Most modern CPUs use a 32 or greater register and data path and there might be some simplification in the code to perform the various DSP operations due to greater bit depth, but none of that would effect the end user. With care 24 bits is plenty to do the various data transformations without audible loss. Some extra steps might be required on a 24 bit DSP vs. 32 bit that might potentially cause it to do fewer ops per second, but either it's fast enough or it's not, so as a consumer this isn't something I'd worry about.
[This message has been edited by charlie (edited January 06, 2003).]
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Charlie