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Electron Frak! copy protection music
http://www.retrosoftware.co.uk/forum/viewtopic.php?f=73&t=892
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Author:  DavidB [ Sun Feb 09, 2014 11:59 pm ]
Post subject:  Electron Frak! copy protection music

The Wikipedia article about Frak! states that, in the copy protection music for the Electron version, "polyphony was achieved via 50 Hz interrupt-driven note-switching to achieve the necessary chords". I've just looked at the code for this and I don't see anything to support that, unless it's doing something very sneaky - which is, of course, quite possible. It defines envelopes and calls &FFF1 a lot, but I don't see any code that explicitly relies on a 50 Hz interrupt. Perhaps it relies on one of the OS routines to control the timing used.

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