JP3300205B2 - Coded signal reproduction device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an encoded signal reproducing apparatus for reproducing sound to be heard through headphones, and more particularly to an encoded signal reproducing apparatus for suppressing sound leakage from headphones.

[0002]

2. Description of the Related Art In recent years, in encoding an audio signal or an image signal, an input signal is divided into a plurality of band signals and assigned to each band signal in order to reduce the amount of information to be transmitted or stored while maintaining signal quality. 2. Description of the Related Art High-efficiency coding of band signals is performed by changing the number of quantization bits and the like.

[0003] Encoding by band division is performed, for example, as follows when an audio signal is targeted. At the time of encoding, the original signal is divided into a plurality of (for example, 512) band signals by DCT (Discrete Cosine Transform), the divided band signals are collected into a plurality of groups (for example, 52 groups), and level information for each group is collected. Find the scale factor shown. Next, normalization and quantization of each band signal are performed based on the scale factor of each group and the number of quantization bits assigned to each group, and the scale factor and the number of allocated bits are assigned to the quantized band signal.
An encoded signal is generated by adding other encoded information.
At the time of reproduction, the opposite process to that at the time of encoding is performed on the encoded signal, and the original signal is reproduced.

[0004] When a reproduced signal is listened to by headphones, sound leakage to the outside may cause discomfort to surrounding people other than the listener. These situations are
This can be prevented by performing reproduction that suppresses sound leakage.

As shown in FIG. 5, a conventional coded signal reproducing apparatus for suppressing sound leakage during reproduction uses a quantized band signal (quantized band signal) S from an input coded signal S51.
A demultiplexer 51 for outputting the scale factor S53 in parallel with the demultiplexer 52, an inverse quantization means 52 for performing inverse quantization on each of the quantized band signals S52 and outputting a band signal S54, and a plurality of band signals S54. And a reproduction filter S53 for outputting a reproduction signal S55, and an attenuation filter 54 for attenuating the level of a band where the sound leakage of the reproduction signal S55 is large.

[0006] The synthesis filter means 53 synthesizes a plurality of bands by inverse DCT when the original signal is divided into a plurality of band signals by, for example, DCT at the time of encoding.

In this device, first, the demultiplexer 51
Extracts a quantization band signal S52 and a scale factor S53 from the input coded signal S51 and outputs the same. Next, the inverse quantization means 52 performs inverse quantization using the quantized band signal S52 and the scale factor S53, and outputs a band signal S54. Next, the synthesis filter means 53 outputs the plurality of band signals S
The reproduced signal S55 is output by synthesizing the reproduced signal S55, and the attenuation filter means 54 attenuates the level of the band of the reproduced signal S55 in which sound leakage is large, and outputs the reproduced signal S56 in which sound leakage is suppressed.

As shown in FIG. 6, for example, as shown in FIG. 6, the attenuation filter means 54 has an attenuation level at a frequency (6 kHz) showing a maximum level in the sound leakage frequency characteristic (-12d).
B) has a frequency versus attenuation level characteristic as a notch filter.

[0009]

However, the conventional encoded signal reproducing apparatus is provided with an attenuating filter means for attenuating the level of a band of a reproduced signal in which sound leakage is large in order to suppress sound leakage from headphones. Is required, which causes problems such as an increase in circuit scale and an increase in the amount of calculation.

SUMMARY OF THE INVENTION The present invention is to solve such a conventional problem, and to provide an encoded signal reproducing apparatus which can suppress sound leakage of a reproduced signal with a simple circuit configuration and with a small amount of operation. It is an object.

[0011]

SUMMARY OF THE INVENTION Accordingly, the present invention provides a coded signal reproducing apparatus for reproducing an original signal from a coded signal which has been band-divided and coded. And a demultiplexer for extracting a scale factor indicating level information for each group in which the quantized band signals are combined, and an inverse quantizer for performing inverse quantization using the scale factor and the quantized band signal and outputting a band signal. Converting means, band signal attenuating means for attenuating the level of the band signal having a large sound leakage using an attenuation coefficient, and synthesizing filter means for synthesizing the band signal output from the band signal attenuating means and reproducing the original signal. Provided.

Further, there is provided an attenuation coefficient correction means for correcting the attenuation coefficient based on the maximum value of the band signal output from the inverse quantization means.

Further, a demultiplexer for extracting a quantized band signal and a scale factor indicating level information for each group in which a plurality of quantized band signals are put together from the encoded signal, and a demultiplexer for extracting a band signal having a large sound leak. Scale factor attenuating means for attenuating a scale factor using an attenuation coefficient, and inverse quantization means for performing inverse quantization using the scale factor and the quantized band signal output from the scale factor attenuating means and outputting a band signal And synthesis filter means for synthesizing the band signal output from the inverse quantization means and reproducing the original signal.

Further, there is provided an attenuation coefficient calculating means for setting these attenuation coefficients in conjunction with the reproduction volume.

[0015]

Therefore, in the apparatus provided with the band signal attenuating means, the band signal is multiplied by the attenuation coefficient, and the level of the band signal with large sound leakage is attenuated. Then, the band signals are synthesized, and an audio signal in which sound leakage is suppressed is reproduced.

Further, in the apparatus provided with the scale factor attenuating means, the scale factor is multiplied by the attenuation coefficient to attenuate the scale factor of the group including the band signal having a large sound leakage. The level drops. Then, the band signals are synthesized,
An audio signal with suppressed sound leakage is reproduced.

In the apparatus provided with the attenuation coefficient correction means and the attenuation coefficient calculation means, the attenuation increases when the maximum value or the reproduction volume of the band signal is high, and decreases when the maximum value or the reproduction volume is low. The damping coefficient is changed. as a result,
Even when the level of a band with large sound leakage is high, the amount of attenuation can be increased to sufficiently suppress sound leakage, and when the original signal level is low, the amount of attenuation can be reduced to maintain reproduction sound quality.

In these devices, the circuit scale is small and the amount of calculation is small as compared with the case where an attenuation filter is provided.

[0019]

【Example】

(First Embodiment) As shown in FIG. 1, a coded signal reproducing apparatus according to a first embodiment is a demultiplexer 1 for outputting a quantization band signal S2 and a scale factor S3 in parallel from an input coded signal S1. Inverse quantization means 2 that performs inverse quantization on each of the quantized band signals S2 and outputs a band signal S4
A band signal attenuating means 3 for attenuating the level of the band signal having a large sound leakage in the band signal S4; and a synthesizing filter means 4 for synthesizing the band signal S5 output from the band signal attenuating means 3. .

In this device, first, the demultiplexer 1
Extracts a quantized band signal S2 and a scale factor S3 from the input coded signal S1, and outputs the same. Next, the inverse quantization means 2 performs inverse quantization using the quantized band signal S2 and the scale factor S3, and outputs a band signal S4.

The band signal attenuating means 3 holds an attenuation coefficient having a frequency-to-attenuation level characteristic shown in FIG. 6, and this attenuation coefficient and the band signal S4 output from the inverse quantization means 2 are stored.
To attenuate the level of the band signal having a large sound leakage in the band signal S4. Subsequently, the synthesis filter means 4
Is the band signal S output from the band signal attenuating means 3.
5, and outputs a reproduced signal S6 in which sound leakage is suppressed.

As described above, in the coded signal reproducing apparatus of the first embodiment, the band signal attenuating means 3 is provided to attenuate the level of a band signal having a large sound leak, and the band signal is synthesized to suppress the sound leak. Play the audio signal. Since the band signal attenuating means 3 is configured to multiply the band signal by the attenuation coefficient, the circuit scale can be reduced as compared with the case where an attenuation filter requiring a large number of multipliers, delay units and adders is provided. Also, the amount of calculation is small.

(Second Embodiment) The encoded signal reproducing apparatus of the second embodiment selectively attenuates the scale factor in order to suppress sound leakage. As shown in FIG. 2, the apparatus includes a demultiplexer 21 that outputs a quantization band signal S22 and a scale factor S23 in parallel from an input encoded signal S21.
And a scale factor attenuating means 23 for attenuating a scale factor of a group including a band signal having a large sound leakage, and performing inverse quantization on the quantized band signal S22 using the scale factor S24 output from the scale factor attenuating means 23. An inverse quantization unit 22 and a synthesis filter unit 24 that synthesizes the band signal S25 output from the inverse quantization unit 22 are provided.

In this device, when the demultiplexer 1 extracts and outputs the quantization band signal S22 and the scale factor S23 from the input encoded signal S21, the scale factor attenuating means 23 outputs the scale factor S23 and the scale factor S23. By multiplying by the attenuation coefficient held in the attenuation means 23, the scale factor of the group including the band signal having a large sound leakage is attenuated.

The inverse quantization means 22 generates a quantization band signal S22
And the scale factor S24 output from the scale factor attenuating means 23 to perform inverse quantization to output a band signal S25. The synthesis filter means 24 synthesizes the band signal S25 and outputs a reproduced signal S26 in which sound leakage is suppressed.

As described above, in the coded signal reproducing apparatus according to the second embodiment, the scale factor attenuating means 23 is provided to attenuate the scale factor of a group including a band signal having a large sound leakage, thereby causing a large sound leakage. Decrease the level of the band signal. Then, the band signal is synthesized to reproduce a sound signal in which sound leakage is suppressed. Since the scale factor attenuating means 23 has a configuration in which the scale factor is multiplied by the attenuation coefficient, the circuit scale is small and the amount of calculation is small as compared with the case where an attenuation filter is provided.

(Third Embodiment) The coded signal reproducing apparatus according to the third embodiment can sufficiently attenuate a band with a large sound leakage even when the level of the band is high. As shown in FIG. 3, the apparatus includes an attenuation coefficient correcting means 35 for giving a corrected attenuation coefficient to the band signal attenuating means 33. Other configurations are the same as those of the first embodiment.

In this device, the inverse quantization means 32 performs inverse quantization using the quantized band signal S32 output from the demultiplexer 31 and the scale factor S33, and outputs a band signal S34. The means 35 detects the maximum value of the band signal from the dequantized band signal S34, and corrects the held attenuation coefficient according to this value.

At this time, the attenuation coefficient correction means 35 holds the attenuation coefficient as a function of the maximum value in the band signal having a large sound leakage in the band signal S34, and when the maximum value is large, the attenuation coefficient is set to the large value. When the maximum value is small, the attenuation coefficient is corrected to a small value.

The attenuation coefficient correction means 35 outputs the corrected attenuation coefficient S37 to the band signal attenuation means 33. The band signal attenuation means 33 outputs the band signal S34 and the attenuation coefficient S37 corrected by the attenuation coefficient correction means 35. And the band signal S
In 34, the level of the band signal having a large sound leak is attenuated, and a band signal S35 in which the sound leak is suppressed is output. The synthesis filter means 34 synthesizes the band signal S35 in which the sound leakage is suppressed,
A reproduction signal S36 in which sound leakage is suppressed is output.

When the maximum value of the band signal is high, it is considered that the maximum level of the band signal having a large sound leakage is also high. However, in such a case, the coded signal reproducing apparatus of the third embodiment has the attenuation coefficient correcting means 35 in such a case. Corrects the attenuation coefficient to a large value, so that the attenuation of the band signal having a large sound leakage greatly increases, and the sound leakage in the reproduced sound can be sufficiently suppressed.

(Fourth Embodiment) The coded signal reproducing apparatus of the fourth embodiment changes the attenuation coefficient according to the reproduction volume. As shown in FIG. 4, this apparatus uses a reproduction volume level signal S47 to attenuate the level of a band signal by an attenuation coefficient S.
An attenuation coefficient calculating means 45 for calculating 48 is provided. Other configurations are the same as those of the first embodiment.

In this device, first, the demultiplexer 41
Extracts and outputs the quantization band signal S42 and the scale factor S43 from the input coded signal S41, and then inversely quantizes the inverse quantization using the quantization band signal S42 and the scale factor S43. Quantization is performed, and a band signal S44 is output.

The attenuation coefficient calculating means 45 uses the reproduction volume level signal S47 representing the level of the reproduction volume, and when the reproduction volume is large, the reproduction volume is increased so that the attenuation level of the band signal is increased. If it is smaller, an attenuation coefficient S48 for attenuating the level of the band signal is calculated and output so as to reduce the attenuation level of the band signal.

The band signal attenuating means 43 multiplies the inversely quantized band signal S44 by the attenuation coefficient S48 output from the attenuation coefficient calculating means 45, and generates a band signal having a large sound leakage among the band signals S44. The level is attenuated, and a band signal S45 in which sound leakage is suppressed is output. Then, the synthesis filter means 44 synthesizes the band signal S45 in which the sound leakage is suppressed, and outputs a reproduced signal S46 in which the sound leakage is suppressed.

As described above, in the coded signal reproducing apparatus according to the fourth embodiment, since the attenuation coefficient is linked to the reproduction volume, even when the reproduction volume is high, the band with large sound leakage can be sufficiently attenuated. . When the reproduction volume is low, the sound quality of the reproduction signal can be maintained by reducing the attenuation level of the band signal.

In the fourth embodiment, the band signal attenuating means is used.
Although the attenuation coefficient used in 43 is calculated according to the playback volume, the attenuation coefficient used in the scale factor attenuation means 23 of the second embodiment may be calculated according to the playback volume.

[0038]

As is apparent from the above description of the embodiment, the coded signal reproducing apparatus according to the present invention has a simple circuit configuration and a small amount of calculation to suppress sound leakage as compared with the conventional apparatus. Can be performed.

In a device for correcting the attenuation coefficient based on the maximum value of the band signal or setting the attenuation coefficient in conjunction with the reproduction volume, even if the level of the band where the sound leakage is large is high, the sound leakage is sufficiently suppressed. When the reproduction volume is low, the sound quality of the reproduction signal can be maintained by lowering the attenuation level, and such an operation can be performed with a simple circuit configuration and a small amount of calculation. Can be.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an encoded signal reproducing apparatus according to a first embodiment of the present invention;

FIG. 2 is a block diagram showing a configuration of an encoded signal reproducing apparatus according to a second embodiment of the present invention;

FIG. 3 is a block diagram showing a configuration of an encoded signal reproducing apparatus according to a third embodiment of the present invention;

FIG. 4 is a block diagram showing a configuration of an encoded signal reproducing apparatus according to a fourth embodiment of the present invention;

FIG. 5 is a block diagram showing a configuration of a conventional encoded signal reproducing device.

FIG. 6 is a characteristic diagram showing frequency versus attenuation level characteristics of an attenuation filter of a conventional device.

[Explanation of symbols]

 1, 21, 31, 41, 51 Demultiplexer 2, 22, 32, 42, 52 Inverse quantization means 3, 33, 43 Band signal attenuation means 4, 24, 34, 44, 53 Synthesis filter means 23 Scale factor attenuation means 35 Attenuation coefficient correction means 45 Attenuation coefficient calculation means 54 Attenuation filter means

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H03M 7/30 H03H 17/02 613

Claims (3)

(57) [Claims] 1. An encoded signal reproducing apparatus for reproducing an original signal from an encoded signal which has been band-divided and encoded, comprising: a group in which a quantized band signal and a plurality of quantized band signals are grouped from the encoded signal; A demultiplexer for extracting a scale factor indicating each level information; an inverse quantization means for performing inverse quantization using the scale factor and the quantized band signal to output a band signal; Band signal attenuating means for attenuating the level of the band signal using an attenuation coefficient, and a band signal output from the inverse quantization means for reducing the attenuation coefficient.
An attenuation coefficient correction means for correcting based on a maximum value of the signal, and a synthesis filter means for synthesizing a band signal output from the band signal attenuating means to reproduce an original signal. Playback device. 2. An encoded signal that has been band-divided and encoded.
In a coded signal reproducing apparatus for reproducing an original signal, a quantized band signal and a plurality of quantized band
Scale indicating the level information for each group of signals
A demultiplexer for extracting a factor, and using the scale factor and the quantized band signal.
Inverse quantization means for performing inverse quantization and outputting a band signal
And the level of the band signal having a large sound leakage using an attenuation coefficient.
Band signal attenuating means for attenuating the sound, and an attenuation coefficient calculating means for setting the attenuation coefficient in conjunction with the reproduction volume
Means leaving the band signal output from the band signal attenuation means synthesizes
And a synthesis filter means for reproducing the original signal.
Characterized coded signal reproducing device. 3. A coded signal reproducing apparatus for reproducing an original signal from an encoded signal which has been band-divided and encoded, comprising: a group in which a quantized band signal and a plurality of quantized band signals are grouped from the encoded signal. A demultiplexer for extracting a scale factor indicating level information for each level; a scale factor attenuating means for attenuating the scale factor of a group including the band signal having a large sound leakage by using an attenuation coefficient; Damping coefficient calculation set in conjunction with
Means out, the scale factor scale factor output from the attenuating means and performs inverse quantization using said quantization-band signal, and inverse quantization means for outputting a band signal is output from the inverse quantization means And a synthesis filter means for synthesizing the band signal obtained and reproducing the original signal.