SU1751853A1 - Adaptive speech codec - Google Patents

Abstract

The invention relates to computing and telecommunications. Its use in digital low-speed telephone channels allows the codec to be simplified by eliminating an additional communication channel. This is achieved by cutting off signals commensurate with noises on the transmitting side and specifically performing a speech envelope selector on the receiving side. Codec, in addition to communication channel 9; contains on the transmitting side 1 threshold element 10, shaper threshold level 11, compressor 2, clock generator 3, delta modulator 4, on receiving side 5 - delta demodulator 6, expander 8 and speech envelope selector 7, including delay element 18, an adder modulo two 12, a counting trigger 13, 2 integrators 14 and 15, an analog adder 16 and a low-pass filter 17. 10-2-4-9-18-12-13-14-16-17-8.11 -2, 3-4, 9-6-8, 9-12, 13-15-16. 2 ill., 1 tab. xftL y Ј 4 SP 00 (L SA) Figure 1

Description

The invention relates to telecommunications and can be used in various communication systems to create digital low-speed telephone communication channels.

Delta-modulated communications devices are known that convert an analog signal to a digital one.

However, the known devices provide a low signal-to-noise ratio at the output of the demodulator, they do not have the stability margin of the pause combination.

The closest to the present invention is a device containing on the transmitting side a serially connected compressor and a delta modulator, as well as a clock frequency generator, the first output of which is connected to the auxiliary input of the delta modulator, the second and third outputs are connected to respectively connected delta a speech signal envelope modulator and a key, and on the receiving side a serially connected delta modulator and expander, as well as a delta demodulator of the signal envelope, the output of which is dklyuchen to the control input of the expander.

However, the known device is complex in its technical essence, it contains two delta modulators on its receiving and transmitting sides, and to transmit information about the envelope of the speech signal, an additional communication channel is required as part of the multi-channel communication path, which makes it impossible application of this device in single-channel communication systems.

The purpose of the invention is to simplify the codec by eliminating an additional communication channel.

The goal is achieved in that a delta-modulation communication device containing a compressor and a clock generator on the transmitting side, the outputs of which are connected respectively to the information and clock inputs of the delta modulator, and on the receiving side a delta demodulator and envelope selector. speech signal, the outputs of which are connected respectively to the information and control inputs of the expander, the output of which is the output of the codec, the output of the transmitting-side delta modulator is connected through the communication channel to the input mi delta demodulator and the speech envelope selector of the receiving side, additionally TG, on the transmit side, the threshold element and the threshold level generator, the output of which is connected to the control input of the threshold element,

the input of which is the input of the codec, the output of the threshold element is connected to the input of the compressor, on the receiving side the speech envelope is selected

on a modulo-two adder, a counting trigger, integrators, an analog adder, a low-pass filter, and a delay element whose input is combined with the first input of the modulo-two adder and is

0 input selector envelope of the speech signal, the output of the delay element connected to the second input of the modulo two adder, the output of which is connected to the input of the counting trigger, direct and inverse outputs

5 of which through the first and second integrators are connected to the inputs of an analog adder, the output of which is connected through a low-pass filter to the output of the speech envelope selector.

0 FIG. 1 shows a structural electrical circuit of the device; in fig. 2 - time diagrams.

The adaptive speech codec contains on the transmitting side 1 compressor 2 and a similar generator 3, the outputs of which are connected respectively to the information and clock inputs of the delta modulator 4, on the receiving side 5 - the Delta-demodulator 6 and the speech envelope selector 7, the outputs which are connected respectively to the information and control inputs of the expander 8, the output of which is the output of the codec. Output of the transmitting side delta modulator via channel 9

The communication link 5 is connected to the inputs of the delta demodulator and the speech envelope selector of the receiving side. The device contains additionally entered on the transmitting side of the threshold element 10

0 and a threshold level generator 11, the output of which is connected to the control input of the threshold element, whose information input is the input of the codec. Threshold output connected

5 to the compressor inlet. On the receiving side, the speech signal envelope 7 is made on the adder 12 modulo two, the counting trigger 13, the integrators 14 and 15. the analog adder 16, the low pass filter 17 and the delay element 18, the input of which is combined with the first input of the adder module two and is the input to the speech envelope selector. The output of the delay element is connected to the second input of the modulo two adder, the output of which is connected to the input of the counting trigger, the direct and inverse outputs of which through the first and second integrators are connected to the inputs of the analog adder, the output of which through the lower filter

Frequency connected to the output of the envelope of the speech signal envelope

FIG. 2 The following notation is accepted: a - speech signal at the input of the codec; b - signal at the output of compressor 2; в - signal at the generator output 3 clock pulses; g - signal at the output of the transmitting side 1; d - signal at the output of the delta-demodulator 6; e is the signal at the output of the adder 12 modulo two; W is the signal at the direct output of the counting trigger 13; h - signal at the inverse output of the counting trigger 13; and - the signal at the output of the analog adder 16; K - speech signal at the output of the codec.

The speech codec works as follows.

The speech signal x (t) in the 0.3-3.4 kHz band (Fig. 2a) is fed to the input of the threshold element 10, which resects all signals that have an amplitude below Unop, which is generated by the threshold level generator 11 and is selected experimentally in depending on the level of acoustic noise in which the codec operates. The use of the threshold element 10 allows one to eliminate the parasitic quantization of acoustic noise by the delta modulator 4, thereby significantly improving speech quality and forming a stable pause combination. From the output of the threshold element 10, the speech signal enters the input of the compressor 2, is clipped (Fig. 26), and the output of the latter is fed to the input of the delta modulator 4, where it is quantized at a frequency of FT (Fig. 2c). The output delta stream Z (t) (Fig. 2d) is fed through the communication channel 9 to the receiving side 5, where it goes to the delta demodulator 6 and the speech envelope selector 7. In the delta demodulator 6, the signal of the delta stream Z (t) is converted into the signal x (m) (Fig. 2e), the dynamic range of the latter being much smaller than that of the original speech signal x (t). The dynamic range is expanded in expander 8, the expansion coefficient of which is determined by the control signal from the output of the speech envelope selector 7.

The delta stream Z (t), which is fed to the input of the selector 7 of the speech signal envelope, is fed to the first input of the modulo two 12 adder, to the second input of which the same signal is fed, but with a delay of one clock cycle. Modulo two adder 12 separates the edges of the pulses from the input delta flow, corresponding to the transition of the speech signal through zero (Fig. 2e), which are fed to the input of the counting trigger 13, on the forward and inverse output of which positive Q is formed (Fig. 2g) and negative Q (Fig. 2h) of the information signal sequence, the duration of which 5 depends on the signal level x (t) at the input of the codec. The resulting Q and Q sequences are integrated with RC integrators 14.15 with a constant time of 8–10 s, combined in analog

0 is an adder 16 (Fig. 2i) and is fed to the low-pass filter 17, at the output of which the signal controlling the expander 8 is formed. At the output of the expander 8, the recovered speech signal x (t) is obtained (Fig. 2k).

5 Since in the proposed codec, only transitions of the speech signal through zero are subject to quantization, the conversion rate is chosen from the relation, where FB is the highest frequency in the spectrum of the converted speech signal. Thus, the proposed codec is designed to operate at speeds from 6.8 kbit / s to 12-16 kbit / s. At higher conversion rates, existing

5 adaptive delta codecs provide the best quality parameters.

Example. The effectiveness of the proposed codec was evaluated by conducting comparative articulation tests in conjunction with the prototype and the delta modulator currently used in commercially available communications equipment. The evaluation was conducted at a speed of 16 kbit / s; 9.6 kbps; 8 kbps; 4.8 kbps

5 The research results are presented in the table.

The tests carried out showed the feasibility of using the proposed codec in digital systems.

0 telephone communication with data rates of 8-12 kbps. The use of the proposed speech codec makes it possible to reduce the speed of speech conversion by a factor of 1.5-1.8, eliminating the need for an additional communication channel to transmit information about the envelope of a speech signal at a speech quality comparable to the quality of existing delta codecs. Compared to parametric speech conversion devices (vocoders) operating in the same speed range, the proposed codec has significantly smaller dimensions, mass, power consumption and cost.

five

Claims (1)

Claims of the invention An adaptive speech codec containing a compressor and a clock generator on the transmitting side, the outputs of which are connected respectively to the information and clock inputs of the delta modulator, on the receiving side there is a delta demodulator and a speech envelope selector, the outputs of which are connected respectively to the information signal and to the control inputs of the expander, the output of which is the output of the codec, the output of the delta-modulator of the transmitting side is connected to the inputs of the delta-demodulator and the allocator via a communication channel envelope of the receiving side speech signal, characterized in that, in order to simplify the codec by avoiding additional communication channel at the transmitting side and a threshold element introduced shaper threshold level, the output of which is connected to the control input of the threshold element whose data input is input the codec, the output of the threshold element is connected to the input of the compressor; at the receiving side, the speech signal envelope selector is made on the adder on the module two, a counting trigger, integrators, an analog adder, a low-pass filter and a delay element whose input is combined with the first input of a modulo-two adder and is an input of a speech envelope selector, the output of the delay element is connected to the second input of a modulo-two. the output of which is connected to the input of the counting trigger, the direct and inverse outputs of which through The first and second integrators are connected to the inputs of an analog adder, the output of which is connected via a low-pass filter to the output of a speech envelope selector. ) The frequency band of the speech signal is limited to 0.3-2.4 kHz. / s g & /// AEZ EZ UU //// L t J22 YS / L // L AND Z2 about I II II I I I I I I I III III I I I I I I I I I 2 (t) I til II MM T GTT III I F 1 V7X Ч777Х WS / Л W77 V7 У /// Л 0 ffl V Ч77Л У /// Л Z2 til II MM M I 111 I I W //// L i