Trying to use portaudio to record some data, then use an algorithmic filter to change the recorded voice and then play it back. I've verified a lot of it (coming from example) but I'm quite new to C and I think in my filter implementation I've done something silly.
#if LOW_PASS
{
float RC = 1.0/(CUTOFF*2*3.14);
float dt = 1.0/SAMPLE_RATE;
float alpha = dt/(RC+dt);
float filteredArray[numSamples];
filteredArray[0] = data.recordedSamples[0];
for(i=1; i<numSamples; i++){
filteredArray[i] = filteredArray[i-1] + (alpha*(data.recordedSamples[i] - filteredArray[i-1]));
}
data.recordedSamples = filteredArray;
}
#endif
#if HIGH_PASS
{
float RC = 1.0/(CUTOFF*2*3.14);
float dt = 1.0/SAMPLE_RATE;
float alpha = RC/(RC + dt);
float filteredArray[numSamples];
filteredArray[0] = data.recordedSamples[0];
for (i = 1; i<numSamples; i++){
filteredArray[i] = alpha * (filteredArray[i-1] + data.recordedSamples[i] - data.recordedSamples[i-1]);
}
data.recordedSamples = filteredArray;
}
#endif
When the recorded signal tries to go through these filters I get something the following error:
*** glibc detected *** ./paex_record: free(): invalid pointer: 0xbfd68600 ***
======= Backtrace: =========
/lib/i386-linux-gnu/libc.so.6(+0x75ee2)[0xb75e2ee2]
./paex_record[0x8048fe5]
/lib/i386-linux-gnu/libc.so.6(__libc_start_main+0xf3)[0xb75864d3]
./paex_record[0x80487f1]
======= Memory map: ========
08048000-0804a000 r-xp 00000000 08:05 2363767 /home/svictoroff/Documents/CompArch/portaudio/examples/paex_record
...
bfd68000-bff1a000 rw-p 00000000 00:00 0 [stack]
Aborted (core dumped)
I'm just really not sure what's going on here. Any thoughts? Free is called from the end of the script at terminate here:
Pa_Terminate();
if( data.recordedSamples ) /* Sure it is NULL or valid. */
free( data.recordedSamples );
if( err != paNoError )
{
fprintf( stderr, "An error occured while using the portaudio stream\n" );
fprintf( stderr, "Error number: %d\n", err );
fprintf( stderr, "Error message: %s\n", Pa_GetErrorText( err ) );
err = 1; /* Always return 0 or 1, but no other return codes. */
}
return err;
The problem is that data.recordedSamples now (at the time of free()
) points towards a structure allocated on the stack, not on the heap!
Since you had this instruction:
data.recordedSamples = filteredArray;
The
if( data.recordedSamples )
is of no use, since the adress id valid, but not consistent: it is never allocated with malloc()
and it is not on the heap, but on the stack!
At the moment when you are calling free()
, that adress could well point towards the stack of another function.
Copy your filtered data back over the original recordedSamples
if you want, just do not re-assign that pointer.
edit:
use this:
for(i = 0; i<numSamples; i++) {
data.recordedSamples[i] = filteredArray[i];
}