Re: [Jack-Devel] Proper way to play 2 channels on the same output.

On Wed, Jun 27, 2012 at 11:32:01AM -0700, Tim Pitman wrote:

> Hi,

Hi!

> me a delay effect. This works fine on my USB DAC, but for some reason
> when I use my motherboard's audio sometimes when 2 tones (one from
> zynaddsubfx and one being repeated by my app) at the same time on the
> same channel, the sound is distorted. I have a feeling that I'm
> missing something obvious.

Clipping? That is, the sum of the two signals exceed the maximum or
minimum value? In jack, it's -1.0 .. 1.0.

So instead of simply copying the samples, multiply them with let's say
0.5 and check if the problem still exists. Or simply lower the volume in
zynaddsubfx.

Easy test setup: record zynaddsubfx and your delay output in one channel
and see if it exceeds the range. You can even write a client that simply
checks for too large values:

   for (int i=0; i < nframes; i++) {
      if (fabsf(inbuffer[i]) > 1.0) {
	 printf ("Signal too large\n"); /* bad! not RT-safe */
      }
   }


Disclaimer: don't do printf in the process() callback in production
code.


HTH

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