This is 06_Play_Through_DSP.rtf in view mode; [Download] [Up]
Written by J. Laroche at the Center for Music Experiment at UCSD, San Diego California. December 1990. Playing sounds through the DSP. It's possible to set-up a stream from the memory through the DSP to the DACs. The sound is then played after being processed by the DSP. This is usefull for real time sample rate conversion, real time reverb etc... There is an example showing how to do that in Examples/04_Through_DSP. There are problems associated with that. · First of all, if you don't use DMA, the driver might not be fast enough to keep up with the DACs. That is, the driver might not be able to send enough samples per seconds to satisfy the DACs, and clicks or drop-outs are likely to happen. This is especially true if you use 44100 stereo. Normal (non-DMA) transfer seems to be fast enough for 44100 mono, or 22050 stereo etc... I haven't been able to make 44100 stereo work reliably on a 86030 with the 2.0 system version. if you use DMA, things improve. DMA from the host to the DSP is available in release 2.0 only, and an example is given in 07_DMA_To_DSP. · Second, how can you pass controlling values (volume, amount of pitch etc...) to the DSP and avoid collisions with the sample stream to the DSP? There is no easy way (that I know of.) Therefore, for all the cases where you need some control over the DSP, you should prefer DMA.
These are the contents of the former NiCE NeXT User Group NeXTSTEP/OpenStep software archive, currently hosted by Netfuture.ch.