Date: 20 Aug 1994 00:00:01 EST

  Short answer: You don't.

  Long answer: The DSP on the Indigo is used exclusively by the audio
  system: whenever you are using the audio, you are using the DSP.

  In order to insure that audio processes are serviced, access to the DSP
  is limited to the audio device driver which performs all functions on
  behalf of application programs.

  Moreover, any code developed for the DSP on the Indigo may not work on
  other systems since the DSP is not guaranteed to be present. For
  instance, Indigo2 and Indy do not have a DSP. Audio is supported by a
  combination of code running on the CPU and a audio ASIC chip. SGI
  supports the Audio Library software inter- face as opposed to any
  particular hardware implementation of the audio system.

  Lastly, any signal processing code developed on the host CPU benefits
  from speed increases of the CPU (and this code is easier to write as
  well).