Macintosh Audio Hardware - an overview

• Description: ALL Macintosh computers come with the ability to play back sounds at any sample rate (sample rate conversion is done in software.) Older machines have 8 bit stereo output (hardware runs at 22254 samples/second). The newer machines have 16 bit stereo hardare running at 44100 samples/second.

  Most of the recent Macintosh computers come with sound input hardware. There are probably exceptions to this, but the older and some of the current low-end machines have 8 bit (linear) mono hardware running at 22254.54 samples/second. All of the PowerPC, AV, and the 500 series notebook computers come with 16 bit 44kHz stereo sampling hardware. They can also record at 22050 samples/second. The sound manager implements an AGC (Automatic Gain Control) function for the 8 bit hardware. The drivers have a switch to turn off the AGC.

  There are a number of DSP vendors that support high quality audio. Generally this means quieter analog sections, and more IO formats (AES/IBU, for example). Try DigiDesign and Spectral Innovations.

  The software drivers for sound are described in "Inside Macintosh: Sound". If you want to see some sample code check out the sources for the Matlab "Sound and Image Toolbox". They can be found at

  ftp://ftp.apple.com/pub/malcolm/SoundAndImageToolbox.cpt.hqx

  Routines that play and record sounds using the toolbox are included (and interfaced to Matlab).

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