Speex dev - Jan 2014 - Some Speex AGC Questions

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?

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.)

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

Thanks,

Ken
Kenneth Lerman

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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