JPH0447725A - Voice signal multiplexer - Google Patents

Abstract

PURPOSE:To attain multiplexing without the degradation of quality of a voice signal by providing a signaling signal speed conversion means which assigns plural channels in the lump with respect to a specific time slot other than the time slot assigned to the voice signal to the multiplexer. CONSTITUTION:A voice signal multiplexer 21 is provided with a multiplexer circuit 22, for which a 1st speed converter 24 connected to a 1st control memory 23 and a 2nd speed converter 26 connected to a 2nd control memory 25 are connected. The voice signal multiplexer 21 is provided with a demultiplexer circuit 31, for which a 3rd speed converter 33 connected to a 3rd control memory 32 and a 2nd speed converter 35 connected to a 4th control memory 34 are connected. In this case, a specific time slot except a time slot used for the assignment of the voice signal is shared for the assignment of signaling signals by plural channels to apply multiplexing. Thus, signal multiplexing with less deterioration in the voice signal is attained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a digital signal multiplexing device, and in particular to an audio multiplexing device that multiplexes an audio signal encoded by a pulse code modulation method and a control signal. The present invention relates to a signal multiplexing device.

[Conventional technology]

Pulse code modulation (hereinafter referred to as PCM) communication is widely used as a digital signal transmission method. When transmitting, for example, an audio signal using this method, the PCM-encoded audio signal is multiplexed with a control signal (hereinafter referred to as a signaling signal) and then sent out onto a transmission path.

For example, in early PCM-24 type multiplexers, for every time slot, the encoded audio signal 7
Octet multiplexing was used to allocate a total of 8 bits, including bits and 1 bit of a signaling signal.

On the other hand, at present, PCM=24B type multiplexers which are improved from this are often used, and efforts are being made to particularly improve quantization noise level characteristics and transmission loss level characteristics. In this device, signaling signals are multiplexed using a so-called bit steal method. In this pit steal method, one bit for signaling signal transmission is not allocated to every frame, but is transmitted only once every six frames.

FIG. 3 shows the frame structure of the pit-steal system used in the conventional PCM-24B type multiplex system. As shown in Figure (a), this method has a 12-multiframe configuration in which one multiframe is composed of 12 frames. As shown in Figure (b), each frame consists of 24 time slots 13-1 to 13-24 each consisting of 8 bits and a frame bit 14, and each time slot corresponds to a communication path channel. The multiframe bits 14 form a predetermined pattern that rotates every multiframe.

Of these, a 1-bit signaling signal 15 and a 7-bit encoded audio signal 16 are assigned to each time slot in the sixth frame 11 and the twelfth frame 12, as shown in FIG. To each time slot in the other frames, only the 8-bit encoded audio signal 17 is assigned, as shown in FIG. 3(d).

Each frame has a length of 125 μS (microseconds),
Each time slot corresponds to each 64 Kb/S path channel.

[Problem to be solved by the invention]

In this way, in the conventional audio signal multiplexing device, one bit of each time slot of the 6th and 12th frames is used for transmitting the signaling signal, so the signaling signal transmission rate RS is calculated by the following equation (1). become that way.

R, = 2/12 [b/5) Xi/125 [μS]
-1333 [b/s] ...... (1) In other words, the transmission speed of the audio signal is 1333 b/s per channel.
s, and is no longer 64 Kb/s.

Also, since the audio signal is 8-bit encoded in frames other than the 6th and 12th frames, the number of quantization levels is 28, that is, 256 levels, but in the 6th and 12th frames, it is 7-bit encoded. Therefore, the number of quantization levels is 27, that is, 128 levels. For this reason, the encoding quality deteriorates compared to the case of a transmission rate of exactly 64 Kb/s, which has the disadvantage that the quality of the transmitted voice also deteriorates.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an audio signal multiplexing device that can multiplex encoded audio signals without deteriorating their quality.

[Means for Solving the Problems] The present invention provides (i) encoding the encoded audio signals for each communication path channel into predetermined time slots within a frame as a series of signal groups that are repeated at a constant cycle; audio signal speed conversion means for performing speed conversion for allocation;
1) Signaling signals prepared for each communication path channel for transmitting various control information are converted into audio signals using an audio signal rate conversion means among time slots within a multi-frame, which is a set of a predetermined number of consecutive frames. The audio signal multiplexing device is provided with a signaling signal speed conversion means for performing speed conversion for collectively allocating a plurality of channels to a specific time slot other than the time slot allocated for the purpose of the audio signal multiplexing device.

In the present invention, instead of multiplexing the signaling signals by distributing them to each time slot, specific time slots other than the time slots used for allocating audio signals are shared for allocating signaling signals for multiple channels. We will perform multiplexing by using

〔Example〕

The present invention will be described in detail with reference to Examples below.

FIG. 1 shows an audio signal multiplexing apparatus in one embodiment of the present invention. This audio signal multiplexing device 21 is provided with a multiplexing circuit 22, which includes a first speed converter 24 connected to a first control memory 23 and a second speed converter 24 connected to a second control memory 25. A converter 26 is connected thereto. Among these, the first speed converter 24 includes a PC (not shown).
An audio signal 27 encoded by the M encoding section is input, and a signaling signal 28 from a control section (not shown) is manually input to the second speed converter 26. The control memories 23 and 25 each store information specifying the position within the frame of the time slot to which the encoded audio signal 27 and the signaling signal 28 are to be allocated (hereinafter referred to as time slot position specification information). has been done.

The audio signal multiplexing device 21 is also provided with a separation circuit 31, which includes a third speed converter 33 connected to a third control memory 32 and a fourth speed converter 33 connected to a fourth control memory 34. A speed converter 35 is connected. The third of these
The fourth speed converters 33 and 35 output an audio signal 36 and a signaling signal 37, respectively. The control memories 32 and 34 each store information (hereinafter referred to as sampling position designation information) indicating the position at which the separated signal from the separation circuit is to be sampled.

Further, the multiplexing circuit 22 and the separating circuit 31 are connected to transmission lines 38 and 39, respectively.

FIG. 2 shows the frame structure of the multiplexed signal sent from the multiplexing circuit 22 of FIG. 1 onto the transmission line 38. As shown in (a) of this figure, each frame has 12
It consists of a time slot TS having a length of 5 μS and showing a multi-frame pattern, and time slots T S + to TSh each consisting of 8 bits. Time slots TSI to TSn are each 6
It has a 4 Kb/s band and corresponds to one channel of a PCM encoded audio signal. Here, it is assumed that one multiframe is composed of m frames, as shown in FIG.

The operation of the audio signal multiplexing device configured as above will be explained.

When an audio signal 27 of 64 Kb/S is inputted to the speed converter 24 from an audio signal output section (not shown), this signal is transmitted to the speed converter 24 in a time slot designated by time slot position designation information stored in advance in the control memory 23. It is converted and input to the multiplexing circuit 22.

Similarly, the signaling signal 28 input to the speed converter 26 is speed-converted into m time slots specified by the time slot position designation information of the control memory 25 within one multiframe, and the multiplexing circuit 22 is input.

The multiplexing circuit 22 multiplexes the audio signal and the signaling signal and sends the multiplexed signal onto the transmission line 38.

Here, assuming that a time slot TSh is set in advance for the signaling signal, each bit of the signaling signal is divided into time slots TS, , I to TS within the multi-frame, as shown in FIG. 2(b). , , , are speed-converted to be assigned to bits bll to bff18. In this case, all the audio signals 27 are encoded with 8 bits, and the time slots )TS, ~TS
,,+ are assigned.

For example, if the number m of multiframes is 8 and the transmission rate of the signaling signal is IKb/S, then the time slot TS can transmit signaling signals for 64 channels. At this time, the transmission speed of the audio signal remains exactly 64 Kb/s, and no speed reduction occurs due to the transmission of the signaling signal.

On the other hand, the multiplexed signal taken in from the transmission line 39 to the separation circuit 31 is separated in a completely reverse procedure to that for multiplexing, and speed conversion is performed by speed converters 33 and 35. That is, by sampling the audio signal from the time slot designated by the sampling position designation information stored in the control memory 32, the speed of the audio signal is converted to a 64 Kb/s audio signal for each channel, and the signaling signal is , the speed is converted for each channel by sampling time slots based on the sampling position designation information in the control memory 34.

In this embodiment, it is assumed that a predetermined time slot is set in advance for the signaling signal, but it may be set arbitrarily. This makes it possible to flexibly handle the case where, for example, the band of the signaling signal used differs for each channel.

〔Effect of the invention〕

As explained above, according to the present invention, instead of distributing signaling signals to each time slot and multiplexing them, a specific time slot other than the time slot used for allocating audio signals is used for multiple channels. Since we decided to share and multiplex the signaling signals, the audio signals of all frames are processed using the same number of bits.
M encoding is possible. Therefore, compared to the conventional method in which the number of quantization bits has to be reduced in some frames due to the insertion of signaling signals, it is possible to perform signal multiplexing with less deterioration of audio signals.

Furthermore, by making it possible to arbitrarily set the position within a multiframe of a time slot that is shared for signaling signal assignment, it is possible to flexibly handle cases where signaling signals of different bands are used for each channel.

[Brief explanation of the drawing]

1 and 2 are for explaining one embodiment of the present invention, of which FIG. 1 is a block diagram showing an audio signal multiplexing device, and FIG. 2 is a block diagram showing an audio signal multiplexing device of FIG. 1. FIG. 3 is an explanatory diagram showing a frame structure of a multiplexed signal multiplexed by a conventional audio signal multiplexing device. 21...Audio signal multiplexing device, 22...
・Multiplexing circuit, 23.25.32.34... Control memory, 24
．． 26.33.35... Speed converter, 27.3
6...Audio signal, 28.37...Signaling signal, 31...
... Separation circuit. Applicant NEC Corporation Agent
Patent attorney Umeo Yamauchi 1 and 9

Claims (1)

[Claims] An audio signal speed that performs speed conversion to allocate encoded audio signals for each channel to predetermined time slots within a frame as a series of signal groups that are repeated at a constant cycle. converting means, and converting the signaling signal prepared for each of the communication path channels for transmitting various control information into the audio signal rate converter among the time slots in the multi-frame as a set of a predetermined number of consecutive frames. and signaling signal speed conversion means for performing speed conversion for collectively allocating a plurality of channels to a specific time slot other than the time slot allocated for the audio signal by the means. conversion device.