JP2006243042A - High-frequency interpolating device and reproducing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-frequency interpolating device capable of high-frequency interpolation suitable to an original sound source by making good use of features of the original sound source. <P>SOLUTION: The high-frequency interpolating device is equipped with a means 40 of performing 1/2 down sampling of a source digital sound signal, a means 41 of performing 2-time up sampling of the 1/2 down-sampled digital sound signal, and a digital low-pass filter 42 of filtering the 2-time up-sampled digital sound signal, and interpolates the high-frequency band of the source digital sound signal. Further, the high-frequency interpolating device is equipped with a 1st attenuating means 45 of attenuating the level of the source digital sound signal, a 2nd attenuating means 43 of attenuating the level of the digital sound signal filtered by the digital low-pass filter 42, and a means 44 of adding digital sound signals attenuated by the 1st attenuating means 45 and 2nd attenuating means 43, and outputs the addition digital sound signal generated by the adding means 44. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a high-frequency interpolator that interpolates a high-frequency band of a compressed digital audio signal such as MD (Mini Disc), MP3 (MPEG (Moving Picture Experts Group 1) Audio layer 3), DAB (Digital Audio Broadcasting), and the like, and The present invention relates to a playback device that includes this high-frequency interpolation device and plays back a digital audio signal.

In the case of CD (Compact Disc), the acoustic signal is a stereo signal having a sampling frequency of 44.1 kHz and a data bit length of 16 bits. The amount of information can be represented by the number of bits required per second, and is 1411.2 kbps for a CD.
In the case of MD, data to be encoded by ATRAC (Advanced TRansform Acoustic Coding), which is a compression technique that thins out components that are difficult to hear and data before and after a loud sound, using human auditory characteristics, and ATRAC3, which is an improved version thereof. We are reducing the amount. ATRAC3 supports data compression ratios of 2 times (MDLP2, 132 kbps) and 4 times (MDLP4, 66 kbps) of ATRAC, and can compress up to about 1/20 as compared with CD. The sound quality decreases as the compression rate increases.

  The human audible frequency band is said to be 20 Hz to 20 kHz, but there are individual differences, and for an ordinary person, the upper limit is considered to be about 14 k to 15 kHz. A compression technique has been developed in consideration of such an audible frequency band, but a pure tone (sine wave) is used for measurement of the audible frequency band. However, the idea that actual music and natural sounds are mixed with sounds of a plurality of frequencies, and sounds outside the audible band that cannot be heard alone are also affecting the sense of hearing due to the spread of the sound.

Patent Documents 1 and 2 disclose a frequency thinning device that deletes one of a pair of bands having a strong correlation from the spectrum distribution of a signal to be thinned and closes the spectrum in the other band to the low frequency side. Yes.
In Patent Document 3, when it is necessary to interpolate a signal, a portion of the spectrum of the signal to be interpolated, where the correlation of the spectrum distribution is high, is placed on the high frequency side of the signal to be interpolated along the envelope. In addition, a frequency interpolation system that extends the bandwidth is disclosed.

In Patent Document 4, a spectrum of a limited band corresponding to a predetermined frequency band of an input time-series signal is encoded, and on the decoding side, a time-series signal of a frequency band to be expanded is mapped to the spectrum of the limited band. Therefore, a signal coding apparatus is disclosed that adaptively creates mapping information indicating a mapping method and outputs the encoded spectrum of the limited band and the mapping information.
Japanese Patent No. 3576941 Japanese Patent No. 3576951 Japanese Patent No. 3576942 JP 2004-80635 A Japanese Patent Laid-Open No. 2001-127637

When a digital audio signal is compressed and recorded at a high compression rate, for example, in MDLP4, as shown in FIG. 6B, the frequency spectrum exists only up to about 12 kHz, and the CD signal shown in FIG. Even in comparison, there is a problem that high frequency information is lost.
In view of the above-described circumstances, the present applicant has down-sampled the compressed and expanded digital sound signal by 1/2, then up-sampled twice, and double-sampled the digital sound signal by digital low pass. A high-frequency interpolator that filters with a filter and interpolates the high-frequency band of the original digital audio signal is filed on the same day.

  However, when an MD sound source having a spectrum as shown in FIG. 7A is high-frequency interpolated by this high-frequency interpolation device, the high frequency as shown in FIG. 7B is excessively emphasized depending on the MD sound source. The sound source may have a spectrum. When this sound source is reproduced as it is, that is, with the MD sound source ratio 0 and the high frequency interpolation sound source ratio 1 without mixing or the like, the spectrum in which the high frequency band A as shown in FIG. There is a problem that it may be heard as “Kasa Kasa”.

The present invention has been made in view of the circumstances as described above. In the first to third aspects of the invention, it is possible to perform high-frequency interpolation suitable for the original sound source by making use of the characteristics of the original sound source. An object of the present invention is to provide an area interpolation device.
In the fourth aspect of the invention, it is an object of the present invention to provide a playback device including a high-frequency interpolation device capable of performing high-frequency interpolation suitable for the original sound source by making use of the characteristics of the original sound source.

  The high-frequency interpolation apparatus according to the first aspect of the invention comprises means for down-sampling the original digital audio signal by 1/2, means for up-sampling the digital audio signal down-sampled by 1/2 by the means, and means for A high-pass interpolating apparatus for interpolating a high frequency band of the original digital sound signal, wherein the first low-pass filter attenuates the level of the original digital sound signal. Attenuating means; second attenuating means for attenuating the level of the digital acoustic signal filtered by the digital low pass filter; and means for adding the digital acoustic signals attenuated by the first attenuating means and the second attenuating means. The digital sound signal added by the means is output.

  In this high-frequency interpolator, the means for down-sampling by 1/2 reduces the original digital audio signal by 1/2, and the means for up-sampling twice doubles the digital audio signal by 1/2 down-sampling. To do. A digital low-pass filter filters the digital sound signal that has been up-sampled twice, and interpolates the high frequency band of the original digital sound signal. The first attenuation means attenuates the level of the original digital acoustic signal, and the second attenuation means attenuates the level of the digital acoustic signal filtered by the digital low-pass filter. The adding means adds the digital sound signals attenuated by the first attenuation means and the second attenuation means, and outputs the added digital sound signals.

  According to a second aspect of the present invention, the digital low-pass filter is a digital filter that performs oversampling processing. The band-limited original analog sound signal and the original analog sound signal are converted to analog and converted to analog. Parameters are calculated by solving a conditional expression set to design an IIR (Infinite Impulse Response) filter so as to reduce an error signal with an analog acoustic signal by sample value H∞ control based on a predetermined condition. It is characterized by being.

  In this high-frequency interpolation device, the digital low-pass filter is a digital filter that performs oversampling processing. This digital low-pass filter is an IIR (Infinite Impulse Response) type so that an error signal between the band-limited original analog sound signal and the analog sound signal obtained by digital conversion of the original analog sound signal and then analog conversion becomes small. A conditional expression is set to design the filter, and the parameter is calculated by solving the set conditional expression by the sample value H∞ control based on a predetermined condition.

  The high-frequency interpolation apparatus according to a third aspect of the invention is characterized in that each attenuation rate of the first attenuation means and the second attenuation means can be adjusted.

  This high-frequency interpolation device is configured to be able to adjust each attenuation rate of the first attenuation means and the second attenuation means.

  A playback device according to a fourth aspect of the present invention includes the high frequency interpolating device according to any one of claims 1 to 3, and is a high frequency of a digital acoustic signal read from a recording medium or a digital acoustic signal received from the outside. The band is interpolated by the high-frequency interpolating device to reproduce the digital acoustic signal.

  The reproduction apparatus includes the high frequency interpolating device according to any one of claims 1 to 3, and a high frequency band of a digital audio signal read from a recording medium or a digital audio signal received from the outside is set to a high frequency band. The digital sound signal is reproduced by interpolating with an interpolating device.

  According to the high-frequency interpolation apparatus according to the first aspect of the present invention, it is possible to realize a high-frequency interpolation apparatus capable of performing high-frequency interpolation suitable for the original sound source by making use of the characteristics of the original sound source.

  According to the high-frequency interpolation apparatus according to the second aspect of the present invention, it is possible to realize a high-frequency interpolation apparatus capable of performing high-frequency interpolation suitable for the original sound source by utilizing the characteristics of the original sound source. Further, when high-frequency interpolation is performed on a compressed digital audio signal, a frequency spectrum close to the original sound before compression can be obtained, and high-frequency interpolation closer to the original sound can be executed.

  According to the high-frequency interpolation apparatus according to the third aspect of the invention, it is possible to perform high-frequency interpolation suitable for the original sound source by making use of the characteristics of the original sound source, and to perform high-frequency interpolation according to the user's preference A high-frequency interpolation device can be realized.

  According to the playback device of the fourth aspect of the present invention, it is possible to perform high-frequency interpolation suitable for the original sound source by making use of the characteristics of the original sound source. It is possible to realize a playback device that can obtain a playback sound close to the previous original sound.

Hereinafter, the present invention will be described with reference to the drawings showing embodiments thereof.
(Embodiment 1)
FIG. 1 is a block diagram showing the main configuration of Embodiment 1 of a high frequency control device according to the present invention.
In this high-frequency interpolating apparatus, the 1/2 down-sampling unit 40 down-samples a compressed and expanded digital acoustic signal as schematically shown in FIG. As shown in FIG. The 1/2 downsampled digital audio signal is supplied to the double upsampling unit 41.

  The double upsampling unit 41 upsamples a given digital audio signal twice, and inserts a sampling point with a sampling value of 0 in the middle of each sampling value as shown in FIG. ). In the digital acoustic signal that has been upsampled twice, for example, a line-symmetric spectrum (imaging) having an axis of symmetry of 11 kHz (when the original sampling frequency is 44.1 kHz) is generated.

The digital acoustic signal that has been upsampled by the double upsampling unit 41, including the imaging component, is supplied to an IIR type or FIR (Finite Impulse Response) type digital low-pass filter and subjected to oversampling. The oversampling process includes a double upsampling process of the double upsampling unit 41.
As shown in FIG. 3D, the digital sound signal is interpolated by sampling over the sampling point by the zero interpolation by the oversampling process to generate a high frequency component.

The digital sound signal oversampled by the double upsampling unit 41 and the digital low-pass filter 42 is supplied to a digital attenuator 43 (second attenuation means) having a gain k (0 ≦ k ≦ 1) and attenuated. This is given to the adding unit 44.
On the other hand, the original compressed and expanded digital acoustic signal is given to a digital attenuator 45 (first attenuating means) having a gain 1-k (0 ≦ k ≦ 1), attenuated, and given to the adding unit 44. .

The adder 44 adds the digital acoustic signals given from the digital attenuator 43 and the digital attenuator 45 and outputs the result as a digital acoustic signal in which the high frequency band is interpolated.
The gains k and 1-k can be changed in conjunction with each other by an external operation. Even when the gains are changed, the sum is set to 1 so that the level of the added digital sound signal is substantially constant. Yes.

When an MD sound source having a spectrum as shown in FIG. 4A is interpolated at high frequency by the 1/2 down-sampling unit 40, double up-sampling unit 41 and digital low-pass filter 42 of such a high-frequency interpolating device, FIG. In some cases, the sound source has a spectrum in which the high frequency range is excessively emphasized as shown in 4 (b). Even in such a case, for example, when mixing and reproduction is performed such that the proportion of the MD sound source is 0.3 and the proportion of the sound source after high-frequency interpolation is 0.7, the high frequency band B as shown in FIG. It can be set as a reproduced sound having an appropriate spectrum that is not emphasized too much.
Note that the processing target of this high-frequency interpolation device is not limited to a compressed and expanded digital acoustic signal, and the same applies when applied to high-frequency interpolation of a digital acoustic signal that does not have a high-frequency band. It is possible to obtain action and effect.

FIG. 2 is a block diagram of a signal restoration system model showing a method for calculating the parameters of the digital low-pass filter 42.
In this signal restoration system model, an analog signal from the signal model 50 having a function F (s) serving as a model of the frequency characteristic of the band-limited original analog signal is converted into a digital signal by the A / D converter 51, The converted digital signal is upsampled M (M is an integer of 2 or more) times by the upsampling unit 52.

The digital signal that has been up-sampled M times is supplied to the digital low-pass filter 53 and subjected to oversampling processing. The oversampled digital signal is converted into an analog signal by the D / A converter 54, filtered by the post filter 55 having the characteristic P (s), and then supplied to the subtractor 56.
The subtracting unit 56 calculates and outputs an error signal e between the analog signal (which is delayed in some cases) from the signal model 50 and the analog signal filtered by the post filter 55.

When calculating the parameters of the digital low-pass filter 42, a conditional expression is set to design the IIR type digital low-pass filter 53 so that the error signal e becomes small in the signal restoration system model as described above. Next, a calculation formula obtained by approximately converting the conditional expression into a finite-dimensional discrete-time system is obtained, and the obtained calculation formula is solved by H∞ control based on a predetermined condition, whereby the digital low-pass filter 53 (digital low-pass filter 42). Parameters are calculated.
The digital low-pass filter obtained as described above is an IIR type, but in digital signal processing, an FIR type filter is often used because of easy programming and mounting. In that case, it can be accurately realized as an FIR filter by calculating the impulse response of the derived IIR filter.

  In the digital low-pass filter design method as described above, the characteristic P (s) of the analog component such as the post filter 55 is also taken into account, and these analog characteristics are obtained between sampling points by lifting of the sample value control theory. The information is discretized (digitized) in such a way that it is not lost. Therefore, optimization design including the response between sampling points is possible. Refer to Patent Document 5 for details of this design method.

(Embodiment 2)
FIG. 5 is a block diagram showing a configuration of an optical disc apparatus which is an embodiment of a reproducing apparatus according to the present invention. This optical disc device is a recordable / reproducible mini disc device. In a state where a rectangular flat cartridge 12 containing the mini disc 11 is loaded in the mini disc device, the shutters on both sides of the cartridge 12 are opened and the mini disc is opened. 11, when the optical pickup 15 reads and records from one surface through the objective lens 14, a magnetic field by the magnetic head 19 is applied to the other surface of the mini disk 11.

  The mini disk 11 is rotationally driven by the spindle motor 13 so as to have a predetermined constant linear velocity, and the optical pickup 15 is driven by the feed motor 16 and moves in the radial direction of the mini disk 11. The magnetic head 19 is driven by the head drive unit 20 during recording and moves in the radial direction of the mini-disc 11, and the position of the magnetic head 19 is controlled so as to sandwich the same track with the optical pickup 15 from both sides.

The spindle motor 13, the optical pickup 15 and the feed motor 16 are driven and controlled by a servo control unit 17. The servo control unit 17 includes a tracking control unit 32 and a focus control unit 33.
The signal detected by the optical pickup 15 is sent to an RF (Radio Frequency) amplifier 22 and amplified. Of the signals amplified by the RF amplifier 22, the focus error signal and the tracking error signal are sent to the servo control unit 17 and given to the focus control unit 33 and the tracking control unit 32.

Of the signals amplified by the RF amplifier 22, the address signal is sent to the address decoder 21, decoded, and given to the encoder / decoder 23.
The address signal sent to the encoder / decoder 23 and decoded is used for position control of the magnetic head 19 by the head drive unit 20 and also sent to the system controller 18 for spindle motor 13 and optical pickup 15 by the servo control unit 17. And used for drive control of the feed motor 16 and the like.

The data signal among the signals amplified by the RF amplifier 22 is sent to the encoder / decoder 23, decoded, and sent to the DRAM 25 (Dynamic Random Access Memory) through the anti-vibration memory controller 24. The data (digital acoustic signal) sent to the DRAM 25 is temporarily stored and then sent to the acoustic compression encoder / decoder 26 through the anti-vibration memory controller 24.
The acoustic compression encoder / decoder 26 decompresses the sent data and supplies it to the high frequency interpolating unit 34 which is a high frequency interpolating device according to the present invention.
The high-frequency interpolation unit 34 performs high-frequency interpolation of the given data (digital acoustic signal) as described in the first embodiment, and the high-frequency interpolated digital acoustic signal is subjected to D / A conversion. It is output through the device 28.

  The digital acoustic signal input through the A / D converter 27 is acoustically compressed and encoded by the acoustic compression encoder / decoder 26, and sent to the DRAM 25 through the vibration proof memory controller 24. The data sent to the DRAM 25 is temporarily stored, then sent to the encoder / decoder 23 through the vibration proof memory controller 24, coded, and recorded on the mini disk 11 by the magnetic head 19 and the optical pickup 15.

The vibration-proof memory controller 24 and the DRAM 25 prevent sound skipping due to vibration or the like by using the difference between the time required for storage in the DRAM 25 and the time required for reading from the DRAM 25.
The system controller 18 is connected to the display unit 29, the clock circuit 30, and the operation unit 31, and controls the operation of the servo control unit 17, the encoder / decoder 23, and the anti-vibration memory controller 24. The designated information is displayed on the display unit 29.

It is a block diagram which shows the principal part structure of embodiment of the high region control apparatus which concerns on this invention. It is a block diagram of a signal restoration system model showing a method for calculating parameters of a digital low-pass filter. It is a typical waveform diagram for demonstrating operation | movement of the high region control apparatus which concerns on this invention. It is explanatory drawing which shows operation | movement of the high region control apparatus which concerns on this invention. 1 is a block diagram showing a configuration of an optical disc apparatus that is an embodiment of a playback apparatus according to the present invention. It is a characteristic view which shows the frequency characteristic for demonstrating the necessity of a high region interpolation apparatus. It is explanatory drawing for demonstrating the subject which this invention tends to solve.

Explanation of symbols

11 Mini Disc 26 Acoustic Compression Encoder / Decoder 28 D / A Converter 34 High Frequency Interpolator (High Frequency Interpolator)
40 1/2 downsampling unit 41 double upsampling unit 42 digital low pass filter 43 digital attenuator (second attenuation means)
44 Adder 45 Digital attenuator (first attenuation means)
50 Signal Model 51 A / D Converter 52 Upsampling Unit 53 Digital Low-Pass Filter 54 D / A Converter 55 Post Filter 56 Subtracting Unit

Claims (4)

  Means for down-sampling the original digital audio signal by 1/2, means for up-sampling the digital audio signal down-sampled by 1/2 by the means, and filtering the digital audio signal up-sampled by the means twice A high-frequency interpolating device for interpolating a high-frequency band of the original digital audio signal, wherein the digital low-pass filter filters the first attenuation means for attenuating the level of the original digital audio signal A second attenuation means for attenuating the level of the digital sound signal; and means for adding the digital sound signals attenuated by the first attenuation means and the second attenuation means, and outputting the added digital sound signal. A high-frequency interpolating device characterized in that it should be done.   The digital low-pass filter is a digital filter that performs oversampling processing, so that an error signal between the band-limited original analog sound signal and the analog sound signal that has been converted from the original analog sound signal to analog is reduced. The high-frequency interpolating apparatus according to claim 1, wherein the parameter is calculated by solving a conditional expression set to design an IIR (Infinite Impulse Response) filter by a sample value H∞ control based on a predetermined condition.   The high-frequency interpolation apparatus according to claim 1 or 2, wherein each attenuation rate of the first attenuation means and the second attenuation means is adjustable.   A high-frequency interpolation device according to any one of claims 1 to 3, comprising a digital acoustic signal read from a recording medium or a high-frequency band of a digital acoustic signal received from the outside by the high-frequency interpolation device. A playback apparatus characterized in that the digital sound signal is played back.

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