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Topic: Looking for automatic gain control for line-in  (Read 1808 times) previous topic - next topic
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Looking for automatic gain control for line-in

Hi all, thanks for reading and help.

I've to record DJ sessions, the line in is directly connected to the mixer master output (and can't be connected differently for some reasons), as we suppose the DJ starts the party time playing with lower volume then in the heart of the night, as result the beginning is recorded with less bit depth resolution and it needed to be manually amplifed later.

I'm looking for a very simple tool that is able to adjust the Window's mixer record line in slider with a certain logic.. I've to set the average volume (for example -6dB) ad the time of average calculation and the time of change.. that means if I have for example the last minute playing at -20dB average, it increase the line in slider slowly till reaching -6dB, if the average becomes -4dB it reduces it slowly, and so on.

I searched for hours in Google and nothing like this exist, and I'm a bit shocked.. looks easy to do and useful.
Thank you for help.

Re: Looking for automatic gain control for line-in

Reply #1
Do you want this happening in real-time or can it be post-processed onto the recorded signal?

Re: Looking for automatic gain control for line-in

Reply #2
As a general rule, automatic volume control doesn't work very well if you want to maintain the "quality" of the recording because the AVC can't tell the difference between a quiet song, a fade-in/fade-out, or a change in the volume control.     The "worst thing" is when there is a quiet passage or a quiet song and the AVC turns-up the gain...   Then you get a sudden loud part and a bunch of distortion until the AVC turns the gain down again.   Some video cameras have AVC and it can create a real mess, especially with music.

You can speed-up the attack and release times to make it more like a regular compressor/limiter but then you compress the dynamics of the whole performance.

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as result the beginning is recorded with less bit depth resolution
Big deal...  If there are any "resolution" issues from a lower volume they are probably on the analog side (lower signal-to-noise ratio when you lower the signal).    Or if you are worried, record at 24-bits.

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I searched for hours in Google and nothing like this exist, and I'm a bit shocked..
A regular compressor might be able to do it if you can set the attack & release times slow enough.
 

Re: Looking for automatic gain control for line-in

Reply #3
Hi! you're very kind to answer me :)
by the way I probably didn't describe exactly what I'm looking for, I'm not searching for a DSP/audio signal processing, I'm just looking for a software that calculates the average and increase/reduce the slider of the mixer "line-in record". Yes real time, absolutely, the signal from the DAC will go directly into the wav file, I just need to edit the gain(volume) of the sound device analog mixer input, before it goes on the DAC.
I understand perfectly all the negative sides of this process, but for some reasons I need that.  If you're curious here are the reasons:

I'm using directsound for recording the DJ session, syncronize the lights of the club and drive a Vu-meter to check the amplitude clips. Plus directsound will drive also this software I'm looking for to change the line-in gain.
I don't want to edit manyally post the wave file for gaining where needed.
The light control software needs to detect the bpm, and it doesn't work well if the signal is too few.

If I set a target average of -6dB there will be enough space for "peaks", and if it will go in distortion for some reasons I'll not care a lot. The gain tune has to be adjusted slowly, to give you an idea in about a minute, in this way the result will be homogeneous, if the DJ lows or loud the music intentionally it will be conserved, and everything will be saved at an adeguate level.

looks strange I can't find such software..

Re: Looking for automatic gain control for line-in

Reply #4
Maybe you can give your DJ a separate house volume control (between the mixer-out and the power amps).

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looks strange I can't find such software..
You can look for a compressor plug-in that has long attack & release times.   But, it will work digitally after the ADC and your DAW/recording software will have to support real-time effects.

Or, look for a hardware compressor.    I was just "looking around" and the Behringer MDX2600 has attack times up to 300 milliseconds and release time up to 5 seconds.  That might work for you, but with hardware it's not as easy to try-before-you-buy.

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The light control software needs to detect the bpm, and it doesn't work well if the signal is too few.
The lighting effects I built don't have beat detection but they do have automatic sensitivity (based on a 20-second moving average) and they work over a wide volume range.

Re: Looking for automatic gain control for line-in

Reply #5
thank you for kind answer..
As I wrote, no one of this solution can be considered opportune in my situation. I just need something that regulate the gain of the mixer, like Skype does with microphone.. but much more slower. It's very easy, I just regret I don't know how to program in Delphi/etc to do it myself..

Re: Looking for automatic gain control for line-in

Reply #6
I'm not sure it's of use, but maybe worth a look nonetheless, and that is Rockbox has live recording functionality: Automatic Gain Control.

Whether or not a device with Rockbox installed is usable in your setup I'm unsure.

 

 
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