Re: [LAD] Regarding amplifying a PCM frame

On Mon, 2009-10-26 at 15:05 -0700, Drip Stone wrote:
> Hi,
>
> Thank you for providing valuable information. I will put some code
> here:
>
> while ( 1 )
> {
> for ( int i = 0; i < frames; i++ )
> {
> float t = 0;
> if ( left ) //for left channel
> {
> t = *((float*)&(fbuffer[pos+i*4])); //4 bytes each
> frame
> t*=2;
> //printf("%f ",t);
> for ( int j = 0; j < 4; j++ )
> buffer[i*8+j] = ((char*)&t)[j]; //8 bytes for 2
> channels
> }
>
> rc = snd_pcm_writei ( handle, buffer, frames );
> pos += frames * 4;
> }
>
> I think the value is not out of [-1.0,1.0]. BTW, what does it mean
> when a value is negative?
>
Ouch, you're doing a byte-by-byte copy of a 32bit float?? Please, just
use the correct data types.

Floating point audio data is usually signed, so -1.0 and 1.0 are the
farthest extents, and 0.0 would be the default no-signal state.

Peter.

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Received on Tue Oct 27 04:15:01 2009