Re: [Iaxclient-devel] sound issues

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

Eloy Domingos wrote:

>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
>  
>
I suppose this depends on what you're trying to do with the value 
later.  You don't get any error, for example, if you try to do this:



#include<math.h>
 
main() {
  printf("%f\n", log10(0));
}
 
Which happily works for me:

stevek@canarsie:~ $ /tmp/a.out
-inf


Most clients will use this value to show some kind of volume level 
meter.  Depending on how you implement your meters, you may or may not 
have any trouble with -infinity.. 

For example, in iaxcomm, HandleLevelEvent does this:
   if (input < LEVEL_MIN)
        input = LEVEL_MIN;
    else if (input > LEVEL_MAX)
        input = LEVEL_MAX;
    inputLevel = (int)input - (LEVEL_MIN);

to clamp the values and convert them to an integral value for display.

I'm not sure what observed problem you have with -infinity, or what you 
mean by runtime singularity error.  But even though I haven't checked 
this, and I don't remember what the particular rules are for these 
"special" floating point values, I suspect that the first conditional 
will always be true as long as LEVEL_MIN is a real number.

If this was a real problem, we could resolve it by adding 1e-99 to the 
value before we computed it's logarithm, but I'm not sure it's a real 
problem yet.

What is it that you're doing with the value in your callback?
                                                                               




>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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>  
>