Software-emulated 3-D buffers are computationally expensive. For example, each buffer can consume about 6 percent of the processing time of a Pentium 90. You should take this into consideration when deciding when and how to use 3-D buffers in your applications.
Use as few 3-D sounds as you can, and don't use 3-D on sounds that won't really benefit from the effect. Design your application so that it's easy to enable and disable 3-D effects on each sound. You can call the IDirectSound3DBuffer::SetMode method with the DS3DMODE_DISABLE flag to disable 3-D processing on any 3-D sound buffer.
DirectSound provides a means for hardware manufacturers to provide acceleration of 3-D audio buffers. On these audio cards the host CPU consumption will not be a consideration.