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How to Properly Set AGC

C

cc333

I'm wondering if anyone can help with this.

I have enabled AGC in Stereo Tool so the volume will be a bit more consistent, but I'm having trouble finding settings that sound fairly transparent.

Right now, I have it set to two-band mode with default settings except I have drive set to +15.0 dB, and attack and release for the second band (everything above 2000 Hz) are 200ms and 750ms, respectively.

Thanks,

c
 
cc333 said:
I have enabled AGC in Stereo Tool so the volume will be a bit more consistent, but I'm having trouble finding settings that sound fairly transparent
Click to expand...
Analog compression is the opposite of transparent. Aggressive AGC is incredibly annoying to listen to.

The attack and decay times you have listed seem extremely excessive to me. I haven't messed with radio processing in 10-15 years, but I seem to remember times being in the range of like 5 to 50 ms.

When dealing with processors, I highly recommend starting from a preset and tweaking from there. Learning the jargon in stereo tool from first principles is not a good use of anyone's time.
 
cc333 said:
I'm wondering if anyone can help with this.

I have enabled AGC in Stereo Tool so the volume will be a bit more consistent, but I'm having trouble finding settings that sound fairly transparent.

Right now, I have it set to two-band mode with default settings except I have drive set to +15.0 dB, and attack and release for the second band (everything above 2000 Hz) are 200ms and 750ms, respectively.
Click to expand...
This is a case where logic works better than any detailed "tech specs".

AGC is intended to avoid very low levels that will make a radio station... particularly in in-car listening... be buried in the road and background noise. The idea on one side is to artificially increase the levels no matter what the original producer of a song wanted or no matter what the levels are in a news report. On the other, the idea is to reduce anything that averages too much above the average level you want.

An AGC should work like a very good board operator. The approach should be humanized, so that you are simply adjusting the levels to make the sound neither too soft nor too loud. AGC is not a compressor nor a peak limiter. It's purpose is to avoid annoying listeners with audio that goes up and down, wildly sometimes, in volume between different elements.

And, with AGC, you don't want to pull up background noise, like, for example, the air conditioner in a studio during pauses in a person talking. So AGC has to be set so it works on average levels and not on very brief interludes of very low levels, like the pauses in speech. And its "threshold" (every device has an equivalent) set so that it does not amplify unwanted content.

Same goes for "loud" bits of audio. AGC should gently control levels... you don't want to compress the audio, just automatically ride gain. Your ear and a careful watch on a good VU meter (not just flashing LEDs) so you can set the dynamic range and the "feel" of the audio to your satisfaction. In such cases, having more than one person present helps.

And on that subject of "different strokes for different folks" you have to have both men and women and younger and older present.
 
With the StereoTool AGC, I tend to find leaving a 3dB window helps enormously, as it means that it isn't hunting around all the time. For most tracks it settles to a particular value and sits there.
 
Thank you all for the responses!

I set the attack and release much shorter, 25 and 50 ms, respectively, and it sounds significantly better, but still a little bit restless sometimes, so I'll set the window to 3dB and see how that sounds.

I also set the max attack and release speeds to 7dB/s and 14dB/s, which helps even it out a bit, too.

Another thing I did was set the Low Level Boost (or LLB, which in StereoTool is implemented as basically an inverse AGC) to compliment the AGC, so they work in tandem to keep the volume fairly consistent (the LLB brings it up when it gets quiet, and the AGC brings it down when it gets loud).

c
 
There are multiple examples here of settings in recording studio audio processing apps. Stations used devices intended to control modulation and audio density, and are not precisely the same as what is desired when recording audio in a studio to a disk drive.
 


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