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Asterisk: Enabling JACK connectivity to be (super-)wideband

Dennis Guse

During the summer I found that the JACK application of Asterisk (prior version 12; I used 11) only supported narrowband (8000Hhz). In general is the JACK application nothing else than two buffers incl. two resamplers (to and from JACK).

For the wideband case Asterisk was downsampling to 8000Hz handing the data to the JACK application, which resampled and handed over to JACK and vice versa.

I found that three things needed to be changed:

  1. Prevent Asterisk from downsampling to 8000Hz
  2. Dynamic buffer sizes depending on Asterisk and JACK sampling frequency
  3. Resampling parameters

After that the necessary changes were straight forward and the patch made it into Asterisk 13. The functionality can be easily backported to Asterisk 11 by just replacing apps/app_jack.c using the one of Asterisk 13. Just follow this procedure (on Debian/Ubuntu).