Re: [Iaxclient-devel] sound issues

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

Hi Steve,


Completely correct, log10(0) is -infinity :-). This will also give you
a runtime singularity error and break your program, so this exception
needs to be handled properly, as a well-behaved program should... :-p

Note that I have added some code to prevent this from happening in
vol_to_db(). However, I was wondering whether anyone else had the same
problem (i.e. runtime error due to log10(0)) as me.

I suspect that I am just not properly setting up the audio output_level 
or something along those lines, but I haven't been able to discover 
any irregularities with my portaudio audio setup (yet).


Eloy Domingos


On Mon, 26 Apr 2004 10:52:55 -0400, Steve Kann wrote
> 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
> >


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