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The book, "Processing : An Introduction ..." has not the chapter about sound. But the Processing website page about the book refers it. It may be a mistake from 'Copy and Paste into'! ^.^;
cf. The book, "The SparkFun Guide to Processing" has it.
Look at the minim library
Looks like the error is here:
Could you submit an issue on the docs repo -- or just correct the page and submit a pull request?