Linear Prediction PSOLA

The above technique bears some similarities to the TD-PSOLA technique in that it uses a pitch-synchronous analysis to isolate individual pitch periods, after which modification and resynihesis is performed. In fact in a technique called linear prediction pitch synchronous overlap and add or LP-PSOLA, we can use the PSOLA more or less directly on the residual rather than the waveform. As above, epoch detection is used to find the epochs. The residual is then separated into a number of symmetrical frames centred on the epoch. Pitch modification is performed by moving the residual frames closer or further away, and duration modification is performed by duplication or elimination of frames, in just the same way as in TD-PSOLA. The only difference is that these operations are performed on the residual which is then fed into the LP filter to produce speech. This technique differs only from the Hunt technique in the shape of the frames. Both techniques uses window functions with their highest point at the epoch in Hunt s technique the windows are asymmetrical with the idea that they are capturing a single impulse, in LP-PSOLA the windows are symmetrical. In listening tests, the two techniques produced virtually identical quality speech. 

A number of other refinements on residual excited LP have been proposed. Hirai et al [203] proposed a technique fairly similar to Hunt s which performs a particular type of manipulation on the residual before using it to excite the filter, and a number of studies have attempted to find an LP analysis technique which gives a parameterised source rather than simply a residual [336] 

Chapter 14. S Tithesis by Concatenation and Signal Processing Modification 

In addition to these advantages we also have the possibility to modify the spectral characteristics of the units. One use of this would be to ensure that the spectral transitions at diphone joins are completely smooth. While careful design and extraction of the units from the database should help ensure smooth joins, they can t always be guarenteed, and so some spectral manipulation can be useful. 

Recall in our introduction to signal processing, we saw that we could use the Fourier series to generate any periodic signal from a sum of sinusoids (Section 10.1.2). 

The above technique bears some similarities to the TD-PSOLA technique in that it uses a pitch-synchronous analysis to isolate individual pitch periods, after which modification and resynthesis are performed. In fact, in a technique called linear-prediction pitch-synchronous overlap and add or LP-PSOLA, we can use PSOLA more or less directly on the residual rather than on the waveform. As above, epoch detection is used to find the epochs. The residual is then separated into a number of symmetrical frames centred on 

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The family of techniques known as sinusoidal models use this as their basic building block and performs speech modification by finding the sinusoidal components for a waveform and performing modification by altering the parameters of the above equation, namely the amplitudes, phases and frequencies. It has some advantages over models such as TD-PSOLA in is that it allows adjustments in the frequency domain. While frequency domain adjustments are possible in the linear prediction techniques, the sinusoidal techniques facilitate this with far fewer assumptions about the nature of the signal and in particular don t assume a source and all-pole filter model. 

Residual excited linear prediction performs LP analysis, but uses the whole residual in res mthesis rather than an impulse. The residual is modified in a manner very similar to that of PSOLA. 

PSOLA, which operates in the time domain. It separates the original speech into frames pitch-synchronously and performs modification ly overlapping and adding these frames onto a new set of epochs, created to match the synthesis specification. Residual-excited linear prediction performs LP analysis, but uses the whole residual in resynthesis rather than an impulse. The residual is modified in a manner very similar to that of PSOLA. 

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