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Author Topic: Proper gain structure  (Read 10818 times)

Steve Babine

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Proper gain structure
« on: September 03, 2013, 02:00:45 PM »

OK I have to beat this dead horse to prove a point to someone or to teach me something new. I have a guy that is telling me to turn my amps all the way up even tho we get the red clip light. His solution to this is to turn everything else down to avoid this clipping. He went as far as to turn our wireless mic's down so far that we have to run the amps at full and also our board trim's at almost full. Please correct me if I am wrong but, I was always taught to  set your gain structure by turning up your wireless mics so your in the yellow at the loudest point and adjusting the rest of the signal chain from there. Am I wrong?
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Justice C. Bigler

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Re: Proper gain structure
« Reply #1 on: September 03, 2013, 02:36:02 PM »

Which point of the gain structure are you talking about? Per your wireless mics, are you talking about the output attenuation on the wireless mic (transmitter/receiver) or on the input gain on the console for the channel that your wireless mics are patched into?

If I turned the input gain on my channel strips up until the meters were in the yellow, my faders (on both input and output) wouldn't go above about -30 on the fader strip.

Sometimes it's better to turn the input gain down and have more room to move the fader than it is to saturate the mic pre at the very beginning of the input to the gain structure. As for the amps, again it depends. I often find myself turning the gain knobs on the amps down so I can get more play out of the faders on the console before hitting the feedback threshold.

As with most thing in audio, the answer is most likely: it depends.
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Justice C. Bigler
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Re: Proper gain structure
« Reply #2 on: September 03, 2013, 02:55:11 PM »

Set up each stage in your overall signal chain such that the noise floor is as low as possible with each device/control.
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Jordan Wolf

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Re: Proper gain structure
« Reply #3 on: September 03, 2013, 02:59:36 PM »

OK I have to beat this dead horse to prove a point to someone or to teach me something new. I have a guy that is telling me to turn my amps all the way up even tho we get the red clip light. His solution to this is to turn everything else down to avoid this clipping. He went as far as to turn our wireless mic's down so far that we have to run the amps at full and also our board trim's at almost full. Please correct me if I am wrong but, I was always taught to  set your gain structure by turning up your wireless mics so your in the yellow at the loudest point and adjusting the rest of the signal chain from there. Am I wrong?
Steve,

You and your friend should read up on gain structure.  There isn't one way to go about it, and there's always a compromise, but there are certain benefits for each method.  Chuck McGregor explains in detail.  Read up, try putting it into practice, and hopefully you can both learn something.

Two examples from my job:

I work in corporate AV; normally, since I am very close to the audience, the systems I setup and use must be very quiet when there is nothing passing through them - no hissing or noise.  Because of this fact, I tend to keep the amps "turned down" as low as necessary, but not so low that I clip the input side of the amp.

If the loudspeakers are flown or further away from the audience, I can change my method a little, sacrifice that low noise floor, and achieve a higher SPL from the loudspeakers.

Overall, however, since I tend to work with very dynamic signals (the human voice…of various people, skilled and unskilled in public speaking) I always make sure I have headroom upstream of the speaker amp(s)…my wireless kits' meters are usually in the green, with occasional flickers on the yellow LEDs; my channel PFLs are around -10dB to +4dB; my main outs are calibrated so that one look at them lets me know how much headroom I have left…before feedback, clipping, or whatever I set my reference point to.
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Jordan Wolf
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Steve M Smith

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Re: Proper gain structure
« Reply #4 on: September 03, 2013, 03:04:51 PM »

Using your example of the wireless mic turned down and the input gain almost full - The input gain is turned up to compensate for the very low output coming out of the receiver.

Whilst this will work, it will also amplify any noise in the receiver's output stage.

Much better to start with it at a reasonable level.  e.g. about 3/4 of maximum then adjust the input gain to suit.


Steve.
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John Roberts {JR}

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Re: Proper gain structure
« Reply #5 on: September 03, 2013, 03:07:16 PM »

Yawn... if there was only one way to do this they would not put knobs on power amps.

#1... R&R mode... amps WFO. This way you get to take full advantage of extra headroom from internal amp clip limiters. If amps are turned down, the preceding path will clip, long before you get any extra headroom benefit from the amp limiting (technically this isn't real headroom but it sure seems like it).

#2...  "Church Mouse" mode. Sending a hot signal to the amp and trimming it down there improves the overall signal to noise including from questionable equipment interfaces. This is more notable in quiet venues (like churches) with high efficiency loud speakers.   

The reason we put knobs on power amps is because the customers are always right... even when...   :o

Design engineers invest a great deal of effort to make equipment work well together despite what the customers believe it good practice. Mostly the gear is flexible enough to work more than one way and deliver acceptable performance.

Do you have a specific audible problem or are you arguing about some feared outcome? 

JR
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Luke Geis

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Re: Proper gain structure
« Reply #6 on: September 03, 2013, 03:40:25 PM »

this is a big can of worms really....... There are many schools of operation, all of which will work..........BUT: The best one is the one where all pieces of equipment are set so they operate at the same metering point from one end to the other. When the mixer hits red so does everything else. This should ensure the best signal to noise ratio, lowest noise floor and still achieve maximum levels of potential gain. As for different styles of running a mixer that is the big debate. Some like hot head amps, some cold, while others like double bussing things and others that run the master fader really low and keep the channel faders high.
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John Roberts {JR}

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Re: Proper gain structure
« Reply #7 on: September 03, 2013, 03:50:35 PM »

this is a big can of worms really....... There are many schools of operation, all of which will work..........BUT: The best one is the one where all pieces of equipment are set so they operate at the same metering point from one end to the other. When the mixer hits red so does everything else. This should ensure the best signal to noise ratio, lowest noise floor and still achieve maximum levels of potential gain. As for different styles of running a mixer that is the big debate. Some like hot head amps, some cold, while others like double bussing things and others that run the master fader really low and keep the channel faders high.

While neat and orderly, I just posted why that gain structure negates completely any benefit from having the clip limiter feature inside power amps. Additionally the amp will clip at different voltages after the mains voltage sags so it is impractical to even try to make them all clip exactly the same.

Not so much a can of worms as a non-issue for many equipment combinations. The only can of worms is for defending only one way of doing it.

I repest my question for the OP, "Is there an audible problem he needs to correct?
 
JR
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Ron Hebbard

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Re: Proper gain structure
« Reply #8 on: September 04, 2013, 05:57:11 AM »

While neat and orderly, I just posted why that gain structure negates completely any benefit from having the clip limiter feature inside power amps. Additionally the amp will clip at different voltages after the mains voltage sags so it is impractical to even try to make them all clip exactly the same.

Not so much a can of worms as a non-issue for many equipment combinations. The only can of worms is for defending only one way of doing it.

I repest my question for the OP, "Is there an audible problem he needs to correct?
 
JR

John;

Job's patience pales in comparison to yours, I know you know of which Job I write.  You're ever the gentleman and we don't tell you often enough how fortunate we are that you're here.

Thank you.

Toodleoo!
Ron Hebbard
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Ivan Beaver

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Re: Proper gain structure
« Reply #9 on: September 04, 2013, 07:45:37 AM »

OK I have to beat this dead horse to prove a point to someone or to teach me something new. I have a guy that is telling me to turn my amps all the way up even tho we get the red clip light. His solution to this is to turn everything else down to avoid this clipping. He went as far as to turn our wireless mic's down so far that we have to run the amps at full and also our board trim's at almost full. Please correct me if I am wrong but, I was always taught to  set your gain structure by turning up your wireless mics so your in the yellow at the loudest point and adjusting the rest of the signal chain from there. Am I wrong?
If your friend thinks that he can do anything to get more out of the system "up stream" besides a little bit of compression-then he is mistaken.

The amp limit (clip) is the MAXIMUM that is available from the system-Nothing can change that.

"Proper gain structure" is ususally refered to as getting the most DYNAMIC range out of a system.  You notice I said RANGE.  The Maximum is already set by the amp.  So the ONLY thing you can do is to lower the minimum-or the noise floor.

But it DOES NOT get any louder-it only get "quieter".

In most cases the noise floor simply doesn't matter-unless it gets real high.

Now there are few other meanings of "proper".  One in which a particular level on the board equals the max out of the system-so that you have a visual indicator.

And the other is that a particular level on the board is equal to a target SPL.  Again-just a vsual indicator.

But both of these are going to have a higher noise floor than when set up "properly".

But it won't get any louder.  If you want louder-buy a bigger system-simply as that.

There is no "magic combination" of settings that will get it any louder.
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Ivan Beaver
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Re: Proper gain structure
« Reply #9 on: September 04, 2013, 07:45:37 AM »


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