Markus Luttenberger wrote: > I want to play multiple sounds concurrently with ALSA. The audio data is > mono and G.711 a-law encoded. I can successfully play a single source of > audio data but the sound is distorted when I try to play two sources. > > wr_buf[count] = (char) (0.5 * buf1[count]) + > (char) (0.5 * buf2[count]); A-law is a somewhat logarithmic encoding; simply adding two values with linear scale factors will not work. If both your source data and the output device use A-law, you have to decode the samples to linear PCM, add them, and encode them back. See <http://git.alsa-project.org/?p=alsa-lib.git;a=blob;f=src/pcm/pcm_alaw.c;hb=HEAD> for the algorithm that alsa-lib uses; you would use something like buf[] = s16_to_alaw((alaw_to_s16(buf1[]) + alaw_to_s16(buf2[])) / 2); If it is possible for your output device to use a linear PCM format, you might want to use that to avoid the additional encoding step. HTH Clemens _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
