JPH05143099A - Speech encoding and decoding device - Google Patents

Abstract

PURPOSE:To prevent a pitch error from being generated by employing long- period prediction for the encoding of pitch synchronism by a speech synthesizer. CONSTITUTION:This speech encoding and decoding device is provided with an A/D conversion part 1 which obtains a digital speech signal from an analog signal, a synthesized waveform storage part 2 stored with a synthesized waveform obtained by decoding a last code, an acoustic analysis part 3 which finds a long-period prediction coefficient and a basic waveform of one pitch by taking a pitch analysis and a long-period predictive analysis of the digital speech signal, and a speech synthesis part 5 which generates the synthesized speech according to the codes of the acoustic analysis part 3 and basic waveform encoding part 4 and stores it in the synthesized waveform storage part 2. Then the device is provided with a basic waveform decoding part 7 which decodes the basic waveform of one pitch, a speech waveform decoding part 7 which decodes the digital speech signal, and an A/D conversion part 8 which converts the digital speech signal outputted by the speech waveform decoding part 7 into the analog speech signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voice coder / decoder used for a voice codec for digital mobile communication and a voice synthesizer for voice output of various devices.

[0002]

In the field of digital mobile communications,
In order to cope with the increase in the number of subscribers, there is a demand for a lower bit rate speech coding method, and research and development are being carried out at each research institute. And now the bit rate is 8 kb
ps is standardized, and each research institute has 4.8 kbps
We are conducting research and development towards low bit rates.
However, a voice encoding / decoding device having sufficient performance has not yet been obtained.

The technique for realizing a low bit rate is described in the following 2
It can be divided into street ways. First, the first method is a method in which a speech in a certain analysis section is encoded by an LPC system parameter and a driving sound source and a pitch component is generated by a long-term prediction filter, as represented by CELP. This method is currently the most efficient method for medium bit rates of 6.7kbps to 16kbps.
However, at 4 kbps or less, the sound quality is considerably deteriorated, and it is difficult to realize a low bit rate.

The second method is a method in which most of human voice is voiced sound having a fundamental frequency, and pitch analysis is performed to transmit only pitch and one pitch waveform. This method is quite effective for encoding at 6 kbps or less, and can be said to be the most effective method for realizing a low bit rate. However, an error always occurs in pitch detection.
Also, the amount of calculation required for pitch detection is quite large, and it can be said that pitch detection in real time is difficult.

Therefore, it has been considered difficult to realize a low bit rate for the above reasons.

[0006]

As described above, it has been difficult to realize a low bit rate with the conventional voice encoding / decoding technology. This is because long-term prediction does not provide sufficient sound quality, and pitch synchronization makes it difficult to detect pitch.

In view of the above problems, the present invention realizes a low bit rate by combining the advantages of the two methods and by using long-term prediction for pitch synchronization encoding to prevent pitch errors. With the goal.

[0008]

In order to achieve this object, a first invention of the present invention provides an A / D converter for obtaining a digital voice signal from an analog voice signal, and an A / D converter for decoding a previous code. A synthesized waveform storage section that stores synthesized waveforms, an acoustic analysis section that performs a pitch analysis and a long-term prediction analysis on a digital speech signal in a certain section to obtain a long-term prediction coefficient and a basic pitch of 1 pitch, and an acoustic A basic waveform encoding unit that encodes a one-pitch basic waveform obtained by the analysis unit, and a synthetic sound is created based on the codes obtained by the acoustic analysis unit and the basic waveform encoding unit and stored in the synthetic waveform storage unit. And a voice synthesizer.

A second aspect of the present invention is a basic waveform decoding section for decoding a 1-pitch basic waveform, a speech waveform decoding section for decoding a digital speech signal in a certain section,
And a D / A conversion unit for converting the digital audio signal output from the audio waveform decoding unit into an analog audio signal.

[0010]

With the above-described structure of the present invention, a low bit rate can be realized by encoding a one-pitch basic waveform, and pitch error can be prevented because long-term prediction is used. Therefore, low bit rate speech coding can be performed efficiently.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, 1 is an A / D conversion section, 2 is a synthesized waveform storage section, 3 is an acoustic analysis section, 4 is a basic waveform coding section, 5 is a speech synthesis section, 6 is a basic waveform decoding section, 7 is a speech waveform decoding unit, 8 is a D / A conversion unit, 10 is an encoder, 11
Is a decoder.

Next, the operation of the speech encoding / decoding apparatus according to the first embodiment of the present invention will be described.

First, the function of the encoder 10 will be described with reference to FIG. The A / D converter 1 converts an input voice input from a microphone (not shown) into a digital signal. Next, in the acoustic analysis unit 3, a voice signal of a fixed time is taken into a RAM memory (not shown), and the correlation between this analysis section and the synthetic waveform stored in the synthetic waveform storage unit 2 is analyzed.
The pitch analysis of the analysis section is performed at the same time, and the position of the partial section of the correlated waveform and the basic waveform of one pitch are obtained. For this parameter and the method of extracting the basic waveform,
A detailed description will be given later.

Further, in the basic waveform encoding unit 4,
The basic waveform obtained in the acoustic analysis unit 3 is encoded.
Specific methods include a method of matching the phases and performing VQ as a waveform, a method of converting into a frequency domain and then encoding.

Here, in the speech synthesizing section 5, the basic waveform of one pitch is decoded based on the code obtained in the basic waveform coding section 4, and the long-term prediction coefficient extracted in the acoustic analysis section 3 and the above-mentioned basic waveform. Decrypt using and
The obtained composite waveform is stored in the composite waveform storage unit 2. The function of the speech synthesis unit 5 is a combination of the functions of the basic waveform decoding unit 6 and the speech waveform decoding unit 7 in the decoder 11, and the details thereof will be described when the decoder 11 is described.

Here, the method of extracting the parameters and the basic waveform in the acoustic analysis unit 3 will be described in detail. The synthesis formula of the present invention is shown in (Equation 1).

[0018]

[Equation 1]

In this (Equation 1), n is the pitch section number,
q is a pitch period, β is a long-term prediction coefficient, p is a long-term prediction pitch, Xnq + i and Xnq + ip are all synthetic waveforms, and Yi is a decoded basic pitch of one pitch.

Therefore, p, q, β and Yi are calculated so that the waveform synthesized by this synthesis formula is closest to the original waveform.

Now, given p and q, the original waveform

[0022]

[Equation 2]

The error power between the composite waveform of and (Formula 1) is as shown in (Formula 3) below.

[0024]

[Equation 3]

Here, E is the error power, and M is the number of pitch periods in one analysis section. Therefore, it is used that when E is the minimum, the values differentiated by β and Yi are both 0. First, when differentiated by β, (Equation 4) is obtained.

[0026]

[Equation 4]

Therefore, by using the following (Equation 5) and (Equation 6) to simplify the equation and solve for β, (Equation 7) is obtained.

[0028]

[Equation 5]

[0029]

[Equation 6]

[0030]

[Equation 7]

On the other hand, when (Equation 3) is differentiated by Yk, (Equation 8) is obtained.

[0032]

[Equation 8]

Then, by substituting (Equation 8) into (Equation 7), β
And each value is used to find each Yk. This is performed for all p and q, the error E is evaluated, and p and q with the smallest error are selected.

However, a full search for these p and q requires a large amount of calculation. As a method of reducing the calculation amount, there are a method of narrowing down and searching candidates of p and q by the value of Vp, a method of setting q to the value of p at the maximum Vp, and the like.

Next, the function of the decoder 11 will be described with reference to FIG. First, in the basic waveform decoding unit 6, 1
Synthesizes the pitch basic waveform. Then, the speech waveform decoding unit 7 uses the 1-pitch basic waveform synthesized by the basic waveform decoding unit 6 and the long-term prediction coefficient to generate a speech waveform of one analysis section based on the synthesis formula (Equation 1). To synthesize.
Then, the D / A converter 8 converts the analog signal and outputs the analog signal.

In order to verify the coding effect of the speech coding / decoding apparatus of the present invention, a preliminary simulation experiment of speech coding / decoding was conducted. The voice for evaluation is "the explosion sound spreads to the plateau of the silver world" uttered by one man, and is encoded with a sampling rate of 8 kHz and 12 bit-PCM. In the simulation, the basic waveform coding
It was used as it was without decoding or scalar coding of β. Both p and q were coded with 7 bits. As a result, a segmental S / N ratio of 13.75 dB was obtained,
There was no pitch error. In addition, 1 pitch waveform is 14
Considering that the coding can be performed with ˜20 dB, the coding can be performed with the S / N ratio of 9 to 12 dB. Therefore, it is possible to achieve the above object.

[0037]

As described above, according to the present invention, the pitch error is prevented from occurring by using the long-term prediction for the pitch synchronization encoding. Therefore, the voice is encoded at the low bit rate without causing the pitch error. And can be decrypted.

[Brief description of drawings]

FIG. 1 is a block connection diagram of a voice encoding / decoding device according to an embodiment of the present invention.

[Explanation of symbols]

 1 A / D conversion unit 2 Synthetic waveform storage unit 3 Acoustic analysis unit 4 Basic waveform coding unit 5 Speech synthesis unit 6 Basic waveform decoding unit 7 Speech waveform decoding unit 8 D / A conversion unit 9 Transmission path 10 Encoder 11 Decoder

Claims (2)

[Claims] 1. An A / D conversion unit for obtaining a digital voice signal from an analog voice signal, a synthesized waveform storage unit for storing a synthesized waveform obtained by decoding a previous code, and a digital voice signal for a certain section. On the other hand, an acoustic analysis unit for performing a pitch analysis and a long-term prediction analysis to obtain a long-term prediction coefficient and a 1-pitch basic waveform, and a basic waveform encoding unit for encoding the 1-pitch basic waveform obtained by the acoustic analysis unit. A speech coder comprising: a sound synthesizing section; and a speech synthesizing section for generating a synthesized sound based on a code obtained by the basic waveform coding section and storing the synthesized sound in the synthesized waveform storage section. 2. A basic waveform decoding unit for decoding a one-pitch basic waveform, a voice waveform decoding unit for decoding a digital voice signal in a certain section, and a digital voice signal output from the voice waveform decoding unit. A voice decoding device having a D / A conversion unit for converting the signal into an analog voice signal.