JP2006067550A - Digital audio signal processing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an audio signal processing apparatus which selects a filter corresponding to a composition of playing a piece of music. <P>SOLUTION: A sound source of a main melody of a vocal or the like is localized in the center ordinarily in a piece of music by band play of a small composition, thereby increasing audio signal components of sound images localized in the center. There are a number of sound sources in a piece of music of a great composition like an orchestra and such a piece of music is played in a wide recording space such as a hall, thereby reducing audio signal components of sound images localized in the center. Outputs of a sharp roll-off characteristic filter and a slow roll-off characteristic filter are switched for an inputted audio signal in accordance with a ratio of audio signal components localized in the center. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a digital audio signal processing apparatus that improves the sound quality and the like of digital audio signal reproduction.

  Filter processing is performed to improve the sound quality of digital audio signal reproduction represented by CD (compact disc) and digital audio broadcasting. Examples of filters used for the filter process include a slow roll-off characteristic filter and a sharp roll-off characteristic low-pass filter.

  An example of the slow roll-off characteristic filter is a data interpolation digital filter. The data interpolation digital filter interpolates data between sampling data based on a digital audio signal to generate high sampling data. When this data interpolation digital filter is applied to a digital audio signal, high frequency components are increased by interpolating the data. The audio signal processed by this filter has a characteristic that the high sound range can be reproduced more naturally and in a stretched manner, and the sound field can be reproduced with the sound field spreading in the left-right depth direction. On the other hand, there is a feature that the sound attack / rise is weak and the sound field cannot be heard to appear forward. This feature is suitable for music that is played by a wide variety of musical instruments and in which audio signals are uniformly included from low to high frequencies, especially orchestral music with a large organization.

  The sharp roll-off characteristic low-pass filter removes out-of-band noise with a low-pass filter having an acute attenuation characteristic. When this sharp roll-off characteristic low-pass filter is applied to a digital audio signal, a high-frequency component is suppressed and a middle-low frequency component is output. The audio signal processed by this filter has the characteristics that the outline of the sound becomes clear, the sound attack / rise is strong, and the sound field can be reproduced in the forward direction. On the other hand, it is inferior in the expansion of the high sound range, and has a feature that the sound field does not spread in the left-right depth direction. This feature makes it possible to reproduce music that emphasizes the mid-low range with a small musical instrument structure and makes the outline of the sound clear, especially for small bands centered on vocals and sound reproduction of movies. Is suitable.

  As described above, there are suitable filters and unsuitable filters depending on the characteristics of the audio signal such as the composition of the musical piece and the composition of the musical piece. In order to solve such a problem, there is a technique of selecting a filter according to an audio signal.

  The audio device of Patent Document 1 has a plurality of digital low-pass filters, and selects and outputs one of the digital low-pass filters by comparing the output of each filter with the output of the original data.

Japanese Laid-Open Patent Publication No. 11-232790

  In the case of a data interpolation digital filter that generates high-sampling data, as described above, the attack / rise is weak and the sound field does not sound like coming out forward, so it consists of a small instrument organization mainly composed of vocals. Not suitable for audio signals for small band performances. In addition, as described above, the sharp roll-off digital low-pass filter is not suitable for a large-scale audio signal such as an orchestra because the high-frequency range is inferior and the sound field does not spread in the left-right depth direction. .

  In the technique of Patent Document 1, since it is determined which filter is used based on the bandwidth in the high frequency direction included in the digital audio signal, the musical scale may be overlooked. For example, in a small band performance, an instrument that can output an audio signal having a high frequency component, such as a synthesizer, may be used. A musical piece played in such a band includes an audio signal having a high frequency component. When an appropriate digital low-pass filter is selected from a plurality of digital low-pass filters having different cutoff frequencies based on a high frequency component included in an audio signal as in the technique of Patent Document 1, a synthesizer as described above is used. Even in the case of an audio signal based on a small band performance including a high frequency component, a data interpolation digital filter that generates high sampling data may be selected. The audio signal filtered by the data interpolation digital filter is reproduced as a sound with a sense of breadth, but is not suitable for audio signal reproduction of a small band performance because it has a weak attack and rise.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an apparatus to which a digital filter suitable for knitting for playing music to be reproduced can be applied.

  The present invention has been made to achieve the above object, and is a digital audio signal output device to which at least a digital audio signal including an audio signal for localizing a sound image is input at the center, and filtering the digital audio signal And a slow roll-off characteristic digital filter that outputs the digital audio signal, a sharp roll-off characteristic digital filter that filters and outputs the digital audio signal, and a ratio of an audio signal component that localizes a sound image in the center of the digital audio signal is predetermined. A comparison / determination means for outputting information indicating a result of comparison / determination whether the value is greater than a value; an output from the slow roll-off characteristic digital filter according to the information indicating the result of comparison / determination; and the sharp roll-off characteristic Digital filter Characterized in that it comprises a switching means for outputting switching between et output.

  Further, according to the present invention, information related to a digital audio signal and a digital filter are associated and stored in a storage unit, and when the digital audio signal and the information related to the digital audio signal are input, the storage unit The digital filter associated with the information corresponding to the information related to the input digital audio signal is read, the digital audio signal filtered by the digital filter is output, and the operation of the arithmetic unit for selecting the digital filter is performed. It is characterized by being stopped.

  Specifically, for example, the digital audio signal output device further receives information on the input digital audio signal, and includes information on the digital audio signal and any one of the plurality of digital filters. Storage means for associating and storing information to be displayed, and when the storage means includes information relating to a digital audio signal that matches the information relating to the input digital audio signal, it corresponds to the information relating to the digital audio signal The information indicating the attached digital filter is read from the storage means, and the switching control means for outputting the information indicating the digital filter to the switching means, the storage means coincides with the information relating to the digital audio signal input to the storage means. For digital audio signal And a switching unit that stops the operation of the comparison determination unit, and the switching unit switches to the output from the digital filter indicated by the information output from the switching control unit. It is characterized by that.

  According to the audio signal output device of the present invention, digital filters having different characteristics can be quickly switched in accordance with the music source, particularly the composition in which the music is played. Thereby, it is possible to output an audio signal having both a sense of depth / expansion and a sense of attack / extrusion with a single audio signal output device.

  A general digital audio signal will be described. Usually, when playing music, for example, if a band performance is organized such as guitar, vocal, synthesizer, there are sound sources at various positions, such as vocal in the center, synthesizer on the left, and guitar on the right. The human ear can recognize the position of the sound source when listening to the sound. In order to reproduce this, the sound output from the speaker system is heard from a predetermined place. This place is called localization. Usually, a digital audio signal is positioned between a left channel audio signal, which is a left sound source, and a right channel audio signal, which is a right sound source, in order to localize the sound image and to continuously spread the sound image to the left and right. The center channel audio signal that is the sound source of the center is localized. As an example of such an audio signal reproduction method, there is a two-channel output stereo reproduction method. In this reproduction system audio signal, a left channel audio signal and a right channel audio signal are downmixed with a center channel audio signal having the same sound source and the same phase. Here, a two-channel signal obtained by down-mixing will be described as a left track audio signal and a right track audio signal.

Here, “L” indicates a left channel audio signal, “R” indicates a right channel audio signal, and “C” indicates a center channel audio signal. “L _T ” indicates a left track audio signal, and “R _T ” indicates a right track audio signal. “NC _L ” indicates a center channel component included in the left track audio signal. “NC _R ” indicates a center channel component included in the light track audio signal. Here, “n” is a multiplier (0.1 to 1), “n” of “nC _L ” indicates the ratio of the center channel component “C _L ” included in “L _T ”, and “nC _R ” “N” in FIG. 4 indicates the ratio of the center channel component “C _R ” included in “R _T ”. In this case, the left track audio signal can be represented by “L _T = L + nC _L ”, and the right track audio signal can be represented by “R _T = R + nC _R ”.

In order to localize the center sound image with a stereo reproduction system audio signal of 2-channel output, as described above, the center sound source is allocated to the left sound source and the right sound source. In the example of a band performance of a synthesizer as the left sound source, vocals and bass as the center sound source, and guitar as the right sound source, the left track audio signal “L _T ” includes the synthesizer audio signal and the vocal audio signal. The base audio signal and the light track audio signal “R _T ” include a guitar audio signal, a vocal audio signal, and a base audio signal. When such an audio signal is reproduced by an audio reproduction device or the like, vocal and bass sounds can be heard between the synthesizer sound and the guitar sound at positions equidistant from the speakers of the two channels. At this time, for example, if each of the vocal audio signal component and the bass audio signal component is equally included in each of “nC _L ” and “nC _R ”, the vocal and bass sounds are heard from the center. For example, if the vocal audio signal component is equally included in each of “nC _L ” and “nC _R ”, and the base audio signal component is included in “nC _R ” more than “nC _L ”, The sound is heard from the center, and the bass sound is heard at the position where it is swung to the right from the center. As described above, when the sound is heard from the center, the components included in “nC _L ” and the components included in “nC _R ” largely coincide with each other. In addition, when the sound is heard from the center to the right or left, the ratio of the component included in “nC _L ” and the component included in “nC _R ” is relatively small.

In general, in the case of a music signal of a music piece with a small band performance, the sound source of the main melody such as vocals is localized in the center without being swung left and right, so that “nC _L ”, “nC _L ” _R ”contains a lot of the same sound source and in-phase components.

On the contrary, in the case of a music signal of a music piece performed by a performance such as an orchestra having a large organization, since there are many musical instruments as sound sources, the sound source positions are dispersed, and as a result, the component in which the sound image is localized is reduced in the center. In addition, music performed by orchestras with large organization is recorded in a relatively wide recording space such as a hall, but the audio signal recorded in such a place is out of phase due to reflected sound from the floor or walls. For example, since the sound source positions are dispersed such that only a specific sound can be heard swaying to the left, the component in which the sound image is localized in the center is reduced. For this reason, the audio signal of a musical piece by a performance of an orchestra or the like having a large organization has few in-sound source / in-phase components in “nC _L ” and “nC _R ”.

Therefore, it is possible to estimate the composition in which the music piece is played based on the ratio of the components of “nC _L ” and “nC _R ” with respect to the audio signal of the music piece.

The digital audio signal processing apparatus according to the present embodiment estimates the composition in which the music piece is played based on the ratio of audio signal components centered in the center of the input digital audio signal, and provides a filter output suitable for the composition. To choose.
<First Embodiment>
First, the first embodiment will be described. FIG. 1 shows an example of a digital audio signal processing apparatus for carrying out the present invention. In FIG. 1, a digital audio signal processing apparatus 10 according to the present embodiment includes an input unit 11, a slow roll-off digital filter 12, a sharp roll-off digital filter 13, a first digital mixer 14, a second digital mixer 15, It comprises a comparison / determination unit 16, a HOLD unit 17, a filter switching unit 18, an output unit 19, and the like. Furthermore, in this embodiment, the microcomputer 20 and the user interface 21 shall be provided. The microcomputer 20 and the user interface 21 may be provided in the digital audio signal processing apparatus 10 or may be realized by using part or all of the functions of other apparatuses in the digital audio signal processing apparatus 10. Good.

  The first digital mixer 14, the second digital mixer 15, the comparison / determination unit 16, the HOLD unit 17, and the filter switching unit 18 may be realized by dedicated hardware. It may be configured by a memory and a CPU (central processing unit), and the function may be realized by loading a program for realizing the function of each unit into the memory and executing it.

  Each part of the digital audio signal processing apparatus 10 will be described. A digital audio signal is input to the input unit 11 from the outside (not shown). Examples of the source of the input digital audio signal include a CD and a digital audio broadcast. The digital audio signal input from the input unit 11 is input in parallel to the slow roll-off digital filter 12, the sharp roll-off digital filter 13, the first digital mixer 14, and the second digital mixer 15.

  The slow roll-off type digital filter 12 is a filter having a linear phase characteristic. Here, it is assumed that the slow roll-off digital filter 12 is a data interpolation digital filter that interpolates a digital audio signal between sampling data and generates high sampling data. The data interpolation digital filter is realized by, for example, a Lagrange interpolation formula. As the complement order is increased, more data is interpolated between the sampling data, and the audio signal passing through the filter has a smooth waveform. The slow roll-off digital filter 12 filters the input digital audio signal and outputs the filtered digital audio signal to the filter switching unit 18.

  The sharp roll-off type digital filter 13 is a filter having a characteristic that the level sharply decreases at the cutoff frequency. The sharp roll-off digital filter 13 is realized by, for example, an FIR (finite impulse response) calculation filter or an IIR (Infinite impulse Response) calculation filter. The sharp roll-off digital filter 13 performs filtering on the input digital audio signal and outputs it to the filter switching unit 18.

  The slow roll-off digital filter 12 and the sharp roll-off digital filter 13 are input with the same digital audio signal, are always processed in parallel, and are output with the same delay time by a delay device or the like.

In the present embodiment, the first digital mixer 14, the second digital mixer 15, and the comparison / determination unit 16 have a ratio of audio signal components that localize a sound image in the center of the digital audio signal is greater than a predetermined value. It is for determining whether or not. Here, depending on whether or not the ratio of the audio signal component included in “nC _L ” and “nC _R ” that locates the sound image in the center is larger than a predetermined value, the music piece is played by a small band performance. It is determined whether it is due to the performance of an orchestra or the like having a large organization.

  In the first digital mixer 14 and the second digital mixer 15, the same digital audio signal as that inputted to the slow roll-off digital filter 12 and the sharp roll-off digital filter 13 described above is always in parallel. Is input.

The first digital mixer 14 performs an operation “| L _T + R _T | = | L + nC _L + R + nC _R to obtain an absolute value of a value obtained by adding the left track audio signal“ L _T ”and the right track audio signal“ R _T ”. | "And outputs the calculation result to the comparison determination unit 16.

Second digital mixer. 15, calculation for obtaining the absolute value of the write track audio signal value obtained by subtracting _{"R T"} on the left track audio signal _{"L T" "| L T -R T | = |} L + nC L -R- nC _R | ”and outputs the calculation result to the comparison determination unit 16.

Here, the calculation performed by the first digital mixer 14 and the second digital mixer 15 will be described. As described above, the digital audio signals input to the digital audio signal processing apparatus 10 of the present embodiment are the left track audio signal “L _T ” and the right track audio signal “R _T ”. The ratio of the left track audio signal “L _T ” and the right track audio signal “R _T ” with respect to “| L _T + R _T |” and each audio signal component “L” with respect to the digital audio signal input to the digital audio signal processing apparatus 10 ”,“ R ”,“ C ”(“ nC _L ”and“ nC _R ”) do not change. That is, the ratio of the audio signal component to be localized at the center in “| L _T + R _T |” and the ratio of the audio signal component to be localized at the center in the digital audio signal input to the digital audio signal processing apparatus 10 are the same. is there.

When “| L _T −R _T |” is calculated, “L + nC _L −R−nC _R ” is obtained. Here, “−R” is the reverse phase of “R”, and “−nC _R ” is the reverse phase of “nC _R ”. As described above, in order to localize the sound image between “L” and “R”, “nC _L ” and “ _R ” are obtained by assigning the center channel audio signal “C” to each of “L” and “R”. nC _R ”. Accordingly, when “−nC _R ” having an antiphase with respect to “nC _L ” is calculated, the audio signal component localized between “L” and “R” is canceled by interference, and “nC _L ”, “nC _R ” ”Is reduced. That is, when “| L _T −R _T |” is calculated, the ratio of the audio signal component to be localized at the center in the digital audio signal input to the digital audio signal processing apparatus 10 is reduced. When “nC _L ” and “nC _R ” have many components of the same sound source / in-phase, there is a large decrease in components due to anti-phase interference. In addition, when “nC _L ” and “nC _R ” have few components of the same sound source / in-phase, there is little decrease in components due to anti-phase interference.

Therefore, “| L _T + R _T |” calculated by the first digital mixer 14 and the second digital mixer 15 and “| L _T −R _T |” are set in the center of the input digital audio signal. It is possible to determine the proportion of the audio signal component that localizes the sound image.

  In FIG. 1, the comparison / determination unit 16 localizes a sound image in the center of the input digital audio signal based on the value output from the first digital mixer 14 and the value output from the second digital mixer 15. It is determined whether the ratio of the audio signal component to be performed is greater than a predetermined value, and the determination result is output to the HOLD unit 17. It is assumed that this predetermined value is stored in a storage unit (not shown) or the like inside the comparison determination unit 16. Note that the comparison determination unit 16 outputs a result with the same delay time as the outputs of the slow roll-off digital filter 12 and the sharp roll-off digital filter 13 described above, using a delay unit or the like.

Here, the comparison / determination unit 16 stores a condition as shown in FIG. 2 in a storage unit (not shown) or the like, and localizes the sound image in the center of the input digital audio signal based on the condition. It is determined whether the ratio of the audio signal component is larger than a predetermined value. In the example of FIG. 2, the determination condition 30 of the comparison determination unit 16, whether or not the ratio of sound image localization at the center in the condition is larger than the reference value 31, the digital filter 32 that switches according to the condition, and the like are stored. When the value output from the first digital mixer is smaller than the product of the predetermined coefficient “X” and the value output from the second digital mixer (| L _T + R _T | ≦ X | L _T −R _T |), The ratio of the audio signal component that localizes the sound image in the center of the input digital audio signal is determined to be smaller than a predetermined value, and a signal for switching to the output from the slow roll-off digital filter 12 is output. When the value output from the first digital mixer is larger than the product of the predetermined coefficient “X” and the value output from the second digital mixer (| L _T + R _T |> X | L _T − R _T |), the ratio of the audio signal component that localizes the sound image in the center of the input digital audio signal is determined to be larger than a predetermined value, and a signal for switching to the output from the sharp roll-off digital filter 13 is output.

  The coefficient “X” is a coefficient that is a point of sound quality adjustment for switching between the output from the slow roll-off digital filter 12 and the output from the sharp roll-off digital filter 13 described above. This coefficient may be set in advance, or may be a value input by the viewer using the user interface 21 described later.

Here, an example of the coefficient “X” will be described. The audio signal input to the digital audio signal processing apparatus 10 includes only three sound sources “L”, “C”, and “R”, and “| L | = | C | = | R |”. If the condition is met, X = 3/2. More specifically, as described above, the left track audio signal can be expressed as “L _T = L + nC _L ”, and the right track audio signal can be expressed as “R _T = R + nC _R ”. From this, absolute values “| L _T + R _T |” and “| L _T −R _T |” are obtained as follows.

| L _T + R _T | = L + nC _L + R + nC _R
| L _T −R _T | = L + nC _L − (R + nC _R )
Here, since “| L | = | C | = | R |” is satisfied, the left channel audio signal “L” and the right channel audio signal “R” are set to 1 (L = R = 1), and “nC _L ”And“ nC _R ”where the coefficient“ n ”is 0.5, the result is as follows.

| L _T + R _T | = 1 × L + 0.5 × C _L + 1 × R + 0.5 × C _R
| L _T −R _T | = 1 × L + 0.5 × C _L − (1 × R + 0.5 × C _R )
In “| L _T + R _T |”, “C _L ” and “C _R ” are the same sound source / in-phase, and are added to be “| L _T + R _T | = 3”. In “| L _T −R _T |”, “C _L ” and “C _R ” are subtracted because they are in the same sound source / in-phase, and the components “L” and “−R” remain, so the sound pressure remains. The level becomes “| L _T −R _T | = 2”. As a result, the following holds.

| L _T + R _T | = 3/2 | L _T −R _T |
As described above, in general, in the case of music composed of a small band mainly composed of vocals, since the vocals are localized at the center position, the left track audio signal “L _T ” and the right track audio signal “R _T ”. Are evenly included in the voice component of vocals. The center channel audio signals “C” (“nC _L ” and “nC _R ”) included in the “L _T ” and “R _T ” track audio signals are the same sound source / in-phase sound, and “L _T ” and “R R”. _There is almost no phase shift from the _T "track audio signal. “L”, “R”, “C” Three sound sources are downmixed into a left track audio signal and a right track audio signal as a reference, and the ratio of the components that localize the sound image at the center is high, that is, “| L _{If “T} + R _T |> 3/2 | L _T− R _T |”, the music can be determined to be a performance by a small band or the like. When the ratio of the component that localizes the sound image at the center is low, that is, when “| L _T + R _T | ≦ 3/2 | L _T −R _T |”, the music is a large orchestra with a plurality of sound sources. Can be judged as a performance. Also, when the recording space is wide, even if the same sound source is included in “L” and “R”, a phase shift occurs. Therefore, “| L _T + R _T | ≦ 3/2 | L _T −R _T | ".

  In FIG. 1, a HOLD unit 17 receives information indicating a determination result output from the comparison determination unit 16, holds the information for a predetermined time, and outputs information indicating the latest determination result after a predetermined time. . In the present embodiment, it is assumed that the HOLD unit 17 holds a signal for switching the output of the filter by turning on or off a flag, for example. The time for holding the signal is, for example, 4 or 5 minutes corresponding to one music piece. This time may be determined in advance, or may be set by the viewer using a user interface 21 described later. For example, the HOLD unit 17 outputs a signal for switching the filter output, starts measuring time by a timer (not shown) provided therein, and passes a predetermined time stored in a storage unit or the like (not shown). Based on the information indicating the latest determination result, a signal for switching the filter output is output. Further, the holding of a signal for switching the output of the filter may be started or the holding of the signal may be canceled by a signal from the microcomputer 20 described later.

  As described above, the audio signal output processing device 10 according to the present embodiment determines whether or not the ratio of the sound image localization component at the center is equal to or greater than a predetermined value, and switches the filter output according to the determination result. Accordingly, in the case of an audio signal in which the output of the component that localizes the sound image changes frequently, the filter output may be frequently switched. For example, in the case of an audio signal of a performance by a large orchestra, etc., and a music with a melody where the sound image is localized in the center due to performance by a solo part, etc., the output level of the audio signal of the component that localizes the sound image at the center increases, There is a possibility that the sound image, the spread, etc. are frequently switched in one song. By holding the signal by the HOLD unit 17 described above, it is possible to reduce the possibility that the sound image and the spread feeling are frequently switched in one song.

  Based on the information output from the HOLD unit 17, the filter switching unit 18 switches the outputs of the slow roll-off digital filter 12 and the sharp roll-off digital filter 13 and outputs them to the output unit 19. In the present embodiment, for example, when a signal indicating that the component ratio of sound image localization is larger than a predetermined value is input at the center by turning on or off the flag, the output from the sharp roll-off digital filter 13 is output to the output unit 19. Shall be output. Further, for example, when a signal indicating that the ratio of the component that localizes the sound image is smaller than a predetermined value is input at the center by turning on or off the flag, the output from the slow roll-off digital filter 13 is output to the output unit 19. Shall.

  The user interface 21 is an interface for the viewer of the audio signal output device 10 to set up the device. In the present embodiment, a switching selection button for selecting whether the above-described filter switching is to be performed automatically or manually, and the filter output is the slow roll-off digital filter 12 or the sharp roll-off digital filter 13. A filter selection button for selecting the sound, a button for inputting a value for determining the ratio of the audio signal component having the sound image localization at the center by the comparison / determination unit 16, a time for holding the signal by the HOLD unit 17, and the like. It shall be. These buttons may be realized by a combination of a plurality of buttons and a dial.

  The microcomputer 20 controls the audio signal output device 10. In the present embodiment, the microcomputer 20 outputs a signal requesting determination as to whether or not the ratio of the audio signal component to be localized at the center is larger than a predetermined value, and the audio signal output device 10 It is assumed that processing for applying various settings input by the viewer using a user interface 21 described later is performed.

  A process in which the microcomputer 20 outputs a signal requesting the above-described comparison determination will be described. If the filter is switched in the middle of a song, the sound image or the like changes in the middle of the song, which may cause a sense of discomfort during viewing. Therefore, in the present embodiment, when the output level of the audio signal is sufficiently low including silence, or when the music starts, a signal requesting a comparison determination serving as a trigger for switching the filter is output.

  An example of detecting when the signal level of the digital audio signal is sufficiently small will be described. The microcomputer 20 stores in the storage unit (not shown) a threshold that prevents the viewer from hearing changes in the sound image. This threshold value may be set in advance, or may be set by a viewer or the like using the user interface 21. The microcomputer 20 receives the same digital audio signal as the digital audio signal input to the slow roll-off characteristic digital filter 12 and the sharp roll-off characteristic digital filter 13. When the microcomputer 20 compares the signal level of the digital audio signal sequentially input with the threshold value and detects that the signal level is lower than the threshold value, the microcomputer 20 determines that the signal level is sufficiently low and outputs a signal for which a comparison determination is requested. Output.

  An example of detecting when music starts will be described. In general, information relating to a digital audio signal is input to a medium such as a CD that stores the digital audio signal in association with the digital audio signal. The information relating to the digital audio signal is, for example, the track number, sampling frequency, number of bits, number of channels, etc. of the audio signal. Usually, since the sampling frequency and the number of channels are determined by the track (music) or the medium, it can be estimated that the track or the medium has changed due to a change in the sampling frequency and the number of channels.

  The microcomputer 20 receives the same signal as the digital audio signal input to the input unit 11 and information related to the digital audio signal stored in a medium such as a CD storing the signal. Information regarding the digital audio signal is input from a medium such as a CD via a digital interface (not shown). The microcomputer 20 extracts information such as a track number, a sampling frequency, and the number of channels from the input data, and stores the information in a storage unit (not shown) for a predetermined time. Next, the track number, sampling frequency, number of channels, etc. that are sequentially input are compared with the stored track number, sampling frequency, number of channels, etc., and it is determined whether any or more of those information has changed. Thus, it is detected that the track or the medium has changed. Also, when track number, sampling frequency, number of channels, etc. are not stored in the storage unit, that is, when track number, sampling frequency, number of channels, etc. are input only after the medium such as CD is changed, etc. A signal requesting determination may be output.

  When the microcomputer 20 detects that the output level is sufficiently low or the start of music as described above, the microcomputer 20 clears a signal for switching the filter held by the HOLD unit 17 by outputting a signal to the HOLD unit 17 or the like. Further, the microcomputer 20 outputs a signal requesting the comparison determination to the comparison determination unit 16. When the comparison determination unit 16 receives a signal requesting comparison determination, the comparison determination unit 16 performs the above-described comparison determination on the latest digital audio signal when the request signal is received.

  This makes it difficult for the viewer to hear the change in the sound image that occurs when the filter is switched, and makes the filter switching inconspicuous.

  A process in which the microcomputer 20 applies various settings input by the viewer of the audio signal output apparatus 10 using a user interface 21 described later will be described. The viewer uses the user interface 21 to input settings for the audio signal output device 10. As an input setting, for example, when the filter output is switched automatically or manually, or when the filter output is switched manually, the output from the slow roll-off type digital filter 12 or the sharp roll-off type digital filter 13 is used. Or the value (X) for the comparison determination unit 16 to perform the above-described comparison determination, the time for the HOLD unit 17 to hold the signal, and the like.

  For example, when the filter output is switched manually, the microcomputer 20 outputs a signal for switching to the filter selected by the viewer to the HOLD unit 17. The HOLD unit 17 outputs a signal for switching the filter according to the signal input from the microcomputer 20. At this time, the time for holding the signal for switching the filter by the HOLD unit 17 may be such that the filter is not switched until the setting is input again due to no time setting or the like. Also good. Furthermore, as described above, the microcomputer 20 may detect the change of the track or the medium, and may change the filter switching to the automatic switching according to the comparison determination request from the microcomputer 20.

  For example, when the comparison determination unit 16 sets a value (X) for the above comparison determination, the HOLD unit 17 sets a time for holding the signal, etc., the microcomputer 20 compares the information input to the viewer with the comparison determination unit 16. , HOLD unit 17 and the like. Each of the comparison determination unit 16, the HOLD unit 17, and the like performs processing such as replacing the input value with a value already stored in the storage unit or the like.

  An operation in which the input digital audio signal is processed and output by the digital audio signal processing apparatus 10 will be described. The audio signal is input from the input unit 11. The input audio signal is input to the slow roll-off digital filter 12, the sharp roll-off digital filter 13, the first digital mixer 14, the second digital mixer 15, and the microcomputer 20.

  The microcomputer 20 determines that the signal level is sufficiently low or the track or medium has changed (begins) based on the change in the number of channels, the sampling frequency, the output value of the audio signal, and the like. A signal requesting determination as to whether or not the ratio of the audio signal component of the sound image to be output is greater than a predetermined value is output.

  The slow roll-off type digital filter 12 performs filtering with a filter having a linear phase characteristic and outputs the result. The sharp roll-off digital filter 13 performs filter processing with a filter having a characteristic that the level sharply decreases at the cut-off frequency, and outputs the result. The slow roll-off digital filter 12 and the sharp roll-off digital filter 13 always perform parallel processing and output with the same delay time.

When the first digital mixer 14, the second digital mixer 15, and the comparison determination unit 16 receive a signal requesting determination from the microcomputer 20, the audio signal component of the sound image localized at the center in the input audio signal It is determined whether or not the ratio is greater than a predetermined value. Specifically, the first digital mixer 14 calculates “| L _T + R _T |” for the input audio signal and outputs the result. The second digital mixer 15 calculates “| L _T −R _T |” for the input audio signal and outputs the result.

When the comparison determination unit 16 receives the comparison request signal output from the microcomputer 20, the latest “| L _T + R _T |” value and “| L _T −R _T |” value at the time when the signal is received. Thus, it is determined whether or not the ratio of the audio signal component of the sound image localized at the center is larger than a predetermined value. When “| L _T + R _T | ≦ X | L _T −R _T |”, the comparison determination unit 16 determines that the ratio of the audio signal component of the sound image localized at the center is smaller than a predetermined value. When “| L _T + R _T |> X | L _T −R _T |”, it is determined that the ratio of the audio signal component of the sound image localized at the center is larger than a predetermined value. The comparison determination unit 16 outputs the determined result to the HOLD unit 17.

  The HOLD unit 17 holds a signal for switching the filter output based on the information indicating the comparison determination result output from the comparison determination unit 16. Here, the HOLD unit 17 receives information indicating the comparison determination result sequentially from the comparison determination unit 16. A signal for switching the filter output based on the latest information is output after a predetermined time since the signal for switching the filter output based on the information is output last time. When the signal from the microcomputer 20 is received, the signal for switching the filter output already held is cleared, and the signal for switching the filter output based on the information indicating the new comparison determination result transmitted from the comparison determination unit 16 is generated. Output.

  The filter switching unit 18 switches the output from the filter in accordance with the output from the HOLD unit 17. Here, when the ratio of the audio signal component of the sound image localized at the center is smaller than a predetermined value, the output is switched to the output from the slow roll-off digital filter, and the audio signal data output from the filter is output to the output unit 19 To do. When the ratio of the audio signal component of the sound image localized at the center is larger than a predetermined value, the output is switched to the output from the sharp roll-off digital filter, and the audio signal data output from the filter is output to the output unit 19.

  The above-described digital audio signal processing apparatus is provided in, for example, a DVD (Digital Versatile Disk) player, an AV (Audio Visual) amplifier, or the like. When provided in a DVD player, an AV amplifier, or the like, for example, data output from a signal processing circuit such as a decoder that decodes digital data is processed by the above-described digital audio signal processing apparatus, and the data processed by the apparatus is processed. Is D / A converted (digital / analog converter) and output to an output terminal or the like. When output as digital data, it is output to an output terminal or the like without being D / A converted.

  In the above-described embodiment, the example of the stereo reproduction system with two channels output has been described. However, the reproduction system is not limited to this, and for example, the 5.1 channel digital audio signal reproduction system may be used. Applicable. Usually, 5.1 channel digital audio signals include left channel audio signal “L”, right channel audio signal “R”, surround left channel audio signal “SL”, surround right channel audio signal “SR”, center channel audio. The signal “C” and the audio signal “LFE” of the bass dedicated channel are included. In general, in 5.1ch, a left channel audio signal “L”, a right channel audio signal “R”, and a center channel audio signal “C” are each output by three speakers installed in front of the viewing position. . The surround left channel audio signal “SL” and the surround right channel audio signal “SR” are each output by two speakers installed behind the viewing position. The audio signal “LFE” of the bass dedicated channel is output by a bass dedicated output device such as a woofer.

  When the filtering process by the digital audio signal processing apparatus described above is applied to a 5.1ch digital audio signal, for example, the left channel audio signal “L”, the right channel audio signal “R”, the surround left channel audio signal “SL”, and Each combination of the surround light channel audio signal “SR”, the center channel audio signal “C”, and the audio signal “LFE” of the bass dedicated channel is processed by one digital audio signal processing device. That is, three digital audio signal processing devices are applied to a 5.1ch digital audio signal.

When the digital audio signal processing apparatus is applied to the 5.1 channel digital audio signal reproduction method, the apparatus is not necessarily applied to all the combinations of the digital audio signals described above. For example, the left channel audio signal “L” is used. Only the combination of the left channel audio signal “R”, the left channel audio signal “L”, the right channel audio signal “R”, the surround left channel audio signal “SL”, and the surround right channel audio signal “SR”. But you can.
Second Embodiment
Next, a second embodiment will be described. In the second embodiment, the microcomputer 20 controls the operations of the first digital mixer 14, the second digital mixer 15, and the comparison determination unit 16 of the first embodiment described above. In the following description, components having the same configuration and operation as those of the first embodiment described above are given the same reference numerals and description thereof is omitted, and only different configurations and operations will be described in detail.

  FIG. 3 shows an example of the digital audio signal processing apparatus 10 of the second embodiment. In FIG. 3, the digital audio signal processing apparatus 10 includes an input unit 11, a slow roll-off type digital filter 12, a sharp roll-off type digital filter 13, a first digital mixer 14, a second digital mixer 15, and a comparison determination unit 16. , A HOLD unit 17, a filter switching unit 18, an output unit 19, a microcomputer 20, a user interface 21 and the like. The microcomputer 20 and the user interface 21 may be provided in the digital audio signal processing apparatus 10 or may be realized by using part or all of the functions of other apparatuses in the digital audio signal processing apparatus 10. Good.

  The microcomputer 20 receives the same digital audio signal as that input to the digital audio signal processing apparatus 10 and information related to the audio signal. The microcomputer 20 includes an MPU 201, a memory 202, a storage unit 203, and the like. The MPU 201 implements a switching control unit 211, a stop instruction unit 212, a registration unit 213, and the like by executing a program loaded in the memory 202.

  The storage unit 203 has one or more sets of areas for storing information relating to digital audio signals and areas for storing information indicating digital filters corresponding to information relating to the respective digital audio signals. In these areas, information related to the digital audio signal and information indicating the digital filter are stored by an operation described later.

  The switching control unit 211 searches the storage unit 203 for information that matches the information related to the input digital audio signal from the area for storing the information related to the digital audio signal. The information indicating the digital filter is read from the area corresponding to the area where the digital filter is stored, and the information indicating the read digital filter is output, thereby causing the filter switching unit 18 to switch the digital filter output. The stop instruction unit 212 stops the operations of the first digital mixer 14, the second digital mixer 15, and the comparison determination unit 16 when the switching control unit 211 outputs information indicating a digital filter. The registration unit 213 stores information related to the digital audio signal and the digital filter applied when the audio signal is input in the storage unit 203 in association with each other.

  Here, the information related to the digital audio signal is TOC (Table of Contents) information stored in a part of a medium such as a CD or added to the digital audio signal. The TOC information is information such as text information such as the total number of tracks stored in one medium, the track number of each song, the sampling frequency, the number of bits, the number of channels, the performance time, and the song name.

  Here, FIG. 4 shows an example of information stored in the storage unit 203 that associates the TOC information with the digital filter. In FIG. 4, the table 231 stores TOC information 2311 and a digital filter 2312 in association with each other. The TOC information 2311 is TOC information input to the microcomputer 20, and includes, for example, the total number of tracks stored in the medium, the track number of each song, the sampling frequency, the number of bits, the number of channels, the performance time, text information, and the like. All or part of the TOE information. The digital filter 2312 is information indicating the digital filter selected by the filter switching unit 18 when the corresponding TOC information is input. Information stored in the table 231 is acquired and stored by an operation described later.

  Input unit 11, slow roll-off type digital filter 12, sharp roll-off type digital filter 13, first digital mixer 14, second digital mixer 15, comparison judgment unit 16, HOLD unit 17, filter switching unit 18, output unit 19 and the user interface 21 are the same as those in the first embodiment described above except for the operations described later, and thus the description thereof is omitted.

  Next, an operation example of the second embodiment will be described. An example of the operation of the microcomputer 20 will be described with reference to FIG.

  The digital audio signal is input from the input unit 11. The input digital audio signal is input to the slow roll-off digital filter 12, the sharp roll-off digital filter 13, the first digital mixer 14, and the second digital mixer 15. The microcomputer 20 receives the same audio signal as the digital audio signal input to the input unit 11 and the TOC information of the digital audio signal.

  If it is determined that the signal level is sufficiently low or the track or medium has changed (beginning) due to the change in the number of channels, sampling frequency, audio signal output value, etc., the switching control unit 211 of the microcomputer 20 A TOC signal of a digital audio signal input in the past is read from a specific area (S501), and the same information as the TOC information input this time is included in the TOC signal of the digital audio signal input in the past. (S502). Here, the switching control unit 211 refers to the TOC information 2311 of the table 231 stored in the storage unit 203 and determines whether a part or all of the input TOC information is included in the TOC information 2311. .

  As a result of the determination in S502, when the corresponding TOC information is not included, the switching control unit 211 instructs the registration unit 213 to register the TOC information. Further, the switching control unit 211 outputs a comparison request signal requesting the comparison determination unit 16 to determine whether or not the ratio of the audio signal component of the sound image localized at the center is larger than a predetermined value, and the HOLD unit 17. In addition, a signal instructing clearing of the already held signal is output.

  On the other hand, the slow roll-off type digital filter 12 performs a filtering process with a filter having a linear phase characteristic and outputs it. The sharp roll-off digital filter 13 performs filter processing with a filter having a characteristic that the level sharply decreases at the cut-off frequency, and outputs the result. The slow roll-off digital filter 12 and the sharp roll-off digital filter 13 always perform parallel processing and output with the same delay time. This operation is the same as in the first embodiment described above.

  When the first digital mixer 14, the second digital mixer 15, and the comparison determination unit 16 receive a signal requesting determination from the microcomputer 20, the audio signal component of the sound image localized at the center in the input audio signal It is determined whether or not the ratio is greater than a predetermined value. Since this operation example is the same as that of the first embodiment described above, a description thereof will be omitted. The comparison determination unit 16 outputs the determined result to the HOLD unit 17.

  Here, when the operations of the first digital mixer 14, the second digital mixer 15, and the comparison determination unit 16 are stopped by the operation of the stop instruction unit 212 described later, the switching control unit 211 first After outputting a signal for operating each of the first digital mixer 14, the second digital mixer 15, and the comparison determination unit 16, a comparison request signal is output to the comparison determination unit 16 and the HOLD unit 17 as described above. A signal for instructing the clearing of the already held signal is output. In order to determine whether or not the operations of the first digital mixer 14, the second digital mixer 15, and the comparison determination unit 16 are stopped, for example, the switching control unit 211 sends a stop instruction unit 212 to the stop instruction unit 212 as described later. After the instruction, the flag indicating whether or not the operations of the first digital mixer 14, the second digital mixer 15, and the comparison determination unit 16 are stopped is changed. The switching control unit 211 refers to the flag and determines whether the operations of the first digital mixer 14, the second digital mixer 15, and the comparison determination unit 16 are stopped.

  When the signal from the microcomputer 20 is input, the HOLD unit 17 clears the signal for switching the filter output that is already held, and performs filtering based on the information indicating the new comparison determination result transmitted from the comparison determination unit 16. A signal for switching the output is output to the filter switching unit 18 and the microcomputer 20, and the signal is held for a predetermined time. The HOLD unit 17 outputs a signal for switching the filter output based on the latest input information after a predetermined time since the signal for switching the filter output based on the input information was previously output.

  On the other hand, the registration unit 213 of the microcomputer 20 stores the input TOC information and the information indicating the digital filter indicated by the information input from the HOLD unit 17 in association with each other in the storage unit 203 (S503). Specifically, for example, the registration unit 213 stores all or part of the input TOC information in the TOC information 2311 of the table 231, and information input from the HOLD unit 17 to the digital filter 2312 of the table 231. Information indicating the digital filter shown in FIG. In the present embodiment, the registration unit 213, when a signal indicating that the component ratio of sound image localization is larger than a predetermined value is input at the center, for example, by turning on or off a flag, indicates information indicating a sharp roll-off digital filter Is stored in the digital filter 2312 of the table 231. Further, when a signal indicating that the ratio of the component that localizes the sound image is smaller than a predetermined value is input to the center due to, for example, turning on or off the flag, the registration unit 213 stores information indicating the slow roll-off type digital filter in a table. It stores in the digital filter 2312 of H.231.

  The TOC information 2311 in the table 231 may be for each medium or for each piece of music. In the case of each medium, the TOC information 2311 stores, for example, sampling frequency, the number of bits, the number of channels, the total number of tracks, text information of the title name of the medium, and the like. Further, in the case of each piece of music, the TOC information 2311 includes, for example, information about each medium such as sampling frequency, number of bits, number of channels, total number of tracks, medium title name text information, and the track number of the music piece. In addition, text information such as a song name is stored.

  The filter switching unit 18 switches the output from the filter in accordance with the output from the HOLD unit 17.

  If the input TOC information is included as a result of the determination in S502, the switching control unit 211 reads out information indicating a digital filter corresponding to the input TOC information from the storage unit 203, and stores the information in the HOLD unit 17. A signal for instructing clearing of the already held signal and information indicating the read digital filter are output (S504). Specifically, for example, the switching control unit 211 reads out the digital filter 2312 associated with the TOC information 2311 that matches all or a part of the input TOC information from the table 231, and indicates the digital filter Is output to the HOLD unit 17.

  The HOLD 17 outputs a signal for switching to the digital filter indicated by the information input from the microcomputer 20 to the filter switching unit 18 as described above.

  On the other hand, the stop instruction unit 212 of the microcomputer 20 stops the operations of the first digital mixer 14, the second digital mixer 15, and the comparison determination unit 16 (S505). Specifically, for example, when the input of TOC information is included as a result of the determination of S502 by the switching control unit 211, the stop instruction unit 212 includes the first digital mixer 14, the second digital mixer 15, A signal for stopping each operation is output to the comparison determination unit 16. This output may be after the operation of S504, that is, after the operation in which the switching control unit 211 outputs information indicating the filter to the HOLD unit 17, or may be earlier.

  When each of the first digital mixer 14, the second digital mixer 15, and the comparison determination unit 16 receives a signal from the microcomputer 20, the operation is stopped according to the signal.

  As described above, when the same digital audio signal is input in the past, the output is switched to the output from the digital filter selected in the past, and the operations of the first digital mixer 14, the second digital mixer 15, and the comparison determination unit 16 are performed. Can be stopped. Since useless operations of the first digital mixer 14, the second digital mixer 15, and the comparison determination unit 16 can be stopped, power consumption can be reduced.

  When information indicating an instruction to switch the filter manually and information indicating a digital filter to be switched are input from the user interface 21 at an arbitrary processing stage of the operation illustrated in FIG. The HOLD unit 17 outputs a signal for clearing the already held signal and a signal for switching to the input digital filter. Further, the switching control unit 211 instructs the stop instruction unit 212 to stop the arithmetic device, and instructs the registration unit 213 to register the TOC information.

  In accordance with the instruction, the stop instruction unit 212 stops the operations of the first digital mixer 14, the second digital mixer 15, and the comparison determination unit 16 in the same manner as described above. Further, according to the instruction, the registration unit 213 converts the TOC information for each piece of music or each medium at that time point and information indicating the digital filter input from the user interface 21 into the TOC information 2311 and the digital information in the same manner as described above. The filter 2312 is stored in the table 231.

  On the other hand, the HOLD 17 outputs a signal for switching to the digital filter indicated by the information input from the microcomputer 20 to the filter switching unit 18 as described above.

  As described above, when information indicating a digital filter is input from the user interface 21 in accordance with the preference of the viewer, the first digital signal is switched to the output from the digital filter indicated by the input information. The operations of the mixer 14, the second digital mixer 15, and the comparison / determination unit 16 can be stopped. Since useless operations of the first digital mixer 14, the second digital mixer 15, and the comparison / determination unit 16 can be stopped, power consumption can be reduced even in the case of a digital audio signal input for the first time. Become.

  Further, as described above, when information indicating a digital filter is input from the user interface 21, the information indicating the input digital filter and the TOC information are associated with each other and stored in the storage unit 203. When the same digital audio signal is input next time, the viewer can view the output from the same digital filter as the previous one without using the user interface 21 to instruct the digital filter.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and includes design changes and the like within a scope not departing from the gist of the present invention.

  For example, when information indicating an instruction to manually switch a filter and information indicating a digital filter to be switched are input from the user interface and the same TOC information is already stored in the table, the registration unit has already stored the information. The information indicating the new digital filter may be overwritten on the information indicating the digital filter associated with the TOC information, and is stored separately in association with the current time obtained from the internal clock (not shown). May be.

  For example, when a plurality of pieces of TOC information that match the input TOC information are stored, the determination unit has the largest number of times of correspondence among the digital filters associated with the matching TOC information. Information indicating a digital filter may be output, or information indicating a digital filter associated with the current date and time may be output.

  Further, for example, the stop instructing unit may stop the operation of a digital filter other than the digital filter switched and output by the filter switching unit.

It is a figure which shows the structural example in one Embodiment of this invention. In the same embodiment, it is a figure which shows the example of the conditions which determine whether the ratio by which a sound image is localized to the center of a digital audio signal is larger than a reference value. In the same embodiment, it is a figure which shows the other structural example of a digital audio signal processing apparatus. In the embodiment, the information about the digital audio signal and the digital filter selected when the digital audio signal is input are stored in association with each other. FIG. 6 is a flowchart for explaining an operation example of a microcomputer in the embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10: Digital audio signal processing apparatus, 11 input part, 12: Slow roll-off type digital filter, 13: Sharp roll-off type digital filter, 14: 1st digital mixer, 15: 2nd digital mixer, 16: Comparison determination Part: 17: HOLD part, 18: filter switching part, 19: output part, 20: microcomputer, 21: user interface 21: judgment condition of comparison judgment means 16, 31: ratio of sound image localization in the center, 32: digital filter, 201 : MPU, 202: Memory, 203: Storage unit, 211: Switching control unit, 212: Stop instruction unit, 231: Registration unit, 231: Table, 2311: TOC information, 2312: Digital filter

Claims (9)

At least a digital audio signal output device to which a digital audio signal including an audio signal that localizes a sound image is input at the center,
A slow roll-off characteristic digital filter for filtering and outputting the digital audio signal;
A sharp roll-off characteristic digital filter for filtering and outputting the digital audio signal;
A comparison / determination means for outputting information indicating a result of comparison / determination whether or not a ratio of an audio signal component that localizes a sound image in the center of the digital audio signal is larger than a predetermined value;
According to the information indicating the result of the comparison determination, switching means for switching and outputting the output from the slow roll-off characteristic digital filter and the output from the sharp roll-off characteristic digital filter,
A digital audio signal output device comprising: The digital audio signal output device according to claim 1,
The switching means switches to the output from the sharp roll-off digital filter when information indicating that the ratio of the audio signal component for locating the sound image at the center is greater than a predetermined value is input, and the sound image at the center The digital audio signal output apparatus is characterized in that, when information indicating that the ratio of the audio signal component for localizing the signal is smaller than a predetermined value is input, the output is switched to the output from the slow roll-off characteristic digital filter. The digital audio signal output device according to claim 1 or 2,
Information indicating the result of the comparison determination is input from the comparison determination unit, and information indicating the latest comparison determination result is output after a predetermined time since the information indicating the result of the previous comparison determination is output to the switching unit. HOLD means for outputting
The switching means switches between an output from the slow roll-off characteristic digital filter and an output from the sharp roll-off characteristic digital filter based on information inputted from the HOLD means. . A digital audio signal output device according to any one of claims 1 to 3,
Request signal output means for outputting a request signal to the comparison determination means,
The digital audio signal output device according to claim 1, wherein when the request signal is received, the comparison / determination unit performs a comparative determination of a ratio of an audio signal component that localizes a sound image in the center of the digital audio signal. A digital audio signal output device to which a digital audio signal in which a center channel audio signal, a left channel audio signal, and a right channel audio signal are downmixed into a left track audio signal and a right track audio signal is input,
A slow roll-off characteristic digital filter for filtering and outputting the digital audio signal;
A sharp roll-off characteristic digital filter for filtering and outputting the digital audio signal;
A result of comparing and determining whether a ratio between a signal sum of the left track audio signal and the right track audio signal and a signal difference between the left track audio signal and the right track audio signal is larger than a predetermined value is shown. A comparison determination means for outputting information;
According to the information indicating the result of the comparison determination, switching means for switching and outputting the output from the slow roll-off characteristic digital filter and the output from the sharp roll-off characteristic digital filter,
A digital audio signal output device comprising: The digital audio signal output device according to claim 5,
The switching means is information indicating that a ratio of a signal sum between the left track audio signal and the right track audio signal and a signal difference between the left track audio signal and the right track audio signal is larger than a predetermined value. Is input to the output from the sharp roll-off characteristic digital filter, the signal sum of the left track audio signal and the right track audio signal, and the signal difference between the left track audio signal and the right track audio signal The digital audio signal output device is characterized in that when the information indicating that the ratio is less than a predetermined value is input, the output is switched to the output from the slow roll-off characteristic digital filter. The digital audio signal output device according to any one of claims 1 to 6,
The digital audio signal output device further receives information on the input digital audio signal,
Storage means for storing information relating to a digital audio signal and information indicating any one of the plurality of digital filters in association with each other;
When the storage means includes information related to the digital audio signal that matches the information related to the input digital audio signal, information indicating a digital filter associated with the information related to the digital audio signal is stored in the storage means. Switching control means for reading and outputting information indicating the digital filter to the switching means;
Stopping means for stopping the operation of the comparison determination means when the storage means includes information relating to the digital audio signal that matches the information relating to the input digital audio signal;
The digital audio signal output device, wherein the switching means switches to an output from a digital filter indicated by information output from the switching control means. The digital audio signal output device according to claim 7,
When the storage means does not include information on the digital audio signal that matches the information on the input digital audio signal, the information on the input digital audio signal and the digital filter whose output has been switched by the switching means The digital audio signal output device further comprises registration means for associating and storing the information indicating the information in the storage means. The digital audio signal output device according to claim 7 or 8,
An input means for inputting information indicating the slow roll-off characteristic digital filter or the sharp roll-off characteristic digital filter;
The stop means stops the operation of the comparison determination means,
The digital audio signal output apparatus characterized in that the switching means switches to an output from a digital filter indicated by information input to the input means.

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