slipstretch is a simple experimental audio stretching algorithm that splits the audio stream up into frequency bands before stretching them. Then, it stretches each frequency band separately. This allows higher frequencies to use a smaller window/chunk size, reducing transient1 flutter2/flam3 artifacts. The one cross-band constraint4 is that lower frequency bands are not allowed to timeshift further "left" than higher frequency bands, which reduces bass smearing5.
The underlying audio stretching algorithm after splitting the audio stream up into frequency bands is very simple, so it doesn't sound very good. If a better underlying algorithm were used, then this would be much better.
0.75x and 1.5x pitch shift music example (make sure to unmute it):
2023-10-02_22-28-59.mp4
110% time stretch music example (multiband -> fullband -> original) (make sure to unmute it):
music.example.mp4
For more, see the examples directory.
Footnotes
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transient -> when you have click or tap or smash sounds instead of smooth rise/fall ↩
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flutter -> warble but in high frequencies instead of low ↩
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flam -> what drummers call it when you get two transients right next to eachother instead of lined up on top of each other ↩
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cross-band constraint -> not jargon, means what the individual parts mean, it's a constraint applied across frequency bands when doing the time shifting ↩
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bass smearing -> when bass frequencies of drums come before their high-frequency attack instead of after; sounds really bad ↩