Manipulating PCM

One problem of shifting the sampling rate of a PCM sound is the intrinsic link between pitch and time. Pitch shifting upward by one octave yields a sound which plays at twice as high a pitch, and for half the time. Another problem is the so-called munchkinification ect. This relates to the apparent shift in the perceived sound-producing obj ect when the pitch and time is shifted. For example, the octave-up pitch shift also yields the perception of a talker whose head sounds half the size of a normal person. This other dimension, which has to do with the quality of sounds rather than pitch, loudness, or time, is called timbre. Once we ve learned more about the frequency domain, we ll have better tools to explain munchkimfication and timbre, and we ll also have a lot more tools to avoid (or control independently) all of these dimensions. 

As a vibration on the skin increases in frequency toward 100 Hz, it feels more andmore like a steady constant pressure. Sound, at frequencies of35, 60, and 100 Hz, is perceived increasingly as a pitch, and certainly not as individual repetitions of some event in time. The key as to how we might manipulate time in PCM samples without changing pitch and timbre lies in the time = 1/30 second transition. 

The modulations due to interference from overlap-add can be quite audible, and depending on the rate of artifact occurrence, can manifest as either a roughness or an actual pitch (overlap windows spaced every one hundredth of a second will cause a clear 100 Hz tone to be heard in the processed waveform). This can be fixed somewhat by randomizing the window rate. This usually results in a decrease in the pitchiness of the artifacts, but introduces a noisy roughness. 

4 Ouch Even More Artifacts from Overlap-Add 

Another artifact that comes from overlap-add time scaling arises because certain parts of sounds are more naturally extended or shortened in time, while 

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