JP2002118897A - False stereophonic device and audio amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a false stereophonic device capable of automatically turning on/off a function by determining whether an input signal is a stereophonic signal or a monaural signal. SOLUTION: A decision part 10 determines whether an input signal is a stereophonic signal or a monaural signal. The decision can be performed by determining the level of a differential signal obtained by subtracting a right(R) channel signal from a left(L) channel signal. When the input signal is the stereophonic signal, a switching part 12 is switched to the input terminal side to output the input signal directly as a through signal. When the input signal is the monaural signal, the switching part 12 is switched to the side of a filter part 11 and a false stereophonic signal converted from the input signal is outputted. The filter part 11 is constituted of a comb filter of two systems mutually shifting their filtering bands.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pseudo-stereo device for converting a monaural signal into a pseudo-stereo signal, and an audio amplifier incorporating the same.

[0002]

2. Description of the Related Art When a monaural signal is reproduced by a stereo apparatus, if the signal is reproduced as it is, the sound image is concentrated at the center and the sound field does not spread, so this signal is converted into a pseudo stereo signal and converted into a sound field. There is a pseudo-stereo device that gives a spacious look.

On the other hand, since a true stereo signal is a signal in which the localization of a plurality of sounds is different from each other and is originally spread over the sound field, if this signal is processed by a pseudo-stereo device, the localization of the original sound image is blurred. This has the opposite effect.

Conventionally, the user turns on the pseudo-stereo device when the audio source (input signal) is monaural, and turns off the pseudo-stereo device when the audio source is stereo. I was going.

[0005]

In an album or the like in which old songs are collected, stereo songs and monaural songs are mixed, and it is extremely troublesome for the user to operate a switch every time the song changes. It was something.

An object of the present invention is to provide a pseudo-stereo device capable of judging whether an input signal is a stereo signal or a monaural signal and automatically turning on / off a function, and an audio amplifier incorporating the pseudo-stereo device. With the goal.

[0007]

According to the present invention, there is provided a signal conversion means for converting a monaural signal into a pseudo stereo signal,
It determines whether the input signal is a stereo signal or a monaural signal. If the input signal is a stereo signal, the signal is output as it is as a through signal to the outside, and if the input signal is a monaural signal, the signal is output. And a control unit for converting the converted signal into a pseudo stereo signal by a signal conversion unit and outputting the converted signal as a pseudo stereo signal to the outside. The present invention is characterized in that the control means determines whether the signal is a stereo signal or a monaural signal based on a level difference between input signals of a plurality of channels. According to the present invention, when a stereo signal is input, it is output to a next-stage device as it is as a through signal, and when a monaural signal is input, it is converted into a pseudo-stereo signal to convert it to a next-stage device. Output to The control means determines whether the input signal is a stereo signal or a monaural signal, and performs the above switching. For the determination of the stereo signal / monaural signal, for example, a level difference between input signals of a plurality of channels is obtained, and when the difference is small (or almost nonexistent), it is determined that the signal is a monaural signal.
If this is greater than a certain level, it can be determined that the signal is a stereo signal. Thus, the pseudo stereo function can be automatically turned on / off according to the input signal without the user manually switching.

The present invention is characterized in that the control means normally outputs a through signal externally and outputs a pseudo stereo signal only when it is determined that the input signal is a monaural signal. Currently, most audio sources are stereo sources. Normally (by default), the through signal is output to the outside, so that the switching process is performed only when the source is a monaural source, and the stereo source can be output to the outside as it is. It will be easier.

The present invention is characterized in that the control means gradually switches the externally output signal from a through signal to a pseudo stereo signal. Further, the invention is characterized in that a display means for displaying the degree of the switching is provided. If no signal is input after the music starts, it cannot be determined whether the signal is a stereo signal or a monaural signal. Therefore, switching from a through signal to a pseudo-stereo signal or from a pseudo-stereo signal to a through signal occurs in the middle of a song. Therefore, according to the present invention, by performing this switching gradually, the switching can be performed without suddenly changing the sound field feeling and giving the listener an unnatural feeling. Also, by displaying the degree of this switching, that is, the degree of the pseudo-stereo effect,
It is possible for the user to know the operation state of how much the pseudo-stereo is being converted.

According to the present invention, there is provided delay means for delaying an input signal by a predetermined time, wherein the control means determines whether a signal before the delay means is a monaural signal or a stereo signal, and the signal conversion means comprises a delay means. Is converted into a pseudo-stereo signal. The control means determines whether the signal before being input to the delay means is a stereo signal or a monaural signal, and the signal conversion means converts the signal delayed by the delay means. It is possible to determine in advance whether the signal is a stereo signal or a monaural signal. That is, the control unit can pre-read the signal to the signal conversion unit. Thus, the switching of the processing is not delayed from the switching from the stereo signal to the monaural signal.

According to the present invention, when the control means determines that the input signal is a monaural signal, the control means immediately switches the externally output signal from a through signal to a pseudo stereo signal, and externally outputs a repeat cueing instruction signal. It is characterized by. The repeat cueing is an operation in which an audio source reproducing device such as a CD player reproduces the currently reproduced music again from the beginning. According to the present invention, even if it is determined that the music is a monaural signal (stereo signal) after the start of the music, a repeat cueing instruction signal for instructing this is output to the audio source reproducing apparatus. Pseudo stereo function on (off)
You can redo the playback.

[0012]

FIG. 1 is a block diagram of an audio amplifier according to an embodiment of the present invention. This amplifier has a digital input terminal DigitalIN and an analog input terminal AnalogIN. Both terminals (L /
R) Two-channel stereo signals can be input. The signal input from the analog input terminal AnalogIN is converted into a pseudo stereo DSP through the AD converter 1.
2 is input. Also, the digital input terminal Digita
The signal input from LIN is directly a DSP for pseudo stereo.
2 is input.

The pseudo stereo DSP 2 receives the input 2
If the channel signal is a true stereo signal, the signal is directly input to the effect (equalizing) DSP 3 as a through signal. Also, if the input signal is 2
In the case of a monaural signal having the same signal for both channels, this signal is converted to pseudo stereo and input to the effect DSP 3 as a pseudo stereo signal. An indicator 2b is connected to the pseudo-stereo DSP 2, and the pseudo-stereo DSP 2 is connected to the indicator 2b in accordance with the degree of the pseudo-stereo effect given to the input signal.
The lighting mode of b is controlled.

The effect DSP 3 performs equalization for adjusting the frequency spectrum of the input signal and performs effects such as hall reverberation. The stereo signal (including the pseudo stereo signal) to which the equalization and the effect have been applied is converted into an analog signal by the DA converter 4 and then input to the output amplifier 5. The analog signal amplified by the output amplifier 5 is input to the speaker 6,
The sound is output by the speaker 6.

In the audio amplifier having this configuration, the pseudo stereo DSP 2 automatically determines whether the input two-channel signal is a true stereo signal or a monaural signal. Then, in the case of an analog signal, this signal is converted into a pseudo stereo signal and then output to the next stage as a pseudo stereo signal.

FIG. 2 is a functional block diagram of the DSP 2 for pseudo stereo. In the pseudo-stereo DSP 2, each functional unit of the determination unit 10, the filter unit 11, and the switching unit 12 is configured by a microprogram. Judgment unit 10
Is a functional unit that determines whether the input two-channel signal is a true stereo signal or a monaural signal. Although the two-channel signal is represented by two signal lines in FIG. 1, the two-channel digital signal is actually processed in a time-division manner.

Referring to FIG. 3A, the determination process of the determination unit 10 will be described. The determination unit 10 calculates the addition signal Ls by adding the signals of the two channels, and calculates the absolute difference signal Ld by subtracting the signals of the two channels. Then, when the target signal is input when the addition signal Ls becomes equal to or more than the predetermined value, the level of the absolute difference signal Ld at that time is determined. If the level is equal to or higher than a predetermined threshold, the signal is determined to be a true stereo signal, and if the level is equal to or lower than the predetermined threshold, the signal is determined to be a monaural signal. In other words, if the signal is a stereo signal, the signals of both the left and right channels are recorded by different systems, so that the level difference (the difference absolute value signal L
d) is large, whereas in the case of a monaural signal, L / R
Since the signals of both channels are signals of exactly the same system, stereo / monaural determination is made based on the fact that the level difference (absolute difference signal Ld) is extremely small. The above determination operation is continued for a predetermined time (2 to 3 seconds) in order to ensure the determination. Then, the difference absolute value signal L
If d does not exceed the threshold at all or for a short time (1
If the difference exceeds only about (%), it is determined that the signal is a monaural signal. On the other hand, if the difference absolute value signal Ld exceeds the threshold value during most (about 90%) of the determination section, it is determined that the signal is a stereo signal.

When the determination unit 10 determines that the input two-channel audio signal is a stereo signal, it turns off the function of the filter unit 11 and sets the switching unit 12 to through. If it is determined that the input two-channel audio signal is a monaural signal, the filter unit 11
Is turned on, and the switching unit 12 is switched to the filter unit 11 side. That is, the signal output from the filter unit 11 is output to the next stage (effect DSP 3).

Next, the function of the filter unit 11 will be described with reference to FIGS. The filter section 11 is a comb filter of two systems in which the peaks of the pass frequency band are alternated as shown in FIG. 3B, and each corresponds to two L / R channels. A monaural signal is input to the two comb filters, the output of one filter is output as a signal of the L channel, and the output of the other filter is output as a signal of the R channel. A pseudo stereo effect can be obtained.

Here, when the input two-channel audio signal is originally a stereo signal, pseudo-stereo by the comb filter is unnecessary because the source signal itself has a sound field spread. Therefore,
If the input signal is a stereo signal, the determination unit 10 switches the switching unit 12 to the input terminal side (through),
The input audio signal is output to the next stage as a through signal as it is. On the other hand, when the input signal is a monaural signal, the determination unit 10 operates the filter unit 11 and switches the switching unit 12 to the filter unit 11 side (pseudo stereo), and outputs the pseudo stereo signal to the next stage.
In this switching, if the input terminal is instantaneously switched from the input terminal side to the filter unit 11 side, the change of the sound field becomes abrupt, discontinuous and unnatural, so that the switching unit 12 is continuously switched from the input terminal side to the filter unit 11 side. The switching is performed while mixing both signal components, and the mixing ratio is gradually switched from 100% on the input terminal side to 100% on the filter section 11 side. Thereby, the frequency characteristic (cutoff characteristic of the filter) of the signal output from the switching section 12 is
As shown in the figure, the sound becomes gradually deeper and sharper, and the pseudo-stereo effect gradually becomes stronger. This eliminates the unnatural feeling when switching from through to pseudo-stereo during the song. The determining unit 10 controls the lighting mode of the indicator 2b according to the degree of the pseudo stereo effect. The indicator 2b is, for example, a plurality of LEDs
In this case, the number of lit LEDs may be increased in accordance with the strength of the pseudo-stereo effect. Also,
When the indicator can change the emission color, the emission color may be changed between the through and the pseudo stereo, and the light may be emitted in an intermediate color according to the degree of the pseudo stereo.

In this embodiment, the input signal as it is and the signal filtered by the filter unit 11 are mixed, and the mixing ratio is gradually changed to continuously change the frequency characteristic as shown in FIG. The filter section 11 is configured by a filter section capable of changing the filtering characteristic as shown in FIG. 4 so that the switching section is configured as shown in FIG. It can be a simple switch, and the switching unit 12 can be eliminated.

When a plurality of music pieces are continuously input, the judgment section 10 judges whether each music piece is a stereo music piece or a monaural music piece, and determines through music / pseudo stereo music for each music piece. Switch. This function is effective, for example, when playing an album in which stereo songs and monaural songs are mixed.
Since most audio sources currently have stereo sources, the default setting at the start of music is set to stereo, and the pseudo-stereo function is turned on when it is determined that the audio source is an analog source at the start of music.

FIG. 5 is a flowchart showing the operation of the determination unit 10. This operation is performed at predetermined time intervals, and determines whether the song is a stereo song or a monaural song between input songs and at the start of the song, and determines whether the song is a stereo song or a monaural song. 12 illustrates an operation of controlling the control signal T.12. It is determined whether there is a current music piece by using a music piece flag (s1). If the inter-song flag is set, it is between songs, and if it is reset, the song is being played. If the inter-song flag is reset, the operation below s2 is executed,
If it is set, the operation of s10 or less is executed.

If the inter-song flag is reset,
Proceeding to s2, it is determined whether the currently input signal is a silent signal. In the case of digital input, silence is data of all 0s, but in the case of analog input, there is a level of a noise component. The threshold value for judging silence is appropriately determined in consideration of this. Further, the threshold value may be changed according to whether the input is digital or analog.

If the section is not a silent section, that is, while a song is being input, the length of the silent section is counted and a timer for judging whether the section is between songs is reset and the process returns (s3). If it is a silent section, the timer is counted up (s4). When the timer times out due to the count-up (s5), it is determined that the current time is between songs, the filter unit 11 and the switching unit 12 are reset for inputting a stereo signal (s6), and a song interval flag is set. (S7). The timer is set so that the time is up in about 3 seconds, and if there is a space of 4 seconds, it is possible to reliably determine that there is a music interval. If a space between songs is detected, the through setting of the default setting is returned to the next song, and a flag between songs indicating that there is a space between songs is set.

On the other hand, if it is determined in s1 that the music is between music pieces, it is determined in s10 whether the silent section has ended and the next music piece has started. If the song has not started, the program returns. When the music starts, the inter-music flag is reset (s11), and as shown in FIG. 3A, the music is a stereo music or a monaural music based on the addition signal Ls and the absolute difference signal Ld. It is determined whether the song is a song (s12). If the operation is determined to be stereo, the default setting may be left as it is, and the process returns. On the other hand, if it is determined in the above determination operation that the input signal is monaural, the filter unit 11 is operated and the switching unit 12 is gradually switched to the filter unit 11 side, so that it takes a few seconds to gradually shift to the pseudo stereo. (S14).

Thus, if the input audio signal of the music is monaural, it can be detected and automatically switched to pseudo stereo, and the person who is listening to make the transition gradually It does not make you feel uncomfortable.

If the determination unit 10 can output a playback control signal to an audio source playback device (such as a CD player), if the music is monaural, the function is changed to a pseudo stereo. In addition, it is also possible to instruct the audio source playback device to start the current song (repeat cueing) and to reproduce the song again. In this case, in s14 of the flowchart, the DSP is immediately switched to the pseudo-stereo, and the start of the music is instructed to the audio source reproducing device.

A buffer 13 is provided as shown in FIG. 6 so that the determination unit 10 can determine whether the signal is a stereo signal or a monaural signal before the signal is input to the filter unit 11 or the switching unit 12. It is also possible to keep.
In this DSP, the buffer 13 can buffer digital audio signals for 3 seconds by FIFO. Therefore, the input audio signal is input to the filter unit 11 and the switching unit 12 after being delayed by the buffer 13 for 3 seconds. At the beginning of a song, the determination unit 10 determines whether the song is a stereo song or a monaural song based on the input signal. This determination is made within 3 seconds of the beginning of the song. When it is determined that the music is a monaural music piece, the filter unit 11 and the switching unit 12 are instructed to immediately shift to the pseudo stereo. As a result, the signal of the song delayed by 3 seconds in the buffer 13 is output in pseudo stereo from the beginning of the song. The switching unit 12 may be a switch as shown in FIG.

In this configuration, the filter unit 11
However, by making the filtering characteristics flat and capable of switching the characteristics as shown in FIG.
The switching unit 12 can be omitted.

In this embodiment, the pseudo stereo function is constituted by the DSP, but it may be constituted by hardware. Further, in this embodiment, the pseudo stereo DSP is incorporated in a part of the audio amplifier. However, the pseudo stereo device may be constituted as a single unit, and a reproducing device such as a CD player and the audio amplifier are combined. May be configured as a device.

Also, in the above embodiment, it is determined whether the input signal is stereo or monaural, and the switching between the through signal and the pseudo stereo signal is automatically performed. In addition to this, as shown by the broken line in FIG. A changeover switch 2a may be provided so that the user can manually change over.

[0033]

As described above, according to the present invention, it is determined whether an input signal is a stereo signal or a monaural signal, and the pseudo stereo function is automatically turned on / off.
Even if the user does not switch the function on / off by a manual switch operation, a CD album in which a stereo source and a monaural source are mixed can be reproduced comfortably.

[Brief description of the drawings]

FIG. 1 is a block diagram of an audio amplifier according to an embodiment of the present invention.

FIG. 2 is a functional block diagram of a pseudo stereo DSP of an audio amplifier.

FIG. 3 is a diagram illustrating functions of a determination unit and a filter unit of the pseudo stereo DSP.

FIG. 4 is a diagram showing a change in the frequency characteristic of an output signal when a transition is made from through to pseudo-stereo.

FIG. 5 is a flowchart illustrating an operation of a determination unit.

FIG. 6 is a pseudo-stereo DS according to another embodiment of the present invention.
Functional block diagram of P

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... AD converter, 2 ... Pseudo stereo DSP, changeover switch 2a, 3 ... DSP for effect, 4 ... DA converter, 5 ... Output amplifier, 6 ... Speaker, 10 ... Judgment part, 11 ... Filter part, 12 ... Switch part , 13 ... buffer

Claims (8)

[Claims] A signal conversion unit for converting a monaural signal into a pseudo stereo signal; determining whether the input signal is a stereo signal or a monaural signal; Control means for externally outputting as a through signal as it is, and when the input signal is a monaural signal, converting the signal into a pseudo stereo signal by a signal conversion means, and externally outputting the converted signal as a pseudo stereo signal; and A pseudo-stereo device with,. 2. The pseudo-stereo device according to claim 1, wherein the control unit determines whether the signal is a stereo signal or a monaural signal based on a level difference between input signals of a plurality of channels. 3. The pseudo stereo according to claim 1, wherein the control means normally outputs a through signal externally and outputs a pseudo stereo signal only when the input signal is determined to be a monaural signal. apparatus. 4. The pseudo-stereo apparatus according to claim 1, wherein said control means gradually switches the externally output signal from a through signal to a pseudo-stereo signal. 5. The pseudo-stereo device according to claim 4, further comprising display means for displaying the degree of the switching. 6. A delay unit for delaying an input signal by a predetermined time, wherein the control unit determines whether a signal before the delay unit is a monaural signal or a stereo signal, and the signal conversion unit outputs the signal from the delay unit. The pseudo-stereo device according to claim 1, 2 or 3, wherein the converted signal is converted into a pseudo-stereo signal. 7. When the control means determines that the input signal is a monaural signal, the control means immediately switches the externally output signal from a through signal to a pseudo-stereo signal and externally outputs a repeat cueing instruction signal. , Claim 2
Alternatively, the pseudo stereo device according to claim 3. 8. An audio amplifier incorporating the pseudo-stereo device according to claim 1 in a front end.