JP3332616B2 - Audio decoder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an audio decoder.
In particular, MPEG (Moving Picture Expert Group)
) It relates to an audio decoder.

[0002]

2. Description of the Related Art In recent years, the use and development of MPEG, which is an international standard for data compression indispensable for practical use of multimedia, has been promoted. In MPEG, along with the standardization of MPEG video, which is a compression / decompression method for video information,
MPEG audio, which is a compression / expansion method of audio information, is also being standardized.

[0003] Acoustic signals can be classified into audio signals having a bandwidth of about 3.1 kHz, quasi-audio signals having a bandwidth of about 7 kHz, and audio signals having a bandwidth of 15 to 20 kHz. A quasi-audio signal of about 7 kHz is used for telephone, mobile communication, teleconference, and the like. As typical examples of the data compression method, LD-CELP having an encoding bit rate of 16 kbps and 8 kbps of 8 kbps used in mobile communication. VSELP and the like. Also, 15
Techniques have been developed for compressing the bandwidth of audio signals with a compression rate of 1/6 to 1/8 for wideband audio signals of up to 20 kHz without deteriorating the audible quality by utilizing human auditory characteristics. MD (Mini Disk) and DCC (Digital Com
pact Caset) and MPEG audio.

[0004] The compression system used in MD and DCC is a system adopted only in audio equipment. On the other hand, since MPEG audio is a general-purpose standard, it can be used in communication, broadcast, storage, and computer media, or in an environment in which the media are integrated. And M
By combining PEG audio and MPEG video, a multimedia system can be easily constructed.

A human auditory characteristic (acoustic psychological model) used in MPEG audio has a masking effect and a minimum audible characteristic. The masking effect means that when a loud sound is generated at a certain frequency, sounds below a certain level at frequencies near the loud sound become inaudible or difficult to hear. Also, the minimum audible characteristic is the number of human ears.
It is most sensitive to the 100Hz human voice band, and has a certain frequency characteristic that sounds below a certain level cannot be heard in the ultra-low range or the ultra-high range. Therefore, the masking effect and the minimum audible characteristic are combined to set a mask level that dynamically changes together with the audio (music) signal, and the signal below this level is data-compressed. IE
C11172-3) In layer 1, the encoding bit rate; 192k, 128kbps, compression ratio: 1/4, sound quality is CD-DA
(CD Digital Audio) and PCM (Pulse Code Modul)
ation), the coding rate at layer 2 is 128k, 96k
bps, compression rate: 1/6 to 1/8, sound quality is equivalent to MD and DCC, and compression effect and sound quality such as coding rate in layer 3, 128k, 96, 64kbps, compression rate: 1/6 to 1/12 Is obtained.

In an MPEG audio encoder, first, an input audio signal is divided into 32 sub-bands using a band division filter. Next, in the quantization, by using the masking effect and the minimum audibility characteristic as described above and by not assigning bits to the masked sound that cannot be heard, the information amount is reduced and data compression is performed.

FIG. 2 shows a main block circuit of an MPEG audio decoder "LC8230" developed by the present applicant. "LC8230" is a decoder LSI compliant with the MPEG1 audio standard layers 1 and 2.
It receives the compressed code data and outputs a PCM signal that can be decompressed and passed directly to an audio D / A converter. As a result, CD karaoke and CD-IFMV (CD-I
Full Motion Video) and can be applied to multimedia PCs.

The MPEG audio decoder 1 comprises an inverse quantization section 2, a band synthesis section 3, an output section 4, a RAM 5, and the like. Code data (input data) read from a recording medium (not shown) such as a video CD is MPEG.
Is input to the inverse quantization unit 2 via a system bus (not shown). In the inverse quantization unit 2, inverse quantization of quantization in the encoder is performed. In the band synthesizing unit 3, a product-sum operation is performed by a butterfly operation using the RAM 5, and data divided into 32 sub-bands by the encoder is 1.
Are combined into one. The data is output as a PCM signal (digital audio output) via an output unit 4 including an output interface unit and a cross attenuator conforming to the CD-I standard. The digital audio output is D / A converted by a D / A converter (not shown),
An analog audio signal is obtained.

[0009]

In the MPEG audio decoder 1, the recording medium is defective (such as a scratch on a video CD).
If erroneous input data is input due to, for example, noise may occur in the digital audio output. Since the noise is also D / A converted by the D / A converter together with the digital audio output, noise is also generated in the analog audio signal. As a result, there is a problem that the user feels harsh or the speaker is damaged due to excessive input.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide an audio decoder which does not generate noise even if erroneous input data is input.

[0011]

[Means for Solving the Problems]

[0012]

According to a first aspect of the present invention, there is provided a dequantizer for dequantizing input data, a band synthesizer for synthesizing input data divided into subbands by performing a product-sum operation, and a band synthesizer. The gist of the invention is to provide a mute means for detecting a product-sum operation value in the section and muting the output when the value exceeds a certain value.

According to a second aspect of the present invention, there is provided an inverse quantizer for inversely quantizing input data, a band synthesizer for synthesizing input data divided into subbands by performing a product-sum operation, and a band synthesizer. The gist of the invention is to provide a mute means for detecting a product-sum operation value in the unit and, when the value exceeds a predetermined value, muting the output for a predetermined time.

According to a third aspect of the present invention, there is provided a dequantizing unit for dequantizing input data, a band synthesizing unit for synthesizing input data divided into subbands by performing a product-sum operation, and a synthesizing unit. An output unit that outputs the input data as a PCM signal to the outside and a product-sum operation value in the band synthesis unit are detected, and when the value exceeds a certain value, the output unit is controlled to mute the output. And a mute means for applying

According to a fourth aspect of the present invention, there is provided a dequantizing unit for dequantizing input data, a band synthesizing unit for synthesizing input data divided into subbands by performing a product-sum operation, and a synthesizing unit. An output unit that outputs the input data as a PCM signal to the outside, and a product-sum operation value in the band synthesis unit is detected. If the value exceeds a certain value, the output unit is controlled to keep the output constant. The gist of the present invention is to provide a mute means for muting for a time.

[0017]

[Action]

[0018]

According to the invention as set forth in any one of claims 1 to 4 , the product-sum operation value in the band synthesis section is detected by the mute means, and when the value exceeds a certain value, the output is output. Mute is applied. In the product-sum operation in the band synthesizing unit, it is determined that the product-sum operation value does not exceed a certain value when a correct input is made in accordance with the MPEG audio standard. Conversely, if an erroneous input that does not conform to the MPEG audio standard is made, the product-sum operation value exceeds a certain value (the product-sum operation value overflows). Accordingly, by muting the output when the product-sum operation value exceeds a certain value, generation of noise can be prevented.

Furthermore, according to the invention described in claim 2 or claim 4 , since the time during which such an erroneous input is made is very short in most cases, the mute is released after a certain time. In this case, a normal output can be obtained continuously.

According to the third or fourth aspect of the present invention, the provision of the output unit enables more reliable output delivery.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIG. In this embodiment, the same components as those in the conventional example are denoted by the same reference numerals.

MPEG audio decoder 1 of the present embodiment
1 is an inverse quantization unit 2, a band synthesis unit 3, an output unit 4, and a RAM
5, an error detection circuit 12 and the like. Code data (input data) read from a recording medium such as a video CD is input to the inverse quantization unit 2 via an MPEG system bus. In the inverse quantization unit 2, inverse quantization of quantization in the encoder is performed. In the band combining unit 3, a product-sum operation is performed by a butterfly operation using the RAM 5, and data divided into 32 sub-bands is combined into one by the encoder. The data is output as a PCM signal (digital audio output) via an output unit 4 including an output interface unit and a cross attenuator conforming to the CD-I standard. The digital audio output is supplied to a D / A converter (not shown).
/ A conversion to obtain an analog audio signal.

Here, the product-sum operation in the band synthesizing unit 3 is determined so that the product-sum operation value does not exceed a certain value when correct input data conforming to the MPEG audio standard is input. . Conversely, when erroneous input data that does not conform to the MPEG audio standard is input, the product-sum operation value exceeds a certain value (the product-sum operation value overflows). Therefore, the error detection circuit 12 detects the product-sum operation value in the band synthesizing unit 3, and when the value exceeds a certain value, judges that erroneous input data has been input and controls the output unit 4. By doing so, the digital audio output is muted for a certain time.
More specifically, the output terminal 4 is muted by short-circuiting the output terminal for a predetermined time.

Therefore, according to the present embodiment, when erroneous input data is input due to a defective recording medium (such as a scratched video CD), the digital audio output is muted for a certain period of time. It is possible to prevent noise from occurring in the audio output. Since the time when such erroneous input data occurs is very short in most cases, if the mute is released after a certain time, a normal digital audio output can be obtained continuously. Note that the time for muting the digital audio output may be determined by a specific experiment using various defective recording media.

By the way, the above embodiment may be modified as follows. Even in such a case, the same operation and effect as the above embodiment can be obtained. (1) The output terminal of the output unit 4 is not short-circuited for a fixed time, but is controlled by controlling a cross attenuator in the output unit 4 to mute. In this case,
The level of the digital audio output may be reduced to a level at which noise does not become harsh and does not damage the speaker.

(2) Instead of controlling the output unit 4, the output terminal of the band synthesizing unit 3 is short-circuited for a predetermined time to mute. (3) Instead of muting the digital audio output for a certain period of time, the digital audio output is completely stopped when erroneous input data is input.

(4) When incorrect input data is input, a display means (a warning lamp, a visual display using a display, etc.) for notifying the user of the input data is provided. Although the embodiments have been described above, technical ideas other than the claims that can be grasped from the embodiments will be described below together with their effects.

(A) The audio decoder according to any one of claims 1 to 4 , wherein the band synthesizing unit performs a product-sum operation by a butterfly operation using a RAM.

In this way, the product-sum operation in the band synthesis unit can be performed accurately. (B) The audio decoder according to any one of claims 1 to 4 , further comprising display means for notifying a user of an erroneous input when the erroneous input is made.

In this manner, the user can know that an erroneous input has been made. By the way, in this specification, MPEG means not only MPEG1 audio standard layers 1 and 2, but also MPEG1 audio standard layer 3, MPEG2 audio standard, and MPEG4 audio standard.

[0032]

As described in detail above, according to the present invention, an audio system which does not generate noise even if erroneous input data is input.
An audio decoder can be provided.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram of one embodiment.

FIG. 2 is a block circuit diagram of a conventional example.

[Explanation of symbols]

 2 Inverse quantization unit 3 Band synthesis unit 4 Output unit 5 RAM 12 Error detection circuit as mute means

Claims (4)

(57) [Claims] 1. An inverse quantization unit for inversely quantizing input data, a band synthesis unit for combining input data divided into sub-bands by performing a product-sum operation, and a product-sum operation value in the band synthesis unit And a mute means for muting the output when the value exceeds a certain value. 2. An inverse quantization unit for inversely quantizing input data, a band synthesis unit for synthesizing input data divided into subbands by performing a product-sum operation, and a product-sum operation value in the band synthesis unit And a mute means for muting the output for a certain time when the value exceeds a certain value. 3. A dequantizer for dequantizing input data, a band synthesizer for synthesizing input data divided into sub-bands by performing a product-sum operation, and a PCM for synthesizing the synthesized input data. An output unit that outputs the signal as an external signal; and a mute unit that detects the product-sum operation value in the band synthesis unit and, when the value exceeds a certain value, controls the output unit to mute the output. Equipped audio decoder. 4. A dequantizer for dequantizing input data, a band synthesizer for synthesizing input data divided into sub-bands by performing a product-sum operation, and a PCM for synthesizing the synthesized input data. Mute that detects the product-sum operation value in the output unit that outputs it as a signal to the outside and the sum of products in the band synthesis unit, and when the value exceeds a certain value, controls the output unit to mute the output for a certain period of time. Audio decoder comprising means.