[Speex-dev] Some Speex AGC Questions

[Tristan Matthews]

Hi Kenneth,

On Wed, Jan 8, 2014 at 3:09 PM, Kenneth Lerman <lerman-speex at se-ltd.com>wrote:

>
> I'm attempting to use speex preprocess for automatic gain control in an
> application I'm working on and could use some help.
>
> I'm using Opus as my codec. In order to keep the number of packets down,
> I'm using 60msec frames. I'm sampling at 48KHz as is recommended for Opus.
>
> So, the frame length is 2880 samples and the sampling rate is 48000. The
> source of the data is a microphone using ALSA. That platform is Ubuntu.
> The version of speex is 1.2rc1.
>
> When I run with the default settings, the audio seems OK. It's not clear
> if preprocess is actually doing anything.
>
> If I turn AGC on, the sound level becomes almost inaudible.
>
> When I print the control parameters (the defaults), I get:
> DENOISE = 1
> AGC = 0
> AGC_LEVEL = 1174011904
> AGC_INCREMENT = 12
> AGC_DECREMENT = -40
> AGC_MAX_GAIN = 30
> VAD = 0
> DEREVERB = 0
> NOISE_SUPPRESS = -15
>
> QUESTION number 1: Is there a guide to "tuning" the AGC? Is there a
> document that tells what they really mean and how to adjust them?
>

You might want to try calling SPEEX_PREPROCESS_SET_AGC_TARGET,
like so:
int target = 16000;
speex_preprocess_ctl(state, SPEEX_PREPROCESS_SET_AGC_TARGET, &target);



>
> QUESTION number 2: I see that VAD, DEREVERB, DENOISE, ... have values of
> 0 or 1. The documentation says that 1 means ON and 2 means OFF.  Can
> someone explain the apparent discrepancy, please? (I assume that AGC = 0
> means that AGC is off.)
>

This is a typo in the documentation, it has since been fixed (but not
pushed online I guess):
http://git.xiph.org/?p=speex.git;a=commitdiff;h=6da046b6c1afbe11f4efead4723df6a9f04d2097


>
> QUESTION number 3: Is there an easy way to search the archives of this
> list?
>

Append "from site:http://lists.xiph.org/pipermail/speex-dev/" to your
search.

Best,
Tristan

-- 
Tristan Matthews
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