[Iaxclient-devel] sound issues

[Eloy D. <elo...@vo...>]

Hi All,


Another thing which keeps bugging me is a problem with the sound system
of libiaxclient (or better portaudio). I am not sure what the real cause
for it is.

This is the problem:

In the following function from audio_encode.c, I had to build in a 
protection to avoid a singularity issue when calling the log10() function:

--- snip --- snip ----

static double vol_to_db(double vol)
{
  //
  // protect the log10 function being called with vol=0
  //
  if (vol<1e-99) vol=0.0001;
  
  return log10(vol) * 20;
}

--- snip --- snip ----

The original function just does a straight call to log10(vol) without check.

When I traced the call, I got these references of vol_to_db():

lib\audio_encode.c(32): iaxc_do_levels_callback(vol_to_db(input_level), 
vol_to_db(output_level));
lib\audio_encode.c(90): volume = vol_to_db(input_level);

In the end it turns out that the output_level=0 an awful lot of times,
causing the log10() function to blow up.

When I trace the setting of the output_level var, I get these references:

lib\audio_encode.c(7): static double input_level = 0, output_level = 0;
lib\audio_encode.c(103): calculate_level((short*)audio, len, &output_level);

The calculate_level function is called to set both input_level and 
output_level, and is using the audio stream's data:

--- snip --- snip ---

static void calculate_level(short *audio, int len, double *level) {
    short now = 0;
    double nowd;
    int i;

    for(i=0;i<len;i++)
      if(abs(audio[i]) > now) now = abs(audio[i]);

    nowd = now/32767;   // note: this seems useless to me

    *level += (((double)now/32767) - *level) / 5;
}

--- snip --- snip ---

Which would suggest that the audio output can be zero, but the output_level
is still being calculated. For some reason, the input_level does not seem
to suffer from the same effect.

When I enable the log10() safeguard, the softphone is fully functional,
without the safeguard, you cannot run the program due to the runtime
problem of doing a log10(0).

Has anyone seen this problem before? Can it be avoided by certain actions or
audio settings?


Best regards,
Eloy Domingos