AGC - Automatic Gain Control

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Gale Andrews
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Re: AGC - Automatic Gain Control

Post by Gale Andrews » Fri Nov 02, 2012 5:33 am

steve wrote:As Nyquist effects are "below the line", would it not be possible to remove Leveller and squeeze in 2 Nyquist effects below the line?
Maybe, but I would not bet on it. If you get AGC in and it has some kind of distortion effect, then that kind of distortion is in Audacity.
steve wrote:We also get a lot of requests regarding vocal distortion effects (robot voices, monsters, airline pilots....)
Yes those sort of requests are on Wiki Feature Requests. General requests for distortion effects don't appear at all, unless you count requests for "Chorus".


Gale
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steve
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Re: AGC - Automatic Gain Control

Post by steve » Fri Nov 02, 2012 1:11 pm

Gale Andrews wrote:Yes those sort of requests are on Wiki Feature Requests. General requests for distortion effects don't appear at all, unless you count requests for "Chorus".
No I wouldn't count Chorus as a "distortion" effect.
With "Distortion" effects there is some kind of "wave shaping" going on (deforming the waveform).
Chorus is a special type of "delay" effect where the delay period changes over time: http://en.wikipedia.org/wiki/Chorus_effect
We have a good Chorus effect here (2 versions): http://forum.audacityteam.org/viewtopic ... 42&t=68007

We do see requests for general distortion effects quite frequently on the forum, but we tend to direct them to either the Leveller effect, or to VST rather than to making a feature request. Perhaps some kind of "multi-fx" plug-in could fill the gap for both vocal and instrument distortion effects, though such an effect would benefit greatly from "Preview" which is not currently available for Nyquist plug-ins.
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steve
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Re: AGC - Automatic Gain Control

Post by steve » Sat Nov 03, 2012 5:34 pm

Topic re. distortion effects split to: http://forum.audacityteam.org/viewtopic ... 41#p195841
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markh1289
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Re: AGC - Automatic Gain Control

Post by markh1289 » Tue Feb 19, 2013 8:40 pm

I tried this with default settings on a selection of a 10 seconds selection of a longer mp3. It severely distorted the time domain - it played back super slow for the selected section. Anyone else had this problem? It's on Ubuntu 10.03, Audacity 1.3.12-beta.

steve
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Re: AGC - Automatic Gain Control

Post by steve » Tue Feb 19, 2013 9:31 pm

markh1289 wrote:I tried this with default settings on a selection of a 10 seconds selection of a longer mp3. It severely distorted the time domain - it played back super slow for the selected section. Anyone else had this problem? It's on Ubuntu 10.03, Audacity 1.3.12-beta.
Please attach the plug-in .NY file so that I can see exactly which version you have. (Use the "Upload attachment" button below the message composing box).
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markh1289
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Re: AGC - Automatic Gain Control

Post by markh1289 » Wed Feb 20, 2013 10:49 am

Thanks for your response Steve.

It's from here,
http://forum.audacityteam.org/download/file.php?id=6273

... which doesn't seem like a very official place to get it from.
Is there an official repository of these plug-ins?

Opening it in Notepad,
;nyquist plug-in
;version 3
;type process
;name "Automatic Gain Control..."
;action "Applying AGC..."
;info "by Steve Daulton (http://www.easyspacepro.com).nReleased under GPL v2.n"

steve
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Re: AGC - Automatic Gain Control

Post by steve » Wed Feb 20, 2013 3:09 pm

Thanks, got it.
markh1289 wrote:... which doesn't seem like a very official place to get it from.
Most Nyquist plug-ins are user contributions. Other than the ones that are shipped with Audacity they should be thought of as "third party".
Most plug-ins are initially posted to this forum so that they can be tested and reviewed by other users. I cannot over-emphasise how important user feedback is, not only does it help to fix bugs but it also provides vital feedback for plug-in authors about how well their plug-ins work in practice. Sadly there is relatively little user feedback, which slows down the progression of plug-ins to the next stage....

After plug-ins have been thoroughly tested, and if necessary fixed or refined, they may be uploaded to the Audacity wiki. The wiki is about as "official" as plug-ins get, though they are still really "third party" plug-ins. The main wiki page for plug-ins is here: http://wiki.audacityteam.org/wiki/Downl ... t_Plug-ins

markh1289 wrote:I tried this with default settings on a selection of a 10 seconds selection of a longer mp3. It severely distorted the time domain - it played back super slow for the selected section. Anyone else had this problem?
I can't reproduce that problem.

Could you try this as a test:

1) Open Audacity
2) Generate a click track with the default settings (Generate menu: Click Track -> Tempo 120, 4 beats, 16 bars).
3) Create a new track (Tracks menu)
4) Generate a "Chirp" with the default settings (Generate menu: Chirp -> Frequency 440 / 1320, Amplitude 0.8 / 0.1 Duration 30 seconds.
5) Ctrl+A to select all.
6) Apply the AGC effect.

With the default settings in AGC you should see that the amplitude of the Chirp is substantially evened out so that the right end of the tone is almost the same amplitude as the left end. The Click track should be almost unchanged. The click tempo should be exactly the same as before.
Does that work for you?
If not, what happens?
If that does work, then what do I need to do different to reproduce the problem?
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markh1289
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Re: AGC - Automatic Gain Control

Post by markh1289 » Thu Feb 21, 2013 9:25 am

That worked fine.
I thought maybe the fact I applied AGC to a selection might have caused the time shift so I attempted to apply it to the whole imported mp3. The orange progress bar got 1/2 way then Audacity froze up. I had to force quit Audacity.
The file I'm dealing with is this one,
http://sydney.edu.au/podcasts/2012/maxine_mckew.mp3
If you download it, import it, select any eg. 10sec segment & apply AGC you get massive slow-down.
I've attached a small segment which has only had default AGC applied.
Attachments
maxine_mckew_Audacity-small segment_default-AGC.mp3
(403.05 KiB) Downloaded 498 times

steve
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Re: AGC - Automatic Gain Control

Post by steve » Thu Feb 21, 2013 11:29 am

markh1289 wrote:I've attached a small segment which has only had default AGC applied.
When I open that, the sample rate (in the information panel on the left end of the track) says 11025 Hz. Click on the name of the track and from the drop down menu select "Set Rate > 44100". The track will then playback correctly.
markh1289 wrote:If you download it, import it, select any eg. 10sec segment & apply AGC you get massive slow-down.
No, that's not happening here.

Starting from Audacity being closed, these are my steps (try this yourself and let me know if your result is different).
  1. Open Audacity
  2. "File > Import > Audio" select "maxine_mckew.mp3" and wait. The file is imported as mono, 11025Hz, 16 bit PCM.
  3. Select from 22:49 to 22:59
  4. Apply AGC, with default settings:
    AGC strength: 100
    Gain reaction speed: 1.5
    Audio source filter: Music
    Squelch threshold: -60
    Squelch attenuation: 0
My result is that the AGC effect does a remarkably good job of evening out the volume level. Playback speed is normal.
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greyham
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Re: AGC - Automatic Gain Control

Post by greyham » Fri Jan 23, 2015 10:15 pm

Hey Steve. Thanks heaps for this plugin; it's exactly what I wanted. Any chance of adding the latest version to the list in the wiki so it's easier to find?

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