Timestretching
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Timestretching, time stretching, timescaling or pitch control is the process of changing the speed or duration of an audio signal without affecting its pitch.
Its primary use is in electronic music and remixing to alter samples. It can also be used by musicians who might wish to study a fast passage of music by slowing it down, yet having the pitch of the notes stay the same.
The function is found in both software and hardware applications. It first appeared in MP3 players with the introduction of Creative Labs' Nomad Jukebox. In hardware applications timestretching is effected by using a DSP (Digital Signal Processor) on the motherboard of the MP3 player. There is often a choice of several playback speeds, either faster or slower.
Timestretching is sometimes offered through something called playback speed control, although this isn't true timestretching. Instead, it alters both the speed and the pitch.
Time stretching is often used to adjust Radio commercials [1] and the audio of Television advertisements[[2]] to fit exactly into the 30 or 60 seconds available. (A telecine pulldown pattern adjusts the video).
Time stretching can be used with audio books and recorded lectures. Slowing down may improve comprehension of foreign languages[3].
While one might expect speeding up to reduce comprehension, Herb Friedman says that "Experiments have shown that the brain works most efficiently if the information rate through the ears--via speech--is the "average" reading rate, which is about 200-300 wpm (words per minute), yet the average rate of speech is in the neighborhood of 100-150 wpm." [4]
Speeding up audio is seen as the equivalent of "speed reading" [5] [6].
