Pitch detection and intonation correction apparatus and method

A method for processing a music waveform comprising the steps of,

• sampling said music waveform at intervals of time to produce a sequence of musical representations at a sample rate of the waveform, {x.sub.j } for j=0, 1, 2, . . . i, where i represents the current sample at a current sample rate of the waveform and j=1, j=2 . . . represent prior time samples of the waveform,
• providing an estimate of lag value L.sub.est of the period of the music waveform,
• updating two functions representative of the accumulated energy of the waveform over two periods 2L of the waveform, using
• E.sub.i (L)=E.sub.i-1 (L)+x.sup.2.sub.i -x.sub.i-2L.sup.2,
• H.sub.i (L)=H.sub.i-1 (L)+x.sub.i x.sub.i-L -x.sub.i-L x.sub.i-2L, and
• selecting that lag value of L as the period of the music waveform that minimizes the difference between E.sub.i (L) and 2H.sub.i (L).

Apparatus for processing a music waveform comprising,

• means for sampling said music waveform at intervals of time to produce a music waveform sequence of numerical representations of the waveform,
• {x.sub.j } for j=0, . . . i, where
• i represents the current sample of the waveform and 0,1,2 . . . represent previous time samples of the waveform,
• means for determining the auto-correlation values of said sequence {x.sub.j } at lag values zero and L, and
• means for determining the smallest value of L which minimizes the difference between the auto-correlation at lag zero and the auto-correlation at lag L,
• whereby said smallest value of L represents the measured period of said music waveform.

Apparatus for processing a music waveform comprising,

• means for sampling said music waveform at intervals of time to produce a sequence of musical representations at a sample rate of the waveform, {x.sub.j } for j=0, 1, 2, . . . i, where i represents the current sample at a current sample rate of the waveform and j=1, j=2 . . . represent prior time samples of the waveform,
• means for providing an estimate of lag value L.sub.est of the period of the music waveform,
• means for updating two functions representative of the accumulated energy of the waveform over two periods 2L of the waveform, using
• E.sub.i (L)=E.sub.i-1 (L)+x.sup.2.sub.i x.sub.i-2L.sup.2,
• H.sub.i (L)=H.sub.i-1 (L)+x.sub.i x.sub.i-L -x.sub.i-L x.sub.i-2L, and
• means for selecting that lag value of L as the period of the music waveform that minimizes the difference between E.sub.i (L) and 2H.sub.i (L).