Math question for Digi (or anyone else)

[dBHEAD]

I know I must have a misconception somewhere. Just out of intellectual curiousity, I'm hoping somebody can answer this question:

At 24 bit resolution, Pro Tools is supposed to use 7.5 megabytes per track minute. But according to my calculations, it should be using close to 8 megabytes per minute.

If I use a sample rate of 44,100 per second, that would mean 2,646,000 samples per minute. If a byte is an eight bit digital word, each sample would require the space of 3 bytes. Times 2,646,000 samples that would mean 7,938,000 bytes per minute.

Now I know Digi wouldn't say 7.5 megabytes per minute if it was actually 7.938, so I'm just wondering where my error is.

[Chris Townsend]

dBHead, I think one source of error is that there are two common definitions of a megabyte in the computer industry. Often a megabyte is defined as 1,048,576 bytes (because it is a 'round' number in binary notation), not 1,000,000. Anyway, so 7.5 * 1,048,576 = 7864320, which is fairly close to the 7,938,000 figure that you came up with.

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Chris Townsend
DSP/DAE Engineer

[dBHEAD]

Thanks, Chris!

I didn't know about that definition of a megabyte -- just goes to show you learn something new every day!