded a power amplifier's input sensitivity ratings. )
Edited by WVSyd - 2/19/13 at 1:48pm

Keep going. I measured almost 20 volts of unclipped output from my 3009.

That's spot on. I have the schematics of my 707 and all signal processing is done in the digital domain. Output from the DACs is about 2V then the LFE channel goes through a x10 opamp so should be about 20V.

This image isn't the best illustration as I used it to show something else in an older thread. But follow the base of the magnifying glass handle right and you'll see a lone opamp symbol (triangle) which you can trace is in the LFE feed and below it it says +20dB (10x). Every other DAC channel is identical, except this one.

wow. 20V - that's nuts.
so what is the point of trying to set the gain structure around this level if in all likelihood the max audyssey calibrated output will be much lower?

That's at 0dBFS, so max output. Makes some sense in trying to stay within THX to get approval. IIRC THX sets a spec for gain for all amps to be 29dB and LFE is hotter than the main signal by 10dB (20dB voltage) so in an all THX system, it will work.
Personally I just change system gain elements to suit what I need. To drop LFE voltages 10x between pre and power means 2 5c resistors. However, I seem to recall much of the discussion around here on pre/power voltages that most seem to think they are too low and will need additional gain in between.

There isn't one as I stated before. A gain structure is merely there to maximize S/N ratios and prevent clipping. In my case my weakest link is my SMS1 at 5 volts of output before clipping, which is still near impossible to reach as the volume would need to be upped to around 28.

I can maximize gains all I want, but Aud will override that anyways so it's really a moot point. That's in my case though, and won't hold true for most people.

right, you did state this before. but many others, including Ricci and NicksHitachi, suggest that at each step the gain should be set just below clipping, which in case of your Onkyo would be at 20Vrms.

exactly. so what do you do to make sure that after Aud calibration you still utilize the amps to the fullest extend?
Edited by zheka - 2/19/13 at 6:44pm

If I followed this structure, my subs would be calibrated to 115 db's with my mains at 75.

As of right now, to calibrate even with the mains, I have to have my amp gain at 1/4, with my sub out at -12.5. Now I have bumped this up a few db's as I run hotter, but there would be no way to output 20v and get anywhere near a flat calibration. The bass would be pretty wicked though.

That's the thing; I don't need to utilize them to their full potential. It's called headroom.

This is just my opinion but I think the only reason one would have to maximize their gains is if they are running on the verge of too small of amp, or not enough drivers. Now I'm not running anywhere near the setups as a lot of the crazies on here, but 6 18's with 2500 watts in a 2100 cf space apparently is more than enough.

Now if I'm missing anything here, and am leaving output on the table; please let me know.


I'm not complaining.

As far as over riding Audyssey goes, i always set gain structure after Audyssey has done its thing. Youll want all EQ in place for that task IMO anyways.

Theres no hard and fast rule that says you MUST take the AVR sub preout all the way to clipping. In a perfect world you would. This is why gain mismatches present special conditions which require compromise. The clipping point of the AVR preout is an upper limit for the sub trim setting, anything below should work but how well, YMMV.

As pointed out by bass addict, leaving output on the table may not be a bad thing if you have a lot of headroom built into your system. However if your trying to squeeze every drop out of the amp, youll want to take it as close to clipping as you can.

just out of curiosity how far below clipping is your amp during WoW tripod emersion scene?

Bearing in mind that 20V appears to be 20Vpp, but formerly discussed was Vrms. 20Vpp = 7Vrms.

Those onks do have hot sub pre-outs fur shure. I had to use my BFD in the +4 setting to keep my 3007 from clipping the input. However this meant the output voltage was too high for my amp and I had to check that with the input attenuators.

Yeah, it almost sounds like a little confusion between gain structure vs. trying to use (get?) all the power an amp can produce. They aren't inherently the same thing.

this makes more sense now. ty

That does clarify things - I'd not seen line level outs hit that rms level before

but is not it a chicken or the eggs situation? if you adjust gain down the chain after Audyssey calibration, would not it invalidate the level matching done by Audyssey in the first place? That's where my question in post #29 comes from.

I guess it's a matter of degree. I recently discovered that, with the gain structure I had at the time, I was at -12dBFS on my NU3000DSP during the WoW tripod scene at Audyssey calibrated "reference" (0dB MVC) level. This would mean that, assuming optimistic 2kW into 4ohm load at max output, the amp was providing no more than 150W at the time, if I am not mistaken. There is no way the CHT SS-18.2 was close to the required volume with this much power.