JPH0361960B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a speech synthesis device.

Conventionally, as a type of speech synthesis device, digital filters that approximate the transfer characteristics of the vocal tract have been used.
In the case of voiced sound, a periodic sound source waveform (for example, an impulse train) is input, and in the case of unvoiced sound, an irregular sound source waveform (for example, a random number sequence) is input to synthesize speech. At this time, in order to achieve resonance in the vocal tract or the like with a simple circuit configuration, a so-called cyclic digital filter having a signal return path is often used.

However, in general, the word length (the number of bits required to represent the value) of the product of the signal sample value multiplied by the circuit coefficient is longer than the word length of the original signal (more bits are required). Therefore, in order to perform signal feedback, it is necessary to limit the word length of the product to the word length of the original signal. For this purpose, quantization such as truncation or rounding (equivalent to rounding in decimal) is generally performed on the product or the sum of products. Errors in quantization within this feedback path can be regarded as noise signals generated within the feedback path. When the input signal is an irregular signal, the noise signal caused by this quantization is also irregular (that is, there is no correlation between the samples of the noise signal), and the size is negligible, so there is no real harm. However, if the input signal is periodic, In the case of a signal, it is known that correlation begins to occur between samples of a noise signal, and a frequency parasitic oscillation phenomenon determined by circuit coefficients, regardless of the frequency of the input signal, may occur.

Conventional speech synthesis apparatuses using recursive digital filters have the disadvantage that the above-mentioned parasitic oscillations may occur when synthesizing stationary voiced sounds and the like.

An object of the present invention is to provide a speech synthesis device that can reduce the parasitic oscillation by simply adding a few circuits to a conventional speech synthesis device using a recursive digital filter.

The present invention provides a recursive digital filter that approximates the spectral envelope of speech, a means for generating a periodic signal sequence for a voiced sound source, a means for generating an irregular signal sequence for an unvoiced sound source, and a signal of the two sound source waveforms. In a speech synthesizer of the type having a switching circuit that selects one of the strings and leads it to the input of the digital filter, when the switching circuit selects the periodic signal string, the value of the irregular signal string is transferred to the input of the digital filter. a second switching circuit leading to a feedback circuit; and a quantizer in the feedback circuit of the digital filter for rounding or truncating according to the value of the irregular signal sent through the second switching circuit. configured.

According to the present invention, by simply adding a few circuits to a conventional speech synthesizer, rounding and truncation in the feedback path of a recursive digital filter can be irregularly switched to reduce the correlation of error signals. This has the effect of reducing parasitic oscillations when synthesizing voiced sounds. When the sound source is an irregular signal, that is, when it is an unvoiced sound, the selection of quantization is arbitrary, but in general, rounding reduces the power of the error signal.

Next, embodiments of the present invention will be described using the drawings.

The figure is a block diagram showing one embodiment of the present invention. In the figure, 1 is a control circuit, and based on parameters indicating spectrum envelope information, amplitude information, pitch information, voiced/unvoiced information, etc. inputted from an input terminal 7, a periodic signal generation circuit 2, an irregular Control information transmission lines A9, B10, and C1 are provided for the signal generation circuit 3, switching circuit 4, amplitude adjustment circuit 5, and cyclic digital filter 6, respectively.
1, D12, and E13.

The periodic signal generating circuit 2 generates a periodic signal according to the control signal sent from the control circuit 1 and sends it to the switching circuit 4 via the periodic signal transmission line 14.

On the other hand, when the irregular signal generation circuit 3 receives a control signal instructing to start synthesis from the control circuit 1, it generates an irregular signal and sends it to the switching circuit 4 via the irregular signal transmission line 15.

According to the control information sent from the control circuit 1, the switching circuit 4 connects the irregular signal transmission path 15 to the sound source waveform transmission path A17 when there is no voice, and connects the periodic signal transmission path 14 to the sound source waveform transmission path A17 when there is voice. It is connected to the sound source waveform transmission line A17, and the irregular signal transmission line 15 is connected to the quantized information transmission line 16.

The amplitude adjustment circuit 5 adjusts the amplitude of the sound source waveform (periodic signal or irregular signal) sent through the sound source waveform transmission path A17 according to the control signal sent from the control circuit 1, and controls the sound source waveform transmission path B18. The signal is sent to the cyclic digital filter 6 via the cyclic digital filter 6.

The cyclic digital filter 6 filters the sound source waveform sent through the sound source waveform transmission path B18 in accordance with control information sent from the control circuit 1, and outputs the filtered sound source waveform to the output terminal 8. At this time, if it is a voiced sound, the type of quantization (rounding or truncating) in feedback is switched depending on the value of the irregular signal sent via the quantization information transmission line 16.

[Brief explanation of drawings]

The figure is a block diagram showing one embodiment of the present invention. In the figure, 1 is a control circuit, 2 is a periodic signal generation circuit, 3 is an irregular signal generation circuit, 4 is a switching circuit, 5 is an amplitude adjustment circuit, 6 is a cyclic digital filter, 7 is an input terminal, and 8 is an output Each represents a terminal.

Claims (1)

[Claims] 1. A recursive digital filter that simulates a spectral envelope, means for generating a periodic signal train, means for generating an irregular signal train, and a switching circuit that selects one of the two types of signal trains and guides it to the input of the digital filter. a second switching circuit that guides the value of the irregular signal train to a feedback circuit in the digital filter when the switching circuit selects the periodic signal train; A speech synthesis device comprising a quantizer in a feedback circuit of the digital filter for rounding or truncating according to the value of the irregular signal string sent through the switching circuit.