[pulseaudio-discuss] [PATCH v3 11/24] echo-cancel: Start capture at a sane value if we're doing webrtc AGC

[Tanu Kaskinen]

On Mon, 2016-01-18 at 13:06 +0530, arun at accosted.net wrote:
> From: Arun Raghavan <git at arunraghavan.net>
> 
> This is required to make sure the capture output has sufficient energy
> for the AGC to do its job.

I think the word "value" in the first line of the commit message should
be replaced with "volume". After reading just the commit message, I
didn't know what the patch was about.

> ---
>  src/modules/echo-cancel/echo-cancel.h |  1 +
>  src/modules/echo-cancel/webrtc.cc     | 14 +++++++++++++-
>  2 files changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/src/modules/echo-cancel/echo-cancel.h b/src/modules/echo-cancel/echo-cancel.h
> index 142f8ac..b570095 100644
> --- a/src/modules/echo-cancel/echo-cancel.h
> +++ b/src/modules/echo-cancel/echo-cancel.h
> @@ -68,6 +68,7 @@ struct pa_echo_canceller_params {
>              pa_sample_spec sample_spec;
>              bool agc;
>              bool trace;
> +            bool first;
>          } webrtc;
>  #endif
>          /* each canceller-specific structure goes here */
> diff --git a/src/modules/echo-cancel/webrtc.cc b/src/modules/echo-cancel/webrtc.cc
> index c2585a8..6431651 100644
> --- a/src/modules/echo-cancel/webrtc.cc
> +++ b/src/modules/echo-cancel/webrtc.cc
> @@ -52,6 +52,7 @@ PA_C_DECL_END
>  #define DEFAULT_TRACE false
>  
>  #define WEBRTC_AGC_MAX_VOLUME 255
> +#define WEBRTC_AGC_START_VOLUME 85
>  
>  static const char* const valid_modargs[] = {
>      "high_pass_filter",
> @@ -297,6 +298,7 @@ bool pa_webrtc_ec_init(pa_core *c, pa_echo_canceller *ec,
>      ec->params.priv.webrtc.sample_spec = *out_ss;
>      ec->params.priv.webrtc.blocksize = (uint64_t)pa_bytes_per_second(out_ss) * BLOCK_SIZE_US / PA_USEC_PER_SEC;
>      *nframes = ec->params.priv.webrtc.blocksize / pa_frame_size(out_ss);
> +    ec->params.priv.webrtc.first = true;
>  
>      pa_modargs_free(ma);
>      return true;
> @@ -354,7 +356,17 @@ void pa_webrtc_ec_record(pa_echo_canceller *ec, const uint8_t *rec, uint8_t *out
>      apm->ProcessStream(&out_frame);
>  
>      if (ec->params.priv.webrtc.agc) {
> -        new_volume = apm->gain_control()->stream_analog_level();
> +        if (PA_UNLIKELY(ec->params.priv.webrtc.first)) {
> +            /* We start at a sane default volume (taken from the Chromium
> +             * condition on the experimental AGC in audio_processing.h). This is
> +             * needed to make sure that there's enough energy in the capture
> +             * signal for the AGC to work */
> +            ec->params.priv.webrtc.first = false;
> +            new_volume = WEBRTC_AGC_START_VOLUME;

This is done only on initial loading of the module. Does AGC work ok
after resuming a suspended source?

-- 
Tanu