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Some questions about AGC
https://forums.stereotool.com/viewtopic.php?t=4827		 Page 1 of 2
Author:  \_/ [ Tue May 21, 2013 6:47 pm ]
Post subject:  Some questions about AGC
Hi everybody!

How are the up- and downspeeds for the AGC computed? E.g. if for 1 db rise you want it to go down 0.8 db per 200 msec, does this mean you need to enter 1000/200*0.8 = 4?

I want all overshoots to be handled by the post AGC compressor. How can I turn off the jump protection (set it to 0?)? How can "remove above" be deactivated?

If the AGC goes from yellow to red, what does this mean? Just an overshoot or limiting, etc?

Thanks a lot. :)

PS db/sec/(6 db) = 1/6 1/sec isn't a valid unit. :ugeek:
Author:  hvz [ Tue May 21, 2013 11:22 pm ]
Post subject:  Re: Some questions about AGC
About valid unit: I know... :(

Your calculation looks correct.

To turn things off, just use maximum settings. That should nearly completely turn everything off.
Author:  \_/ [ Sun Jun 23, 2013 3:00 pm ]
Post subject:  Re: Some questions about AGC
Thanks, Hans.
One more: What do the 6 dB mean? The speed is already given by dB/sec, so what additional information is provided by it?
Author:  hvz [ Sun Jun 23, 2013 9:04 pm ]
Post subject:  Re: Some questions about AGC
Speed depends on the difference in level. So, if the value is 6 dB/s / 6 dB, if the difference is 12 dB the value will change with 12 dB/s.

I know x dB / 6 dB can be scratched, so the actual unit would be /s, or Hz, but that doesn't sound too logical either.
Author:  \_/ [ Tue Jun 25, 2013 9:41 am ]
Post subject:  Re: Some questions about AGC
What I'm trying to do is to compare some AGCs (and compressors) and I really have a hard time doing so because of the different specifications they use.

They usually use an expander/compressor combination so they have a ratio and a constant speed (well, apart from knee, of course). How can I mimic such behaviour?

Your example essentially says that 100% of the dB-changes are corrected per second. My example is wrong then, a factor of 6 (actually 20 log10(2), I guess) would be needed:

1000/200*0.8*6 = 24

However that would be much too fast because speed increases (linearly?) with greater distance from target. So maybe I should divide by the maximum distance to make it the maximum speed or by half the maximum distance to make it fit on average?
Author:  hvz [ Tue Jun 25, 2013 11:51 am ]
Post subject:  Re: Some questions about AGC
Quote:
Your example essentially says that 100% of the dB-changes are corrected per second.
No, that's what happens per sample. However since the difference is reduced at each sample it slows down quickly!
Quote:
However that would be much too fast because speed increases (linearly?) with greater distance from target.
That is correct. But as I said, the difference decreases with each step. So the speed drops rapidly. Which is usually exactly what you want (you don't want to HEAR it drop over a longer period of time).
Quote:
So maybe I should divide by the maximum distance to make it the maximum speed or by half the maximum distance to make it fit on average?
That's too much. Have to think a bit here.... :shock:
Author:  Bojcha [ Tue Jun 25, 2013 2:51 pm ]
Post subject:  Re: Some questions about AGC
Speeding up on bigger difference can sometimes be very bad. In my last presets i am using slower and slower 'down speed" and even then sometimes down speed is so fast. That's also present in MB. So track like "we are the champions" will never sound good.
Author:  hvz [ Tue Jun 25, 2013 3:43 pm ]
Post subject:  Re: Some questions about AGC
In MB you can turn this off! But I think it sounds worse then (except some exceptions such as We are the Champions indeed).
Author:  \_/ [ Wed Jul 03, 2013 12:09 pm ]
Post subject:  Re: Some questions about AGC
So far, so good.
Because the AGC doesn't have a ratio, does that mean that always 100% correction is applied with the only limitation beeing speed?
Author:  hvz [ Wed Jul 03, 2013 1:59 pm ]
Post subject:  Re: Some questions about AGC
Yes.
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