Re: [Iaxclient-devel] sound issues

[Steve K. <st...@st...>]

Eloy,

    Doesn't log10(0) just give you -infinity as a result?  That is the 
correct result for us; the sound level when there's no sound is 
-infinity decibels..

-SteveK


Eloy Domingos wrote:

>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
>