Variable Speed Replay of Digital Audio with Constant Output Sampling Rate
The design of conventional analogue audio recorders permits replay over a wide range of tape speeds. This is a particularly useful feature exploited by sound editors for monitoring the tape at spooling speeds, or accurate location rock and roll at very low tape speeds. No attempt is made to equalize the replay process because adequate intelligibility can be achieved without it; and the low quality does not affect the final product. Tape speed varies from zero to up to 5 times normal speed. In contrast it is also customary to provide variable speed replay over a small range (+/- 10%) to achieve deliberate pitch change, develop special effects such as flanging, or enable synchronization with other machines. For these cases, the highest quality must be maintained since the speed change is part of the final product. This paper discusses the problem of variable speed digital audio replay from tape or disc and proposes one solution for a medium quality method suitable for edit point location in an editing system.
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