JP2000354066A - Method for transmitting digital audio signal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for transmitting digital audio signals by which synchronization can be reestablished, without inverting the phases of right and left channels nor increasing redundancy, even when out of synchronization exist on a transmission line. SOLUTION: At sending of digital audio signals D compressed by means of transmitting-side equipment 1, in a method for transmitting digital audio signal, the signals D are sent out by rewriting the header data A for synchronization of one channel (for example, R-ch) of the head data A (the same fixed data for right and left channels) added to the head of each sound frame (the basic unit of compressed transmission data for right and left channels) of the signals D, to the header data B for synchronization which is fixed data differing from the data A. On the receiving side, it is discriminated that synchronization has been restored to normal, when the different header data A and B are alternately detected before and after receiving one sound frame, and the synchronization is re-established without making phase inversion, even when the synchronization is broken due to data disappearance on a transmission line by performing a series of procedures of resending the signals D to a decoder by rewriting the header data B of one channel (R-ch) to the original header data A.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a general public telephone network or ISDN (Integrated Services Digital Network).
The present invention relates to a digital audio signal transmission technique for transmitting a time-divided digital audio signal such as music software using a network and a transmission path such as a PHS or a mobile phone.

[0002]

2. Description of the Related Art Hi-fi analog audio signals such as records and analog tapes are A / D converted and transmitted in the form of digital data, or hi-fi digital audio signals such as CD music software are transmitted through transmission lines (general public networks such as telephone lines). ), A recent data compression technique, such as MP3 (moving picture image coding)
xperts group 3; MPEG1 layer 3), REAL
AUDIO, TWIN VQ, AAC, ATRAC
(Adaptive Transform Acoustic Coding) by applying various data compression technologies,
/ 18 to 1/20, and a transfer speed of about 100 Kbps, making it possible to transmit digital audio signals almost in real time.

That is, the transmission speed of a CD (compact disk), which is a typical recording medium of digital audio signals in current music software, is based on a sampling frequency (4
4.1 KHz) × the number of quantization bits (16 bits) × the number of channels (2 ch) = 1.4112 Mbps. However, a digital audio signal (music software) such as a CD can be used as it is on an existing telephone line (data transmission speed is generally 33.6K over an analog transmission line network (PSTN line)).
bps (bits per second), 64Kb over ISDN line
ps. ), The transmission time becomes very long. Therefore, recently, the amount of music software data is often compressed and transmitted by the compression technique.

By the way, M shown in the system diagram of FIG.
Also in a D or CD reproducing apparatus (mechanical & storage medium), when music data is reproduced from a package medium, data of left and right channels (hereinafter also referred to as L-ch and R-ch) are alternately extracted, and a system is constructed. In the digital data format inside, the right channel data and the left channel data are transferred in a time-division manner. At this time, another signal for channel synchronization (channel synchronization signal) can be separately extracted from the medium or can be identified by redundant data, so that synchronization establishment is always compensated and there is no problem.

On the other hand, in the transmission of a two-channel digital audio signal via a general public network such as a telephone line, the same digital data is processed. However, in the transmission and reception of a two-channel digital audio signal via a transmission path, a channel synchronization signal for returning to the other party once the channel synchronization is lost cannot be obtained. Required. Hereinafter, a transmission method of a current 2-channel digital audio signal through a general public network will be outlined.

FIG. 4A shows an example of a compression format.
4 (b) shows the transmission rate conversion, and FIG. 4 (c) shows the channel data format to be transmitted.

In general, the compression of a digital audio signal is performed by compressing a fixed number (for example, 1024) of sample data as shown in FIG.
The compressed data after compression is output from the encoder in a burst manner (referred to as a burst signal). Hereinafter, the basic unit (m Byte) of the compressed music data is referred to as a sound frame.

The burst signal is converted to a signal having a constant transfer rate when it is transmitted to the transmission line as shown in FIG. Generally, transmission data on this transmission path often includes various types of redundant data other than audio signal data. However, from the viewpoint of transmission efficiency, redundant data is reduced as much as possible to increase transmission efficiency. Of course, it is desirable.

[0009] The decoder of the recording device on the receiving side checks the synchronization header data of the first byte of each of the time-divided left and right channel sound frames of FIG. Perform decoding processing. As the synchronization header data, a fixed data pattern (referred to as header data A) common to the L-ch header and the R-ch header which does not generally appear in the music data is selected.

When an error occurs in a transmission path between data transmission and reception and a plurality of bytes of data are lost,
The sound is cut off once the sound frame is out of sync.

However, immediately, the reproducing device on the receiving side detects the header data A of the fixed data pattern and establishes synchronization again, and the sound is transmitted again to the decoder.

The following is a brief description of a conventional synchronization recovery procedure for transmitting and receiving a digital audio signal via a general public transmission network such as the telephone line.

FIG. 6 is a flowchart showing a conventional control procedure of a signal processing unit for synchronization recovery.

The control CPU on the receiving side stops (a) data transmission to the decoder until synchronization is established again when synchronization is lost and an error is detected. Upon detection, when the header data A is detected, (c) one sound frame data is received, and (d) thereafter, it is determined whether or not the header data A of the next sound frame is detected again.
(E) When it is detected, it is determined that it has returned to normal,
(F) Generally, a procedure of re-synchronization is established and output to the decoder is restarted.

[0015]

However, in the above-mentioned conventional transmission system, as described above, the resynchronization confirmation procedure for detecting whether or not the header data A is detected before and after receiving one sound frame data is performed on the transmission path. It is possible to recover from the trouble.
Since the signals of ch and L-ch are sent alternately, the left and right channels may be reversed after the recovery only by the above procedure (called phase inversion). In addition, the header data A is the same in the R-ch and L-ch sound frames and is not distinguished.

Of course, another signal (channel synchronization signal) for achieving channel synchronization similar to that of the above-described reproducing apparatus may be separately added as redundant information of the audio signal. However, the transmission speed of the compressed data and the transmission line is at least equal. Therefore, when the redundancy of the audio signal is increased, the continuous transmission time is reduced as it is, and it is desirable to avoid increasing the redundancy.

According to the present invention, when a compressed digital audio signal is transmitted to a general public transmission network, part of the data is rewritten and transmitted without increasing the redundancy, and even if a data error occurs on the transmission path, The present invention also provides a method for re-establishing synchronous reception of the left and right channels on the receiving side without phase inversion based on the rewritten information.

[0018]

According to the present invention, as shown in FIG. 3, a digital audio signal D which has been time-divided into two channels (R-ch and L-ch) is transmitted from the transmitting device 1 to the receiving device 2. This is a method of transmitting the digital audio signal D to the general public transmission line 3 through the line control device 5 as shown in FIG. Of one of the left and right channels of the synchronization header data A (eg, R-
ch), the header data A for synchronization is rewritten to the header data B for synchronization of fixed data different from the other, and the data is transmitted. The receiving-side apparatus 2 of FIG. 3 transmits the data of the general public transmission path 3 as shown in the flow of FIG. When some data is lost in the process and synchronization is lost, (a) data transmission to the decoder 6 is temporarily stopped, and the synchronization header data A and B for the left and right channels are changed to one sound frame data reception. (B), (c) and (d)}, (e) by rewriting one of the rewritten synchronization header data B to the original state and sending it to the decoder 6 (f). The above-mentioned problem of establishing resynchronization without phase inversion by a digital audio signal transmission method characterized by comprising a series of resynchronization procedures for establishing resynchronization Accomplish.

[0019]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram illustrating an operation of rewriting header data in the digital audio signal transmission method according to the present invention, and FIG. 2 is a flowchart illustrating a synchronization recovery procedure according to the present invention. It should be noted that the transmission method of the present invention is intended for general public transmission lines, for example, a public telephone line network, an IS
For example, a DN telephone network, a mobile telephone or a PHS wireless telephone network.
FIG. 3 is a diagram illustrating establishment of synchronization of the transmission system according to the present invention.

As shown in FIG. 3, in the method of transmitting a two-channel digital audio signal of the present invention, two
The time-division digital audio signal D of the channel (L-ch, R-ch) is transmitted from the transmitting device 1 to the receiving device 2.
This is a method of transmitting the digital audio signal D to the general public transmission line through the line control device 5 on the transmission side, as shown in FIG. One of the left and right channel synchronization header data A indicating the delimitation of the sound frame (for example, R-c in FIG. 1).
h) is rewritten to the synchronization header data B of fixed data different from the other and transmitted, and the receiving side transmits the general header data as shown in the flow chart for explaining the synchronization recovery procedure shown in FIG. When some data is lost in the transmission process of the public transmission path 3 and synchronization is lost, (a)
When the data transmission to the decoder 6 is temporarily stopped, and the synchronization header data A and B having different left and right channels are detected before and after reception of one sound frame data from (b) to (c) and (d), respectively. (E) replacing the rewritten one of the synchronization header data B with the original header data A;
Is rewritten, and sent to the decoder 6 to obtain (f)
A series of synchronization recovery procedures for establishing re-synchronization are provided.

That is, the gist of the present invention resides in that the transmission side apparatus 1 sets the L-ch, L-ch at the beginning of each sound frame in the digital transmission form of the digital audio signal D time-divided.
By rewriting the header data A of the same fixed data in the R-ch and rewriting only the header data of the sound frame of one of the channels to a different header data B (A ≠ B), and transmitting the rewritten data, the receiving side without increasing the redundancy. The apparatus 2 can identify the L-ch and R-ch sound frames in the time-divided digital audio signal D, and receive different header data A and header data B alternately before and after one sound frame. In other words, by detecting whether or not the L-ch sound frame having the header data A is correctly received, it is possible to determine whether or not the synchronization has been restored without inverting the phase. Note that the procedure for rewriting the header data A to B at the transmitting device 1 and the procedure for rewriting the header data B to the original header data A at the receiving device 2 and establishing resynchronization are as follows. This is realized by the transmission-side apparatus 1 and the reception-side apparatus 2 incorporating in a control program of a transmission protocol programmed in both control microcomputers in advance.

[0023]

According to the digital audio signal transmission method according to the present invention, in the transmission of a digital audio signal of two channels via a general public network such as a telephone line, a data error on a transmission line without increasing redundancy is achieved. Occurs, the synchronous reception of the left and right channels can be re-established on the receiving side without phase inversion.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an operation of rewriting header data in a digital audio signal transmission method according to the present invention.

FIG. 2 is a flowchart illustrating a synchronization recovery procedure according to the present invention.

FIG. 3 is a diagram for explaining synchronization establishment of the transmission system according to the present invention.

4A is a diagram of a compression format example, FIG. 4B is a diagram of transmission speed conversion, and FIG. 4C is a diagram of a channel data format to be transmitted.

FIG. 5 is a simple system diagram of a reproducing apparatus (mechanical & storage medium).

FIG. 6 is a flowchart showing a conventional control procedure of a signal processing unit for synchronization recovery.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transmission side apparatus 2 Receiving side apparatus 3 General public transmission line 5 Line controller 6 Decoder A Header data B Header data different from A D Digital audio signal data

Claims (1)

[Claims] 1. A method of transmitting a time-division digital audio signal of two channels, left and right, from a transmitting apparatus to a receiving apparatus via a general public transmission path, wherein the transmitting side transmits the digital audio signal to the general public transmission. When transmitting the digital audio signal through the line control device, the synchronization header data of one channel in the synchronization header data of the left and right channels indicating the sound frame delimiter of the digital audio signal is converted into the synchronization header data of fixed data different from the other. When the data is lost and part of the data is lost in the transmission process of the general public transmission line and the synchronization is lost, the reception side temporarily stops data transmission to the decoder, and the synchronization header data of the left and right channels different from each other. Is detected before and after the reception of one sound frame data. A digital audio signal transmission method comprising a series of synchronization recovery procedures of rewriting one of the changed synchronization header data to return to the original state and sending the data to a decoder.