AGC for ADAU1761

TomY Question

Feb 15, 2013 00:00

Hello,

I'd like to implement AGC (Automatic Gain Control) for ADAU1761 or ADAU1781.

I think AGC is same as Automatic Volume Control which was in ADI tool box.
Is it correct?

And I could not find the details information of AVC.
I could find the following only.
https://wiki.analog.com/resources/tools-software/sigmastudio/toolbox/adialgorithms/automaticvolumecontrol

Could you provide the details information of AVC, please.

Best regards,

Audio Signal Processors

adau1781

SigmaDSP Audio Processors

adau1761

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KJBob Reply

Feb 17, 2013 00:00

Hi Tom,

You'll find Brett G.'s description of this module at https://ez.analog.com/message/12899#12899

I tried this algorithm on a AD1940 and found that it performs really well. The controls work nicely as labeled. The on/off switch is a bypass -- it affects the signal immediately when switched either way. The decay rate controls the time to bring a low signal upward to goal level, while the attack time for loud inputs is fixed at a fast rate. The max attenuation and gain controls allow you to choose how far the AVC will strive toward goal level. Setting a freeze level lets it ignore (and not bring up) background noise. These controls may make this AVC useful even in live sound, where a lesser algorithm would keep increasing the gain until feedback occurs.

I set up this test circuit, which shifts the AVC's input between two tone levels 20dB apart:

The envelope into the AVC appears like this:

With the AVC set as shown, its output envelope appears below:

About the difference between AVC and AGC -- often these terms are used interchangeably. Both automatically control the gain in order to level the volume.

Best regards,

Bob