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Vocoders

Vocoders. The Channel Vocoder (analyzer) :. The channel vocoder employs a bank of bandpass filters, Each having a bandwidth between 100 HZ and 300 HZ. Typically, 16-20 linear phase FIR filter are used. The output of each filter is rectified and lowpass filtered.

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Vocoders

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  1. Vocoders

  2. The Channel Vocoder (analyzer): • The channel vocoder employs a bank of bandpass filters, • Each having a bandwidth between 100 HZ and 300 HZ. • Typically, 16-20 linear phase FIR filter are used. • The output of each filter is rectified and lowpass filtered. • The bandwidth of the lowpass filter is selected to match the time variations in the characteristics of the vocal tract. • For measurement of the spectral magnitudes, a voicing detector and a pitch estimator are included in the speech analysis.

  3. Encoder Bandpass Filter Rectifier Lowpass Filter A/D Converter Bandpass Filter Rectifier Lowpass Filter A/D Converter To Channel S(n) Voicing detector Pitch detector The Channel Vocoder (analyzer block diagram):

  4. The Channel Vocoder (synthesizer): • At the receiver the signal samples are passed through D/A converters. • The outputs of the D/As are multiplied by the voiced or unvoiced signal sources. • The resulting signal are passed through bandpass filters. • The outputs of the bandpass filters are summed to form the synthesized speech signal.

  5. The Channel Vocoder (synthesizer block diagram): Decoder D/A Converter Bandpass Filter Output speech ∑ D/A Converter Bandpass Filter From Channel Voicing Information Switch Random Noise generator Pitch period Pulse generator

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