Fix for Classic Audio That’s Too Fast or Too Slow

Just resolved a tech support issue that highlighted what seems to be an undocumented aspect of Mac OS X’s Classic support, in particular how it handles Classic audio.

Someone reported that suddenly all sound from Classic apps was playing slower than normal, like a 45 RPM record played at 33 1/3 (for those who remember life before CDs.) This started happening after a Mac OS X with sound input support crashed after recording a sound. All Classic applications were effected but sound produced by Mac OS X applications was just fine.

It turns out the answer was in the Audio MIDI Setup application that lives in /Applications/Utilities, in particular the Format setting of the Audio Input section for the Built-In Audio device. The crashing application left the sampling rate set to 32000Hz instead of the default value of 44100.0Hz. Resetting it back to 44100.0Hz fixes the problem.

The Mac OS X Classic support code must provide a virtual sound driver that routes all sound to the Mac OS X built-in audio source at a 44100Hz rate. When that input is set to any other rate then Classic sounds will be either speeded up (for higher rates) or slowed down (lower rates.)

One Response to “Fix for Classic Audio That’s Too Fast or Too Slow”

  1. Michael M says:

    Thank you Dave for the tip! Although I’ve never experienced this problem, (that I remember) I’ll keep this tip in mind.

    -Michael M.