JP3179641B2 - Loop type audio conference circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a voice addition method in a case where a plurality of terminals are connected in a loop to conduct a multipoint voice conference.

[0002]

2. Description of the Related Art There is known a technology of connecting a plurality of voice terminals (telephones) via a communication network to hold a voice conference. In particular, Japanese Patent Laid-Open Publication No. Heisei 3 discloses a technology in which a terminal uses two communication paths (channels) and connects each communication path to a different ground to form a ring transmission loop as a whole and perform a voice conference. -289850 (method and apparatus for establishing a conference connection). In the above-mentioned known example, a plurality of terminals for performing a telephone conference are incorporated as ring nodes in a network, and each node has a voice drop / insertion function.
Is performed. More specifically, the voice received by the terminal in the past is subtracted from the received voice from the loop, and this is used as the received voice of the own terminal, and the new voice of the own terminal is added and transmitted to the loop. A so-called N-1 addition method using signals is described.

[0003]

In the technique described above, a signal which has been encoded with high efficiency for band compression is used as a transmission / reception signal for a loop transmission line. For example, a pulse code modulated (PCM) μ-Law code or adaptive differential pulse code modulation (ADPCM) is used. Since such codes cannot be directly added or subtracted, they must be converted to linear codes and then subjected to an addition / subtraction operation (N-1 addition). At this time, mixing of so-called quantization noise cannot be avoided. This quantization noise is generated at each node in the loop and goes around the loop. However, since the loop itself constitutes a complete integrator in signal processing, a phenomenon occurs in the loop where noise power increases and communication quality deteriorates. SUMMARY OF THE INVENTION It is an object of the present invention to provide a voice conference circuit capable of maintaining good conference call quality by removing the above-mentioned loop noise.

[0004]

In the case where N-1 addition of voice is to be performed via a loop transmission path, quantization noise is further reduced on the transmission path because the transmission path is encoded and decoded. It cannot be increased. In the present invention, as shown in the principle configuration diagram in FIG. 1, it is good that the quantization noise generated in the transmission path coding goes around the loop once or more than twice. It was configured to prevent That is, it is connected to a loop-type transmission line, adds its own transmission input signal to the reception input signal from the transmission line to generate a transmission output signal to the transmission line, and outputs its own reception signal from the transmission line. A configuration of a four-terminal audio conferencing network for removing a transmission input signal and providing a reception output signal. Means for giving a reception attenuation signal by adding
A means for adding a signal input from a transmission input terminal to the reception attenuation signal and subtracting an erasure signal generated by the local simulating means to generate a transmission signal, and compressing the transmission signal to obtain a transmission output code. A transmission path encoding means for extracting quantization noise, which is a difference from the transmission signal included in the transmission output code, in the transmission path encoding means as an input to the local simulating means together with the transmission input signal; ,
As such local simulating means, the transmission status of a signal circulating along a loop-type transmission path is equivalently represented by loop delay, loop loss, and repeated transmission path coding and decoding. It is configured in such a manner.

[0005]

As shown in FIG. 1, the quantization noise component generated by the transmission path coding means is fed back to the local simulating means. The local simulating means includes a delay element and a loss element representing the transmission status per round of the transmission loop.
Furthermore, it is equivalently expressed by elements such as transmission path encoding / decoding means. Therefore, the extracted quantization noise component together with the transmission input signal reaches the adding / subtracting means as an erasure signal through a process similar to one round of the transmission path, so that only the signal generated by the own terminal is erased by the own terminal with responsibility. Can do things. Thus, the signal (including noise) does not return to the loop, thereby significantly improving the signal to noise ratio or speech quality.

[0006]

Embodiments of the present invention will be described below in detail with reference to the drawings. First, FIG. 4 illustrates a situation where the audio conference circuit according to the present invention is connected in a loop through a transmission line. The N conference circuits (1 to N) are ring-connected via communication paths (CHi, CHj), and transmit and receive a reception input signal Rin (t) and a transmission output signal Sout (t). Further, the transmission input signal Sin (t) and the reception output signal Rout (t) are input / output outside the ring.

Next, the principle configuration of the audio conference circuit of the present invention will be described with reference to FIG. The voice received from the communication path is given to the reception input terminal 30. Since this is a high-efficiency coded compression code, it is expanded into a received signal in the form of a linear code by the transmission path decoding means 300, and further attenuated by the loop loss coding means 500. Signal attenuation is essentially necessary to eliminate transmission errors in the loop naturally. Addition / subtraction means 70 is applied to the attenuated signal.
By means of 0, a transmission input signal from the transmission input terminal 10 and an erasure signal from the local simulating means 600 are added or subtracted to create a transmission signal. The transmission signal is transmitted to the transmission path coding unit 400.
The transmission output code is transmitted from the transmission output terminal 40 to the transmission line. Here, coding noise (quantization noise) is applied to the transmission signal by the transmission path coding means.
Is added. The noise is extracted and input to the local simulating means 600 together with the transmission input signal. The local simulating means is capable of accurately performing loop loop transmission from the transmission output 40 to the reception input 30 of the present circuit by means of loop delay, loop attenuation, and repeated coding and decoding. This is an important feature of the present invention.

According to the present invention, the transmission input signal input to the audio conferencing circuit and the quantization noise forced to be injected are accurately canceled by the cancellation signal, ending with only one loop circulation. The prevention of this recirculation contributes to the improvement of speech quality (signal-to-noise ratio, noise during no speech, and echo reduction). The reception output signal can be obtained at the reception output terminal 20 by, for example, tapping the transmission signal and subtracting the input signal.

FIG. 2 shows an example in which the principle of FIG. 1 is more specifically implemented. In this example, the loss to be provided during the loop is uniformly distributed to each conference circuit. For example, A = -1db
Assign values before and after. In the entire loop, N-
NAdb is attenuated. The transmission line decoding circuit 300, loop loss encoding circuit 500, addition / subtraction circuit 700, loop simulation circuit 600, and transmission line decoding circuit 400 shown in FIG. 2 all correspond to those in FIG. are doing. Further, a part of the other terminal conference circuit is abbreviated as the whole loop. Further, symbol C in FIG. 2 is an 8-bit μ-law encoding circuit, D is an 8-bit μ-law decoding circuit, and T is a rule.
.Alpha. Represents a multiplication coefficient of .alpha. <1.0 for giving a loss, in which the delay amount of the entire loop is intensively expressed. (A = 20 Log (α) with respect to A described above.) A signal reaching the reception input terminal 30 is equivalently α-attenuated, encoded, and decoded only once before being output to the transmission output terminal 40. Therefore, the local simulate circuit repeats this process N times and is constituted by the continuous connection of the concentrated delay T.

Next, the loss to be inserted into the loop is concentrated on only one terminal conference circuit (this loss is hereinafter referred to as L = α).
FIG. 3 shows a specific configuration example in a case where no loss is allocated to the other N-1 conference circuits (α = 1.0). The symbol numbers assigned to the circuits are the same as those in FIGS. The loss L is given to the loss concentration terminal as the loop loss, and α = 1.0 is given to other terminals. The loss appearance in the loop around the loop excluding itself is α = 1.0 when viewed from the loss concentration terminal, and always L when viewed from the other terminals, so the loss expression in the local simulate circuit is described above. Is reversed. In addition, encoding and decoding at the same signal level produce the same result even when repeated a plurality of times (repeat of the same code word and the same representative value).
Therefore, the encoding and decoding are repeated only once to form the entire simulation.

In the specific examples shown in FIGS. 2 and 3, a case where an 8-bit μ-law codec is used as the transmission path coding is shown. However, an adaptive differential pulse code modulation (ADPCM) codec may be used. In this case, the extraction of the quantization noise generated in the transmission path coding circuit may be performed by using the difference between the input signal of the ADPCM codec and the output of the local decoder. As described above, the quantization noise in the transmission line coding unit is extracted and added to the local simulation circuit, and the local simulation circuit expresses the transmission state of the loop around equivalently and accurately. With the present invention, the signal to noise power ratio,
The electrical performance such as noise during non-communication can be improved by 2 to 4 db.

The above-described signal processing can be easily realized by a digital signal processor (DSP), which has been remarkably developed in recent years. Digital communication network (ISD) using DSP
FIG. 5 shows the hardware configuration of the audio conference terminal connected to N). As shown in the figure, the DSP is connected to a voice input / output system (microphone, speaker) and a PCM codec.
It is connected to an SDN transmission line via an ISDN interface circuit. A ROM for storing programs and a RAM for storing data are connected to the outside, and the entire apparatus is controlled by a higher-order microprocessor MPU. As described above, the conference terminal device is easily configured using the DSP.

[0013]

As described above, according to the loop type voice conference circuit of the present invention, the quantization noise generated in the transmission path coding unit is extracted to simulate the transmission around the loop. Since a means for creating an erasure signal by adding this to the local simulate circuit is provided, loopback of the quantization noise can be prevented, and good speech quality can be ensured. Quantitatively describing an example of the improvement of speech quality, when N = 5 points are connected in a loop and a μ-law codec (8 bits) is used as a transmission path coding means, how to insert a loop loss and An effect of about 2 to 5 db can be obtained although it depends on the number of measurement points from the signal insertion point. When a 7-bit ADPCM codec is used as the transmission path coding means, the signal-to-noise ratio (S / N) can be improved by 3 to 4 db. Of course, the noise during no call is 3-5.
db is improved. Further, the improvement in S / N also contributes to the improvement of the ability to cancel the reception output of the own transmission signal to itself, and the effect of the present invention is great.

[Brief description of the drawings]

FIG. 1 is a diagram showing the principle configuration of the present invention.

FIG. 2 is a circuit diagram of a conference circuit device of the present invention (loss: distributed to each terminal).

FIG. 3 is another circuit configuration diagram (loss: concentrated on one terminal) of the conference circuit device of the present invention.

FIG. 4 is a configuration diagram of a loop type audio conference circuit in which the conference circuit devices of the present invention are connected in a ring shape.

FIG. 5 is a diagram showing an example of a specific hardware configuration of the conference circuit device of the present invention.

[Explanation of symbols]

1, 2, ..., N: audio conference circuit, 10: transmission input terminal, 20: reception output terminal, 30: reception input terminal, 40: reception input terminal ..., Transmission output terminals, 300, 400, a circuit for mutually converting between a linear code and a high-efficiency code, 700,..., An addition / subtraction circuit, 500,. ...... Local simulation circuit.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Daiichiro Takashima 216 Totsuka-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Inside the Hitachi, Ltd. Information and Communications Division (72) Inventor Hiroyuki Matsui 1-1-1, Uchisaiwaicho, Chiyoda-ku, Tokyo No. 6 Inside the Telegraph and Telephone Corporation (72) Inventor Yasuhiro Tomita 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Japan Within (72) Inventor Tsutomu Irishima 1-1-1 Uchisaiwaicho, Chiyoda-ku, Tokyo No. 6 Inside the Telegraph and Telephone Corporation (56) References JP-A-3-289850 (JP, A) JP-A-5-129989 (JP, A) JP-A-2-148926 (JP, A) (58) Field surveyed (Int.Cl. ⁷ , DB name) H04M 3/42-3/58 H04B 14/00-14/08 H04B 1/76-3/60 H04B 7/005-7/015

Claims (1)

(57) [Claims] 1. A plurality of sounds connected in a loop on a transmission line.
A voice conference circuit that performs conference communication between voice conference circuits.
To decode the input code received from the transmission path
Decoding means for obtaining a force signal;
Processing to reduce the loss that occurs when going around the loop
Loop loss processing means for reducing the loop loss
Enter the received input signal in your own audio conference circuit.
The added transmission input signal and the self
A station that simulates the transmission input signal of a live audio conference circuit
Subtracts the erasure signal created by the
Adding / subtracting means for obtaining a transmission signal by encoding the transmission signal
To obtain a transmission output code and transmit it to the transmission path, and
Amount that is the difference from the above transmission signal included in the transmission output code
Encoding means for extracting sub-sampling noise;
The transmission input signal and the quantization noise
Input from the above transmission signal to your own audio conference circuit.
Audio conferencing by subtracting the transmitted input signal
Output as a reception output signal from the circuit.
Loop type audio conference circuit.