JPH0290900A - Pseudo stereo system - Google Patents

Abstract

PURPOSE:To transmit a monaural sound signal as if a stereo sound is emitted by delaying the sum signal of a right a left sound signals, forming a delay sum signal, and obtaining the sound signals of the right and left channels from the sum and difference between the sum signal and the delay sum signal. CONSTITUTION:In a monaural converting circuit MSK 1, a delay circuit 5 to delay a sum signal L+R outputted from a matrix circuit 1 is composed of a filter at eight stages using an arithmetic amplifier, and its output signal D is supplied to a matrix circuit 6. The matrix circuit 6 adds the sum signal L+R and the signal D, outputs them as a first addition signal La, adds the sum signal L+R and the signal obtained by inverting the signal D (the signal D is subtracted from the sum signal L+R), and outputs them as a second addition signal Ra. Here, the frequency component of the sum signal L+R and that of the signal D are different. Thus, by supplying the signals La and Ra obtained from the sum and difference of these signals to right and left speakers, the sound like a stereo broadcast (pseudo stereo sound) can be emitted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a pseudo-stereo system that enables monaural audio signals to be produced with a sound similar to stereo broadcasting.

``Prior art'' In audio stereo broadcasting, a matrix is used to convert the audio signals of both left and right channels into a sum signal and a difference signal and transmit them in order to enable common use with monaural broadcasting and reception by monaural receivers. method is used. When receiving this audio stereo broadcast, the receiving side uses a matrix circuit to restore the left and right channel audio signals from the sum signal and difference signal.

"Problem to be Solved by the Invention" By the way, not all stereo broadcast programs are stereo broadcasts, and monaural records or monaural recorded sound sources may be used.

In the case of such a monaural sound source, even if it is broadcast in stereo and received using a stereo receiver, the left audio signal and right audio signal will be restored as the same audio signal, so it will be perceived as monaural audio. be done. As a result, the sound lacks a sense of realism and vividness compared to stereo sound.

This invention was made in view of the above-mentioned circumstances, and aims to provide a pseudo-stereo system that makes it possible to generate sound that can be recognized as similar to stereo broadcasting when receiving monaural broadcasting. The purpose is

"Means for Solving the Problem" The first invention is to form a sum signal by adding a left audio signal and a right audio signal, to form a delayed sum signal by delaying this sum signal, and to form a delayed sum signal by delaying this sum signal. A first addition signal is formed by adding the signal and the sum signal, and a second addition signal is formed by adding the sum signal and an inverted delayed sum signal obtained by inverting the polarity of the delayed sum signal. , one of the first and second added signals is output as a right channel audio signal, and the other is output as a left channel audio signal.

The second invention calculates the sum and difference of the left audio signal and the right audio signal to form a sum signal and a difference signal, respectively, and forms a delayed sum signal by delaying this sum signal, and combines this delayed sum signal with the A first sum signal is formed by adding the sum signal, and a second sum signal is formed by adding the sum signal and an inverted delayed sum signal obtained by inverting the polarity of the delayed sum signal. The present invention is characterized in that either a set of the first and second added signals or the left audio signal and the right audio signal is selected based on the level of the difference signal and output as left and right channel audio signals.

"Operation" According to the present invention, a sum signal, which is the sum of left and right audio signals, is delayed to form a delayed sum signal, and left and right channel audio signals are obtained from the sum and difference of the sum signal and the delayed sum signal. As a result, the frequency components of the left and right channel audio signals are different, making it possible to produce a monaural audio signal as if it were a stereo sound.

"Embodiments" Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a monaural-stereo conversion circuit MSKI to which a pseudo-stereo system is applied according to a first embodiment of the present invention.
FIG. 2 is a block diagram showing the configuration of FIG.

In this figure, TI is an input terminal to which the left audio signal R is applied, the second is an input terminal to which the right audio signal R is applied, and l is the left audio signal and right audio signal supplied from the input terminals TI and T2. The sum signal R due to the sum of R and the difference signal L due to the difference
-R is a matrix circuit that generates R. 2 is a diode that rectifies the difference signal L-R output from the matrix circuit 1; 3 is a diode that compares the output signal of diode 2 with a preset reference value; if the former is greater than the latter, the output signal is "H"; This is a comparator that outputs a signal of "L" level if it is small. Here, the reference value is a voltage slightly higher than OV (ground potential). 4 is a timer, which always outputs a “L” level signal, and comparator 3
When the output of the comparator 3 falls from the "I-1" level to the "L" level, it is triggered and measures 4 minutes, and when the 4 minutes have elapsed, a signal of the "H° level" is output. When the output reaches the "■" level, it is reset and the output returns to the "L" level. SWI is a selection switch for switching between automatic and instantaneous.

On the other hand, 5 is the sum signal L' output from the matrix circuit 1
This is a delay circuit that delays +11, and is constituted by an eight-stage filter using an operational amplifier, and its output signal is supplied to the matrix circuit 6. The matrix circuit 6 adds the sum signal L+I''t and the above-mentioned signal RI and outputs it as a first addition signal La, and also adds the sum signal L+R and a signal obtained by inverting the signal RI, and subtracts the signal RI from the sum signal L+rL. ) and output as the second addition signal 11a.

Here, the sum signal L+R and the signal R have different frequency components, so if the signals La and R-a formed from the sum and difference of these signals are supplied to the left and right speakers, the sound will be as if it were a stereo broadcast. (pseudo stereo sound) can be generated.

Next, SW2 is the signal L output from the matrix circuit 6.
This is a selection switch for selecting one of the left and right audio signals applied to the input terminals TI and T2. This selection switch SW2 is a selection switch SV,'
1 is set to the automatic side, switching is performed by the signal output from timer 4, and selection switch S
When W1 is set to the manual side, switching is performed by a signal supplied via a manual operation switch (path shown). T3 is a terminal to which the left audio signal Ll is output, and T4 is a terminal to which the right audio signal R1 is output.

Next, the operation of the circuit shown in FIG. 1 mentioned above will be explained. First, the selection switch SWI is set to the automatic side as an initial condition of the circuit. Further, in the initial state, the output of the timer 4 is at the "L" level, and the selection switch SW2 is in the switching state shown by the solid line.

First, when different left audio signal R and right audio signal R are respectively applied to input terminals T I and T 2 (i.e.,
When a stereo audio signal is applied), the difference signal L-R output from the matrix circuit l becomes a voltage other than 0,
Therefore, the output of diode 2 becomes a positive voltage, and the output of comparator 3 becomes "H" level. In this case, timer 4 is not triggered and therefore selection switch SW
2 does not change, and the switching state of terminals T1.2 remains unchanged. T2 signal LJt
is output to the terminals L I and RI via the selection switch 4SW2.

Next, when the same left audio signal R and right audio signal R are applied to the input terminals T I and T 2 (when a monaural audio signal is applied), the difference signal L is output from the matrix circuit 1.
A 0 level signal is output as -4. This results in
A signal of 0 level is output from diode 2, and the output of comparator 3 falls to 0 level. At this falling edge, the timer 4 is triggered and starts measuring time for 4 minutes. If the signals at the input terminals T I and T 2 return to different signals before these four minutes have elapsed, the output of the diode 2 becomes a voltage other than 0, and the output of the comparator 3 becomes "H". The level returns and timer 4 is reset. In this case, there is no change in the output of the timer 4, and therefore in the switching state of the selection switch SW2 (the solid line state continues).

On the other hand, when the difference signal LR remains at 0 for 4 minutes, the output of the timer 4 rises to the "I" level.

As a result, the selection switch SW2 is switched to the broken line state, and the first addition signal La and the second addition signal Ra output from the matrix circuit 6 are output to the terminals T 3 and T, respectively.
Output to 4.

In this way, according to the above embodiment, the input terminals T1, T2
When a monaural audio signal is applied for 4 minutes or more, signals La and Ra are output from the output terminals T 3 and T 4 instead of the left and right audio signals R and R, respectively.

The details of the monaural-stereo conversion circuit MSK I according to the first embodiment of the present invention have been described above. This monaural-stereo conversion circuit MSKI may be inserted in the transmitting circuit or in the receiving circuit. FIG. 2 shows the insertion position when inserted into the transmitting circuit, and FIG. 3 shows the insertion position when inserted into the receiving circuit.

Next, a monaural stereo conversion circuit MSK2 according to a second embodiment of the present invention will be described.

Figure 4 shows a monaural-stereo conversion circuit M according to the same embodiment.
1 is a block diagram showing the configuration of SK2; in this diagram, parts corresponding to those in FIG. 1 are given the same reference numerals;
The explanation will be omitted.

In this figure, T5 is an input terminal to which the difference signal L-4 is applied, T6 is an input terminal to which the sum signal L+4 is applied, and SW
Reference numeral 3 denotes a selection switch for selecting either the difference signal L-R1 supplied from the input terminal T5 or the signal Da output from the delay circuit 5, and switching is performed by a signal output from the timer 4. T 7 and T 8 are output terminals.

Next, the operation of the circuit described above will be explained. First, in the initial state, the output of the timer 4 is at the "L" level, and the selection switch SW3 is in the solid line switching state. Here, the difference signal L between the left audio signal R and the right audio signal R, which are different from each other, is
-R and the sum signal L+R are applied to the input terminals T5 and T6, the output of the diode 2 becomes a positive voltage and the output of the comparator 3 becomes the "I4" level. in this case,
Timer 4 is not triggered and therefore selection switch S
The switching state of W3 remains unchanged, and the signal LR at terminal T5 is output to terminal T7 via selection switch SW3.
Signal L+R at terminal T6 is output to terminal T8.

Next, when the difference signal LR and sum signal L - + - R from the same left audio signal R and right audio signal R are continuously applied to the input terminal T5゜I6 for more than 4 minutes, the output of timer 4 Rikiji H
” level. This causes the selection switch SW to
3 is switched to the broken line state, and the output signal Da of the delay circuit 5
is output to terminal T7 via selection switch SW3.

The monaural-stereo conversion circuit MSK2 according to the second embodiment described above is inserted at the position shown in FIG. 2 when inserted into the transmitting circuit, and at the position shown in FIG. 3 when inserted into the receiving circuit. be done.

In addition, the above-mentioned 1. Comparing the second embodiment, the first
Although the circuit configuration of the second embodiment is simpler than that of the second embodiment, if either of these circuits is added as an additional device, the left audio signal L1 and the right audio signal R are relatively The first embodiment is easier to use because it is easier to take out from anywhere.

In addition, in PM stereo broadcasting, in order to ensure that the left audio signal R and right audio signal R can be demodulated without distortion,
A pilot signal is transmitted together with the difference signal L-R1 sum signal L+R. However, since this pilot signal is output during a stereo broadcast program even when a monaural record is used, it cannot be used as a signal for determining stereo/monaural. Therefore, in the embodiment described above, stereo/monaural is determined based on whether the difference signal L -Rh<O.

Further, in the above embodiment, the comparator 3 compares the output of the diode 2 with the reference value, but as shown in FIG. It may be possible to compare.

Further, in the above embodiment, if the time during which the monaural signal is applied is less than 4 minutes, the selection switch SW 2
, SW3 are not switched. This is to prevent malfunctions in the case of announcements and the like, even during stereo broadcasting, since the signals of the left and right channels may become the same for a short period of time.

"Effects of the Invention" As described above, according to the present invention, when reproducing monaural broadcasting, it is possible to output audio that can be recognized with a feeling similar to stereo broadcasting. Further, according to the present invention, since the pseudo stereo signal is switched based on the difference signal L-4, it is possible to switch based on the monaural stereo state of the actual sound source.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a monaural-to-stereo conversion circuit applying the pseudo-stereo system according to the first embodiment of the present invention, and FIG. 2 is a block diagram showing the configuration of the circuit shown in FIG. A block diagram showing the locations where the circuit shown in FIG.
The figure is a block diagram showing where the circuit shown in Fig. 1 and the circuit shown in Fig. 4 are interposed in the receiving circuit, and Fig. 4 shows monaural stereo conversion applying the pseudo-stereo system according to the second embodiment of the present invention. FIG. 5 is a block diagram showing the configuration of the circuit. FIG. 5 is a circuit diagram showing another +M configuration example of the comparator 3 in FIG. 1.6...Matrix circuit, 2...Diode, 3...Comparator, 5...
・Delay circuit, SW+. SW2. SW3...Selection switch.

Claims (2)

[Claims] (1) Adding the left audio signal and the right audio signal to form a sum signal, and forming a delayed sum signal by delaying this sum signal,
This delayed sum signal and the sum signal are added to form a first sum signal, and the sum signal and an inverted delayed sum signal, which is obtained by inverting the polarity of the delayed sum signal, are added to form a second sum signal. A pseudo-stereo system characterized in that one of the first and second added signals is output as a right channel audio signal, and the other is output as a left channel audio signal. (2) Take the sum and difference of the left audio signal and the right audio signal to form a sum signal and a difference signal, respectively, delay this sum signal to form a delayed sum signal, and combine this delayed sum signal and the sum signal. are added to form a first addition signal, and a second addition signal is formed by adding the sum signal and an inverted delayed sum signal obtained by inverting the polarity of the delayed sum signal, and the first and A pseudo-stereo system characterized in that either a second addition signal or a set of the left audio signal and the right audio signal is selected based on the level of the difference signal and output as left and right channel audio signals.