Epoch manipulation

One of the key steps in both TD-PSOLA and FD-PSOLA is proper manipulation of the epochs. First, an epoch detector of the type described in Section 12.7.2 is used to find the instants of glottal closnre. This results in the analysis epoch sequence T = (tj, tl, th). From this, the local pitch period at any epoch can be found. A simple means of determining this is just to measure the distance between the previous and next 

The limits of n in the above are proportional to twice the local analysis pitch period. 

a set of synthesis epochs T = (rf,. .., is created from the FO and timing 

A mapping function M[i ] is then created. The job of the mapping function is to specify which analysis flames should be used with which synthesis epoch. We should note at this 

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Figure 14.3 Pitch manipulation with PSOLA. A new set of synthesis epochs that are spaced further apart than the analysis set is created. When the frames are overlapped and added, the new pitch is now lower due to the wider frame spacing.

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