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AGC question.

L

laAVIDtech

I have a bit of confusion about stated release times of processors and AGC's specifically.

Let's start with DBX models 1066, 166XL and the 160SL. DBX describes their release times in "db per second" ranges. Am I to guess that 3db per second would be slower than 5db per second? I was a little surprised to see the expensive 160SL's slowest release time is only 10db per second. That seems fast considering the cheap 166XL is pretty slow at 3db sec.

Other units describe release times with numbers only. For example, I am interested in a Compellor 320d by Aphex. They have two rates of release -- 3db and 10db. Am I to assume that means per second?

Can anyone guess as to what the release times would/might have been for an Audimax 4450 or the AGC circuit on a Optimod 8000?

Thanks in advance!!

John
 
laAVIDtech said:
I have a bit of confusion about stated release times of processors and AGC's specifically.

Let's start with DBX models 1066, 166XL and the 160SL. DBX describes their release times in "db per second" ranges. Am I to guess that 3db per second would be slower than 5db per second? I was a little surprised to see the expensive 160SL's slowest release time is only 10db per second. That seems fast considering the cheap 166XL is pretty slow at 3db sec.

Other units describe release times with numbers only. For example, I am interested in a Compellor 320d by Aphex. They have two rates of release -- 3db and 10db. Am I to assume that means per second?

Can anyone guess as to what the release times would/might have been for an Audimax 4450 or the AGC circuit on a Optimod 8000?

Thanks in advance!!

John
Click to expand...

Unfortunately, the dB/sec description is only useful for those units that work evenly over their range...many processors change attack and/or release rate depending upon a number of factors. Some processors change on purpose, others just aren't consistent over their operating range. Some processors even change at a linear, rather than a log (dB) rate, making a dB/sec measurement useless.

Before consistent dB/linear operation was SOP, processing timing was typically described by its time constant in seconds, milliseconds or microseconds, a single figure being used to describe the overall time it takes to go from one extreme to the other. (The theoretical formula for time constant is how much time it takes a zero value to charge to 63.2% of its final value, or for a given value to discharge to 36.8% of its original value. You can also describe it in Hz, with frequency being 1/(2*PI*T) where T is time constant). It is not a linear process, in that the timing rate changes over its range, slowing significantly as it closes in on its final value.

Complicate this further by introducing feedback and other complex dependencies into the process, and you can see how it takes more than a few paragraphs to accurately describe all the possibilities.

Kind Regards,
David
 
Thanks David!

Your explanation was understandable -- especially when I compare it to real world experience. It's why my old (and now sadly gone) Optimod 8000 sounded so much better (at least by my ear) than my current DBX units when it came to leveling performance.

Since we are chatting audio processing, I will elaborate. I use a DBX 166XL as a AGC -- medium attack, slowest possible release and about -12db gain reduction for average program levels. Following that is a DBX 1066 with faster attack, faster release but only about -6 average gain reduction and very light clipping (or "Peak-Stop" in DBX speak).

The weakest link to my ear has been the "AGC" portion of my little setup and now I understand why from your explanation. As long as the program levels are in the sweet spot, everybody is playing nice together but it seems that compression ratios and densities change audibly as soon we depart that spot.

Anyway, thanks for the overview. I have learned more in an hour of surfing this site yesterday than I had in the previous year!

John
 
John,

I don't know what you are processing for, but i use a DBX on the OUTPUT of my 12 Channel switcher for my talk station. All the programs are as level as we could get them.

I use the DBX to clean up the levels and get them consistent before they get to the Audiovault sound card. It works quite well. A little easier for me, I suppose, as I was able to trim out each channel to get them close, so the DBX is doing light duty.
 
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