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From text to speech: The MITalk system
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y(nT)=A"x(nT)+B 'x(nT-T )+C’x(nT-2T) @)
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where x (nT-T) and x(nT-2T) are the previous two samples of the input x(nT), the
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constants A”, B’ and C” are defined by the equations:
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A’=1/A
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B’=-B/A ©)
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C'=—C/A
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where A, B, and C are obtained by inserting the antiresonance center frequency F
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and bandwidth BW into Equation 2.
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12.1.8 Low-pass resonator
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As a special case, the frequency F of a digital resonator can be set to zero, produc-
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ing, in effect, a low-pass filter which has a nominal attenuation skirt of -12 dB per
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octave of frequency increase and a 3-dB down break frequency equal to BW/2.
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The voicing source contains a digital resonator RGP used as a low-pass filter that
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transforms a glottal impulse into a pulse having a waveform and spectrum similar
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to normal voicing. A second digital resonator, RGS, is used to low-pass filter the
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normal voicing waveform to produce the quasi-sinusoidal glottal waveform seen
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during the closure interval for an intervocalic voiced plosive.
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12.1.9 Synthesizer block diagram
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A block diagram of the synthesizer is shown in Figure 12-6. There are 39 control
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parameters that determine the characteristics of the output. The name and range of
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values for each parameter are given in Table 12-1. As seen from the table, as
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many as 22 of the 39 parameters are varied to achieve optimum matches to an ar-
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bitrary English utterance. The constant parameters in Table 12-1 have been given
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values appropriate for a particular male voice, and would have to be adjusted
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slightly to approximate the speech of other male or female talkers. The list of vari-
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able control parameters is long, compared with some synthesizers, but the em-
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phasis here is on defining strategies for the synthesis of high-quality speech. We
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are not concerned with searching for compromises that would minimize the infor-
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mation content in the control parameter specification.
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12.1.10 Sources of sound
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There are two kinds of sound sources that may be activated during speech produc-
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tion (Stevens and Klatt, 1974). One involves quasi-periodic vibrations of some
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structure, usually the vocal folds. Vibration of the vocal folds is called voicing.
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(Other structures such as the lips, tongue tip, or uvula may be caused to vibrate in
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sound types of some languages, but not in English.)
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The second kind of sound source involves the generation of turbulence noise
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