JPH06349198A - Audio decoding circuit and method - Google Patents

Abstract

PURPOSE:To enable performing a control which is not included in a header by utilizing an auxiliary data. CONSTITUTION:In a device decoding an audio code string 6 constituted of a header including a synchronous bit, a CRC check word, audio code bits and auxiliary data, an auxiliary data read-out part 4 stores an nth auxiliary data 9 in a storage circuit 5. An (n+1)th frame is controlled by making the output of the storage circuit 5 to be a control data 12. Further, the output of a 1st frame is processed with a muting since an auxiliary data corresponding to a 1st audio data is not present.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for decoding coded audio data. In particular, it relates to an LSI for decoding MPEG audio signals.

[0002]

2. Description of the Related Art Utilizing human auditory characteristics, a wide band (20KHH
z) A coding technique for compressing an audio signal to about 1/6 to 1/10 is being actively developed. One of such encoding methods is the international standard MPEG (11172-3) standard in ISO / IEC.

The audio format of the MPEG standard has a structure in which a header (32 bits) including a bit for synchronization, a CRC check word when performing a CRC check, an audio code bit encoded subsequently, and an auxiliary data at the end. Has become. The contents of this 32-bit header are shown below.・ Synchronization bit (12 bits) ・ ID bit (1 bit, indicates MPEG) ・ Layer bit (2 bits, indicates layer) ・ Protection bit (1 bit, indicates whether CRC check is performed) ・Bit rate information (4 bits) ・ Sampling frequency (2 bits) ・ Padding bit (1 bit, addition of remainder word at 44.1 KHz) ・ Private bit (1 bit) ・ Mode bit (2 bits, stereo, monaural, etc.・ Extended mode bit (2 bits, used in joint stereo mode) ・ Copyright (1 bit) ・ Original / copy (1 bit) ・ Emphasis (2 bits) Header information and auxiliary data are 1 frame (Layer 1) 384 samples, and layer 2 1152 samples).

The auxiliary data is user-defined in the MPEG audio standard. Also, US LS
MPEG audio decoding LSI "Product number L"
64111 ”, the auxiliary data is sent to the LSI via FIFO memory.
It is designed so that an external CPU or controller can read it.

[0005]

The advantage of header information is that
It is a point adjacent to audio data. For example, when the "emphasis" included in the header information indicates "present", the emphasis information can be latched and the restored PCM data in the frame following the header can be subjected to the emphasis processing. In this case, there is no need for an external host CPU to intervene, and processing with no control delay is possible.

However, with the header information described in the preceding paragraph, it is not possible to perform all the control of the decoding processing and the processing on the PCM data of the decoding processing result. The control information not included in the header information includes, for example, control of the attenuation amount of the sound pressure level at the output stage. In the MPEG standard,
CRC check is included in the standard. However, the CRC check can detect a bit error, but it does not correct the error. When using a mode that does not perform error correction or using communication in a storage medium such as a CD-ROM, a CRC check that only detects bit errors may be insufficient. In some cases, not only error detection but also error correction is necessary.

The above-mentioned control is performed by the external CP for each frame.
What U does is difficult to control due to synchronization issues with the audio output. In order to solve such a problem, in the present invention, control information such as sound pressure level attenuation and error correction words are added to the auxiliary data area. However, when the auxiliary data is used for such a purpose, there is a problem that the auxiliary data is located at the end of the encoded audio stream after the header information and the audio code bit. The control information included in the restored auxiliary data cannot be used to control the audio data of the same frame.

Further, if the nth auxiliary data is used for controlling the n + 1th audio frame, the control of this nth audio frame becomes a problem. The present invention
Control for the nth frame is also proposed.

[0009]

In the present invention, the auxiliary data of the nth audio frame is stored, and the n + 1th or subsequent audio frame is controlled based on this auxiliary data information. Further, in the present invention, the sound pressure level of the output PCM data is attenuated based on the stored auxiliary data information.

Further, in the present invention, the stored auxiliary data information is an error correction code (ECC), and based on this,
Correct the error. Further, in the present invention, the stored auxiliary data information is the parameter and the filter coefficient of the digital filter for the output PCM data, and the characteristic is changed accordingly.

Further, in the present invention, the PCM output corresponding to the first audio frame is muted.

[0012]

According to the present invention, the auxiliary data included in the audio frame can be used to control each frame. At this time, the control can be performed without including the processing delay.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 is a diagram showing the basic internal structure of a decoding LSI, and FIG. 2 is a diagram showing an audio frame format. Figure 1
In, (6) is a sign bit string signal. The code bit string signal (6) is an audio code string in which a header including a header including sync bits, a CRC check word, audio code bits, and auxiliary data are arranged in this order.

(1) is a synchronization detection / frame analysis unit.
This synchronization detection / frame analysis unit (1)
From (6), perform synchronization detection and frame analysis. (7) is
This is the output of the separated audio code data. (9)
Is the extracted auxiliary data. (2) is a decoding processing unit. The decoding processing unit (2) decodes the audio code bit separated by the frame analysis unit and outputs (8).

(3) is an output controller. This output control unit outputs PCM data (10). (4) is an auxiliary data extracting unit for extracting auxiliary data. (5) is a memory circuit for storing auxiliary data. (11) is an output of the auxiliary data extraction unit (4). (12) is an output (control information) of the memory circuit (5).

In FIG. 2, (13) is the nth audio frame. (14) is the (n + 1) th audio frame. (15) is the audio data of the n-th audio frame (13). (16) is auxiliary data of the n-th audio frame (13). (17) is the header of the (n + 1) th audio frame (13).

(17) is the (n + 1) th audio frame (13)
Audio data. The above operation will be described. Code bit string consisting of header including sync bit, CRC check word, audio code bit, and auxiliary data (6)
Is input to the synchronization detection / frame analysis unit (1).

The audio code bit output (7) from the synchronization detection / frame analysis unit (1) is sent to the decoding processing unit (2).
The audio code bit, in the decoding processing unit (2),
Inverse quantization processing and band synthesis processing are performed, and the output (8)
Is output as a PCM output (10) via the output control unit (3).

The decoding processing unit (2) has an error correction circuit built therein. Further, the output control section (3) has a built-in circuit for attenuating the sound pressure level and a digital filter circuit. On the other hand, the auxiliary data extraction unit (4) extracts the auxiliary data (9) from the audio code string passing through the synchronization detection / frame analysis unit (1). Then, the output (11) of the auxiliary data extracting unit (4) is stored in the memory circuit (5).

The storage in the storage circuit (5) is performed for each frame. One frame is 384 samples (input frequency is 44.
It is equivalent to about 8.7 ms at 1 KHz) or 1152 samples (about 26.1 ms at an input frequency of 44.1 KHz). Therefore, the control information (12) in the auxiliary data (9) is updated for each frame,
It is sent to the decoding processing unit (2) or the output control unit (3).

When the control information (12) includes the attenuation amount of the sound pressure level of the output PCM data, the output control unit (3) attenuates the sound pressure level of the PCM data. Control information (12)
Includes a parameter of the filter processing for the output PCM data of the decoding processing result, the filter processing of the PCM data in the output control unit (3) is adjusted.

When the control information (12) includes an error correction code (ECC), error correction is performed in the preceding stage of the decoding processing unit (2), and the data after the error correction is dequantized,
Add band synthesis processing. If an error correction code for the entire audio data is added as auxiliary data, the auxiliary data area will be large and the audio code data area will be relatively small, resulting in a loss of sound quality. The area for performing the operation is limited to an area including important information called a protected area. For a limited area (bit allocation information, scale factor, etc.), the error correction code (ECC) can be reduced.

In this case, since the audio code data area does not become extremely small, the sound quality is not deteriorated. When the control information (12) is the parameter (filter coefficient) of the filter process for the output PCM data as the decoding process result, the information is used for the digital filter process of the output control unit.

The next control by the auxiliary data (control information) stored in the storage circuit (5) is shown in FIG.
Will be explained. The auxiliary data (16) of the nth audio frame (13) is the same as the nth audio frame (1
It cannot be used to process audio data (15) in 3). The nth auxiliary data 16 is used for processing the n + 1th audio data (18) together with the header (17) of the n + 1th audio frame (14).

As described above, if the processing is shifted by one, the processing of the first audio frame becomes a problem. That is, there is no auxiliary data corresponding to the first (first) audio data. Therefore, the output control unit
In (3), the PCM output of the first frame is invalid, and there is no sound (muting).

That is, at the time of reproducing the first frame, the muting control information (12) is stored as the control information (12), and the sound control level of the PCM data is set to 0 in the output control section (3).
Let In practice, no problem occurs even if the output of the first frame is silenced.

As described above, in this embodiment, the auxiliary data included in the audio frame can be used to control each frame without using an external CPU or the like. At this time, the control can be performed without including the processing delay. As described above, in the audio circuit according to the present embodiment, the auxiliary data is used for the control of each audio frame which is difficult to control from the external host CPU or the like due to the problem of synchronization. At the same time, as control contents, output sound pressure level attenuation, error correction, and digital filter processing can be performed for each frame.

[0028]

As described above, in the present invention, the control for each audio frame can be realized by using the auxiliary data.

[Brief description of drawings]

FIG. 1 is a diagram showing a basic configuration of an embodiment of the present invention.

FIG. 2 is a diagram showing an audio frame format.

[Explanation of symbols]

(1) ・ ・ ・ ・ ・ Synchronization detection / frame analysis section, (2) ・ ・ ・ ・ ・ Decoding processing section (error correction means), (3) ・ ・ ・ ・ ・ Output control section (sound pressure level attenuation means, Digital filter means), (4) ... Auxiliary data extraction section, (5) ... Storage circuit.

Claims (7)

[Claims] 1. An audio decoding circuit for decoding an audio code string (13, 14) in which a header including a sync bit, a CRC check word, an audio code bit, and auxiliary data are arranged in this order, in an n-th audio frame (13 ) Auxiliary data (16) is stored in the memory circuit (5) and the next n + 1th audio frame
(14) Alternatively, an audio decoding circuit that uses control information related to the subsequent audio frames. 2. The control information included in the auxiliary data is
2. The audio decoding circuit according to claim 1, wherein the audio decoding circuit is a digital value indicating an attenuation amount of a sound pressure level of output PCM data as a decoding processing result. 3. The control information included in the auxiliary data is
The audio decoding circuit according to claim 1, wherein the audio decoding circuit is an error correction code (ECC). 4. The control information included in the auxiliary data is
2. The audio decoding circuit according to claim 1, wherein the audio decoding circuit is a parameter of a filtering process for the output PCM data of the decoding process result. 5. An audio decoding circuit for storing auxiliary data of an n-th audio frame in a storage circuit (5) and using it as control information for a next n + 1-th audio frame or a subsequent audio frame. , PCM output of the first audio frame data, silence
Audio decoding device for (muting). 6. An audio decoding method for decoding an audio code string (13, 14) in which a header including a synchronization bit, audio code bits, and auxiliary data are arranged in this order, in which an auxiliary data of an n-th audio frame is stored in a storage circuit. (Five)
An audio decoding method in which the control information is stored in the next n + 1-th audio frame or the subsequent audio frames. 7. An audio decoding method for decoding an audio code string (13, 14) in which a header including a sync bit, audio code bits, and auxiliary data are arranged in this order, in which an auxiliary data of an nth audio frame is stored in a storage circuit. (Five)
An audio decoding method in which the PCM output of the first audio frame data is muted, as well as the control information for the next n + 1th audio frame or subsequent audio frames.