Sound Definitions

Techniques : pitch shifting : pitch scaling

These techniques can also be used to scale the pitch of an audio sample while holding speed or duration constant. Note that the technique can be called pitch scaling or pitch shifting, depending on perspective.

Musical pitch

Under one definition of musical pitch, pitch is defined as the logarithm of frequency; as the musical pitch is shifted linearly (shifting every note up the scale by a perfect fifth, for instance), the frequencies of the signal are actually being scaled, because of the logarithmic relationship between the notes we hear and the actual frequencies of those notes.

Non musical pitch scaling

A frequency shift, which is performed by amplitude modulation, does not preserve the ratios of the harmonic frequencies that determine the sound's timbre, and is not a "musical" transformation. Similarly, a literal pitch scaling, in which the musical pitch is scaled (a higher note would be shifted at a greater interval than a lower note) is highly unusual, and not musical. However, "pitch" can also be used to refer to frequency, and the other two transformations are not commonly used, so either term usually refers to musical pitch shifting.

Results of pitch adjustments on voice

Time domain processing works much better here, as smearing is less noticeable, but scaling vocal samples distorts the formants into a sort of Alvin and the Chipmunks-like effect, which may be desirable or undesirable. To preserve the formants and character of a voice, you can analyze the signal with a channel vocoder or LPC vocoder plus any of several pitch detection algorithms and then re synthesize it at a different fundamental frequency.

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