JP3166319B2 - Audio signal transmission method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio signal transmission system suitable for application to a case where an audio signal is converted into digital data and transmitted wirelessly as in a radio telephone system.

[0002]

2. Description of the Related Art Conventionally, when an audio signal is converted into digital data and transmitted wirelessly as in a wireless telephone system, the audio data is compressed and transmitted on the transmitting side and the receiving side is used in order to effectively utilize the transmission band. The audio data compressed in (1) is converted into original audio data by arithmetic processing. By performing such processing, the amount of data to be transmitted is reduced, and it becomes possible to efficiently transmit audio signals of a plurality of systems in a small frequency band.

[0003]

However, if the compression amount of the audio data is large, there is a disadvantage that the signal processing amount increases on both the transmitting side and the receiving side. That is, the amount of arithmetic processing when compression is performed on the transmission side is increased, and the amount of arithmetic processing for restoring the original audio data is increased on the receiving side, resulting in a disadvantage that the configuration of the transmission device becomes complicated. In particular, in the case of a wireless telephone system such as a mobile phone, it is necessary to reduce the size of the terminal device, but it is difficult to incorporate a circuit for performing compression and decompression with a large amount of processing in a small transmission device. There is.

SUMMARY OF THE INVENTION In view of the foregoing, it is an object of the present invention to reduce the load on a transmission processing circuit when transmitting audio data.

[0005]

According to the present invention, as shown in, for example, FIG. 1, the encoder 14 expands the time axis of a digital signal converted into a digital data, and the vicinity of the end of a silent section included in the audio signal. Then, time axis processing for resetting the time offset amount due to the above expansion is performed, and the audio signal subjected to the time axis processing is transmitted by the transmission circuit 16 after performing predetermined transmission processing.

[0006]

Furthermore, in this case, the signal processing capability of the receiving side of the transmission signal is determined, and if the determined signal processing capability is inferior to the signal processing capability of the transmitting side, the audio signal subjected to the time axis processing is transmitted. It is something to do.

[0008]

According to the present invention, since the audio data before the transmission processing is the data expanded on the time axis, when the transmission processing is performed, the data with the reduced rate by the time axis expanded is transmitted. It can be handled as a signal, so that transmission processing can be performed at a lower rate, and the load on the transmission processing circuit system is reduced.

[0009]

An embodiment of the present invention will be described below with reference to the accompanying drawings.

In FIG. 1, reference numeral 10 denotes a transmitter, and reference numeral 20 denotes a receiver. The receiver 20 receives data transmitted from the transmitter 10. First, the configuration of the transmitter 10 will be described. An audio signal picked up by the microphone 11 is supplied to an analog / digital converter 12 and converted into digital audio data. And an analog / digital converter 1
2 stores the digital audio data output from the buffer memory 1
Supply 3 The buffer memory 13 is configured as a first-in first-out (FIFO) memory, and functions as delay means for reading input data after being delayed for a predetermined time.

The digital audio data output from the buffer memory 13 is supplied to an encoder 14.
The encoder 14 expands the time axis if necessary, and encodes the expanded audio data for transmission into predetermined transmission data. In this case, the expansion processing of the time axis in the encoder 14 is performed under the control of the timing control circuit 15, and the expansion processing is performed so as to delay only the tempo without changing the pitch of the voice. Digital audio data output from the analog / digital converter 12 is directly supplied to the timing control circuit 15 without passing through the buffer memory 13, and the state of the audio data is determined to control the decompression process. Here, as the determination of the state of the audio data, a silent section included in the audio data is detected, and a period during which the detected silent section continues is determined.

The process of extending the time axis by the encoder 14 on the basis of the state of the silent section included in the audio data determined by the timing control circuit 15 will be described. The processing from the first section to the beginning of the next silent section is performed as one unit, and expansion processing corresponding to the length of the silent section following this one unit of audio data is performed. That is, assuming that the length of one unit of audio data at this time is T1 and the length of a silent section following this one unit of audio data is T2, the audio data T1 is set to be equal to or less than (T1 + T2). Extend. When this decompression process is performed, the length T
When the silence section 2 ends, the timing of the input data and the output data of the encoder 14 is adjusted to reset the time offset amount due to the expansion of the audio data. Accordingly, the audio data that is output from the encoder 14 after being decompressed has a silent section shorter in length than the original data.

If the next silent section cannot be detected only by detecting the data before being delayed in the buffer memory 13, the next silent section is determined based on the state of the silent section of the audio data supplied in the past. Is estimated or the period during which a silent section continues. That is, for example, the buffer memory 1
3, a delay of about 3 seconds is performed. If a silent section cannot be detected from the data of 3 seconds, the average interval at which the silent section appears in the past voice data is about 5 seconds, and the average time that the silent section lasts is about 5 seconds. When it is one second, the silent section that appears next is estimated from the average interval and the average time, and the extension processing is performed based on the estimated value.

When the decompression process is performed as described above, data relating to the time offset amount is added as sub-code to the decompressed data every predetermined period. Then, the transmission data obtained by expanding the audio data (or the transmission data not subjected to the expansion processing) is
The signal is supplied to the transmission processing circuit 16 and subjected to compression processing according to a compression method determined by the transmission method of the communication device, modulation processing for transmission, and transmission from the antenna 17 connected to the transmission processing circuit 16 to a predetermined channel. Let it be transmitted. Note that the transmission compression processing is performed to increase transmission efficiency by multiplex transmission or the like, and compression processing other than compression on the time axis may be performed.

Next, the configuration of a receiver 20 for receiving a signal wirelessly transmitted from the antenna 17 of the transmitter 10 will be described. The transmission signal received by the antenna 21 of the receiver 20 is supplied to a reception processing circuit 22. Then, the reception processing circuit 22 demodulates the signal modulated for transmission, and restores the transmission data obtained from the demodulated signal from the state compressed for transmission to the original data amount. At this time, the restoration process is performed based on the timing control signal supplied from the timing control circuit 23. Then, the restored transmission data is supplied to a decoder 24 and decoded to produce audio data. The decoded audio data is supplied to a digital / analog converter 25 to be converted into an analog audio signal, and the converted analog audio signal is converted. The signal is reproduced from the speaker 26.

The processing in the receiver 20 is basically the same regardless of whether the data transmitted from the transmitter 10 has undergone the above-described expansion processing on the time axis or not.

Next, the transmission state of the transmission system of this embodiment will be described with reference to the timing chart of FIG.
A of the figure shows an input audio signal waveform picked up by the microphone 11, and this input audio signal has a timing ta to a timing tb.
It is assumed that there is a silent section m1 up to. At this time, the input audio signal is converted by the analog / digital converter 12 into a signal shown in FIG.
B is converted into digital data of a constant sampling frequency. Then, as shown in FIG. 2C, the audio data in the section before the silent section m1 is expanded by the extension processing in the encoder 14, and the start point t of the silent section
It is assumed that a 'is shifted within the original silent section m1. Therefore, the data output from the encoder 14 has been thinned out in the section indicated by hatching in FIG. 2B (section from point ta to point ta ′).

In this embodiment, as described above, the last part ta 'of the expanded audio data is determined by determining the state of the current input audio data or making an estimation based on the state of the past input audio data. The setting is made so as to be before the end timing tb of the original silent section m1. However,
If it is guessed, this condition may rarely be not satisfied.

The data transmitted from the transmitter 10 is a signal having a constant frame frequency specified by the transmission format, as shown in FIG. 2D. In other words, even when the sampling frequency or the like becomes inconsistent due to the expansion processing performed by the encoder 14, the transmission processing circuit 16 processes the transmission data so that the frame frequency of the transmission data is always constant.

On the receiver 20 side, even when the data is expanded and transmitted, as shown in FIG. Accordingly, in the analog audio signal output from the digital / analog converter 25 shown in F of FIG. 2 (that is, the audio reproduced from the speaker 26), the time axis of the audio portion is extended, and the silent section m2 is shifted from the timing ta ′ to the timing tb. Will be shortened by now. Note that Δ, 2Δ, ‥‥ 6 shown in E and F of FIG.
Δ indicates the amount of deviation from the timing of the original audio data (A and B in FIG. 2), and the amount of deviation can be determined on the receiving side by the subcode included in the transmission data.

By performing the processing in this manner, the reproduced sound obtained on the receiver 20 side is slightly expanded, but the silent section always included in the sound of conversation or the like is slightly reduced. , There is almost no inconvenience in listening to the transmitted voice. In particular, in this example, the pitch is not changed at the time of decompression, and only the tempo is changed.

Since the time axis is extended and transmitted in this manner, the transmission rate of the audio data is reduced, and the transmission processing circuit 16 of the transmitter 10 is used for transmission.
As a result, the rate of the transmission data handled in the case of performing the compression processing decreases, and the rate of the transmission data handled in the case of performing the restoration processing in the reception processing circuit 22 of the receiver 20 decreases. Therefore,
At the time of transmission processing in the transmitter 10 and reception processing in the receiver 20, low-rate data is handled, and the amount of arithmetic processing per unit time in the transmission processing circuit 16 and the reception processing circuit 22 is reduced. The configurations of the transmitter 10 and the receiver 20 can be simplified. In this example,
Since no special processing is performed on the receiver 20 side, the configuration can be simplified from this point as well.

If the transmission-side timing control circuit 15 determines that the transmitted voice data is non-conversational data such as music and that there is almost no silent period, the encoder 14 performs the decompression process. The transmission may be performed on the same time axis without performing the above.

Further, in addition to determining whether or not to perform expansion based on the type of transmitted voice, whether or not to perform expansion may be determined based on the reception processing capability of the receiver 20. That is, before transmitting voice data, the transmitter 10 transmits and receives control data and the like, and the receiver 20
Check the reception processing capacity of When it is determined that the reception processing capability (recovery capability in the reception processing circuit) can cope with the transmission of audio data in real time, the transmission is performed without decompression. Further, when it is determined that the reception processing capacity is such that it is difficult to restore the audio data transmitted in real time (that is, it has only the reception processing capacity suitable for the method of this example), May be transmitted after performing the decompression process.

When the silent section is estimated from the past data as described above, the occurrence of the silent section shorter than the estimated time causes the completion of the expanded sound data before the end.
In rare cases, the next audio data may start, but even in this case, the beginning of the next audio data is slightly cut off. Because the content can be determined from before and after the sentence,
Does not cause much inconvenience. However, in the case of a conversation by telephone or the like, since a silent section occurs very frequently, such a situation hardly occurs unless the decompression rate is set too high.

In each of the above-described embodiments, a method for compressing data for transmission is not particularly shown. However, it goes without saying that a compression method used in various transmission systems such as a radio telephone system can be applied. In addition, the present invention is not limited to the above-described embodiment, but may take various other configurations.

[0027]

According to the present invention, the audio data before the transmission processing is the data expanded on the time axis. Therefore, when the transmission processing is performed, the data whose rate is reduced by the time axis expansion is used. Can be treated as a transmission signal, so that the amount of transmission processing per unit time is reduced, and the load on the transmission processing circuit system can be reduced.

[0028]

Further, the signal processing capability of the receiving side of the transmission signal is determined, and if the determined signal processing capability is inferior to the signal processing capability of the transmitting side, the audio signal subjected to the time axis expansion processing is transmitted. As a result, the time axis expansion processing is performed only when necessary, and the appropriate transmission processing is always performed.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a configuration of a transmission system according to an embodiment of the present invention.

FIG. 2 is a timing chart for explaining one embodiment;

[Explanation of symbols]

 Reference Signs List 10 transmitter 13 buffer memory 14 encoder 16 transmission processing circuit 20 receiver 22 reception processing circuit 24 decoder

Claims (3)

(57) [Claims] 1. An audio signal converted into digital data is expanded by a time axis expansion circuit, and time axis processing for resetting a time offset due to the expansion near the end of a silent section included in the audio signal is performed. An audio signal transmission system in which the audio signal subjected to the time axis processing is transmitted after performing a predetermined transmission process. 2. A signal processing capability on a receiving side of a transmission signal is determined. If the determined signal processing capability is inferior to a signal processing capability on a transmitting side, the time-axis-processed audio signal is transmitted. The audio signal transmission system according to claim 1, wherein 3. The decompression circuit according to claim 1 , further comprising a timing control circuit.
And a processing circuit for actually performing the decompression process, wherein the timing control circuit includes
The processing circuit detects the presence or absence of a silent section and the duration of the silent section, and the processing circuit converts the audio signal according to the detection result.
2. The audio signal transmission according to claim 1, wherein the audio signal is extended.
method.