JPS6032267B2 - Control signal detection method in audio playback device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control signal detection method in an audio reproduction device.

Conventionally, audio playback devices commonly used for learning etc.
It is necessary to temporarily stop the device or return it to the starting position after each explanation or question, but listeners (students, etc.) had to operate the device manually each time.

In order to eliminate this manual operation by the listener, a control signal is pre-recorded on a recording medium, such as a magnetic tape or magnetic sheet, on a track separate from the audio signal track, and the device is automatically operated based on this control signal. Methods are also known, but the method of recording the control signal on a separate track from the audio signal has drawbacks such as making the device expensive and requiring extra space on the recording medium. There has been a strong demand for the development of a control system that allows audio signals and control signals to coexist without affecting the audio signals and without malfunctions. As a conventional example of this type,
A control signal consisting of a specific single frequency is provided in a band set on the high side or low side of the audio signal frequency band described in Publication No. 24529, and the control signal that has passed through a bandpass filter that allows this specific frequency to pass. A method for controlling the device is known, but in this method, if a specific signal on the lower side of the audio signal frequency band is selected, there are many noise components such as power supply hum, the S/N decreases, and noise is generated. and control signals cannot be distinguished, resulting in malfunctions.

When the level of a specific frequency is raised in order to increase this S/N ratio, the harmonic components of this specific frequency are able to compete, giving a feeling of discomfort in terms of purulent sensation. On the other hand, if a specific signal is selected above the audio frequency band, the level of the specific signal is likely to fluctuate due to variations between machines or devices during dubbing or transposition, resulting in control signal detection errors. Cheap. Furthermore, in order to eliminate such drawbacks, the audio signal frequency band must be narrowed, which has the drawback of degrading the sound quality of the audio signal. Further, as another conventional example, a specific frequency limit within the audio signal frequency band is described in Japanese Patent Publication No. 53-14206. (e.g. IKHZ) to another frequency na, (e.g. 10
0HZ) as a control signal, and the output of a bandpass filter that passes through . Attenuate and na. A method is also known in which a control signal is extracted based on the result of logical product with the output of a band removal filter that allows components other than those to pass. If there is a momentary presence of a signal that is modulated by a nearby frequency, malfunctions may occur.Also, the Q of the bandpass filter that passes through Na cannot be set high, and steep The disadvantage was that a strong damping castle could not be obtained. In order to eliminate the drawbacks of the conventional example, the present invention uses a control signal in which a sine wave carrier signal in the audible frequency range is amplitude-modulated with a modulation signal of a specific frequency, and detects and counts this control signal. have the means,
The present invention provides a reliable control signal detection method in an audio reproduction device by detecting the presence or absence of frequency components other than a carrier signal and distinguishing a control signal from an audio signal.

Hereinafter, embodiments will be described in detail with reference to the drawings. Figure 1 shows
This is a control signal waveform used in this embodiment.

That is, a sine wave with a frequency of HZ is used as a carrier signal,
Modulation degree 1 with a sine wave of frequency 20Hz as the modulation signal
Using an amplitude modulation signal of 00%, this can be expressed as a carrier signal.

= n sin ot modulation signal na, = sin t Amplitude modulation signal 〆AM=nsin↓ Toki e Sin(no.

The carrier frequency is 2000 Hz, the lower side wave frequency is 1, and the upper side wave frequency is 1 Nada OHZ.
2020th Z And the frequency spectrum of the amplitude modulated signal is the second
The result will be as shown in the figure.

The method of the present invention uses such an amplitude modulation signal as a control signal, records the general audio signal and this control signal alternately in one track of a recording medium, and distinguishes this control signal from the general audio signal during playback. The aim is to reliably distinguish and extract them.

FIG. 3 shows one embodiment of the control signal detection device of the present invention, and 1 includes a high-pass filter 8 for reducing low-frequency noise such as power supply hum, and a high-frequency noise of a preamplifier (not shown). a low-pass filter 9 for reducing the
2 is an audio burst wave detection section that has a rectifying and integrating circuit 12 and a comparator 13; 3 is a low-pass filter 14 that passes frequency components below the modulation frequency; 4 is a low-pass filter section having a Schmitt trigger circuit 15; 4 is a band removal filter 16 for removing only the carrier component; a non-carrier component frequency component detection section having a rectifying and integrating circuit 17; and a comparator 18; 5 is a counter section; 6 is an integrator, and 7 is a NAND circuit.

The output terminal of the signal amplification section 1 is connected to the input terminal of the audio burst wave detection section 2 and the input terminal of the frequency component outside the carrier component detection section 4, respectively, and the output terminal of the audio burst wave detection section 2 is connected to a low-pass filter. The output terminal of the low-pass filter section 3 is connected to one input terminal of the counter section 5 and the input terminal of the integrator 6, respectively. The output terminal is connected to the other input terminal of the counter section 5, the output terminal of the counter section 5 is connected to one input terminal of the NAND circuit 7, and the output terminal of the integrator 6 is connected to the other input terminal of the NAND circuit 7. connected to each terminal. Next, the operation of this embodiment will be explained.

First, an audio signal and a control signal are recorded on the recording medium, and during playback, both of these signals enter the preamplifier of the audio playback device through the playback head, and after being amplified, one is sent to the listener through the speaker. The other signal is input to the signal amplification section 1 of the control signal detection device shown in FIG. 3. The signal input to the signal amplifying section 1 is amplified, and at the same time, low-frequency and high-frequency noise components are suppressed by a low-pass filter 8 and a low-pass filter 9 and output. The signal waveform at the output terminal a of the signal amplifying section 1 is as shown in FIG. 4 a and a'.
The fact that the waveform a' of the control signal gradually decreases to a constant amplitude indicates the action of the AGCIO. now,
When the reproduced signal is a general audio signal, the audio signal input to the audio burst wave detection section 2 is rectified by a rectification/integration circuit 12 for signals exceeding a set level, integrated, and converted into a pulse wave by a comparator 13. (4th
Figure b).

This pulse wave is further applied to the low-pass filter section 3, and the envelope audio burst wave exceeding the modulation frequency of the control signal is removed by the low-pass filter section 14 (
(c) in Fig. 4, only the frequency components below this are waveform-shaped and output by the Schmitt trigger circuit 15 (Fig. 4c).
Figure d). This output signal is input to one input terminal of the counter section 5 and counted. On the other hand, the audio signal is also input to the non-carrier component frequency component detection section 4, where the frequency component corresponding to the carrier component of the control signal is removed by a band removal filter, and the other frequency components (Fig. 4 e) are rectified and integrated. The circuit 17 rectifies and integrates the signal, and the comparator 18 outputs it as a pulse wave (FIG. 4f). When this output signal is input to the other input terminal of the counter section 5, it is prevented from being output from the counter section 5. It has become. That is, if any signal is input from the non-carrier component frequency component detection section 4 to the other input terminal of the counter section 5, the counter section 5 is cleared and is not output. Next, when the reproduced signal is a control signal, this signal is an amplitude modulation signal obtained by 100% amplitude modulating the Fox HZ carrier signal with a 20Hz modulation signal, as described above, and this signal is used for audio burst wave detection. Pass through part 2 (
The control signal is output from the low-pass filter section 3 (FIG. 4 d') and input to the counter section 5 for counting, while the control signal input to the extra-carrier frequency component detection section 4 is Since the carrier component is removed by the band removal filter 16 that removes the carrier component, the output becomes zero (the fourth
Figures e' and f'), the counter section 5 detects that a set number of pulse signals from the low-pass filter section 3 have arrived within a set time, and during that time, the signal from the non-carrier component frequency component detection section 4 is detected. , there is no input to the other input terminal, so the counter section 5 outputs a pulse signal (
Figure 4g).

FIG. 5 shows the configuration of the counter section 5. When the output pulse of the low-pass filter section 3 (as shown in FIG. 4) is input to one terminal of the counter section 5, it is input to the AND circuit 19. When switching from the initial high level to the low level, the output of the AND circuit 19 becomes the /. level, which activates the monomulti circuit 20 and generates a pulse with a time width T, (for example, 22 secc) (Fig. 4). h'), the differentiating circuit 21 is activated at the rising timing of this pulse,
A trigger pulse is generated, and this trigger pulse operates the monomulti circuit 22, and the time width L (for example, 17 seconds) is generated.
A pulse is generated (Fig. 4').

By the output of this mono multi circuit 22, the NAND circuit 23
stops operating for T2 hours. On the other hand, mono multi circuit 20
The NAND circuit 24 is opened for a time T by the output of , and during this time the pulses from the low-pass filter section (as shown in FIG. 4) are input to the counter circuit 25 through the AND circuit 19 and the NAND circuit 24 and counted. Counter circuit 25
Then, a preset number of pulses are counted and, for example, at the falling edge of the 4th pulse, the output of the counter circuit switches from the high level to the low level, and this activates the differentiating circuit 26 to generate the trigger pulse. (Fig. 4 i'), and this trigger pulse is sent to the NAND circuit 2.
3. The NAND circuit 23 outputs an output only when the trigger pulse from the differentiating circuit 26 is input between the time widths T and T2 of each output pulse of the mono multi-circuits 20 and 22, and this output causes the mono multi-circuit 2
7 is activated, and the monomulti circuit 27 outputs a pulse with a time width T3 (for example, 1 ec) (Fig. 4g'). Furthermore, if any signal is output from the frequency component detection section other than the carrier component, it is input to the other input terminal of the counter section 5, and the output of the NOR circuit 28 is switched from high level to low level, thereby causing the counter circuit is cleared, so there is no output from the counter section 5. Note that the monomulti circuit 30 activated by the trigger pulse of the differentiating circuit 29 has a time width T4=3, for example.
A pulse of 0 hsec is output, and this is to maintain a no-signal period until the audio signal is interrupted and a control signal arrives. In this embodiment, an integrator 6 and a NAND circuit 7 are further provided, but these are used to prevent the playback device from performing operations such as a pause while the control signal continues. Pulse signal (Fig. 4g)
) is input to one input terminal of the NAND circuit 7, and
Even if the signal input from the low-pass filter section 3 to the integrator 6 is rectified and integrated (k' in Figure 4) and input to the other terminal of the NAND circuit 7, while the signal from the integrator 6 continues. The AND condition is not established between this signal and the pulse signal from the counter section 5, so the NAND circuit 7 is closed, and when the signal from the integrator 6 is interrupted, the AND condition of the NAND circuit 7 is satisfied. Established, the NAND circuit 7 outputs a pulse signal (FIG. 4, 1').

In this way, audio signals and control signals can be reliably discriminated and
The pulse signal outputted from the NAND circuit 7 by reproducing the control signal can be used as a signal for automatically controlling the pause and repeated reproduction operations of the audio reproduction device. In addition, can. The signal reproduced by the speakers, which is the amplitude modulated signal of the Fox Day 2 carrier signal used as the control signal, has a tone similar to the chirping of a corrugated cricket, giving the listener a pleasant feeling and a sense of wisteria. As explained above, according to the present invention, a control signal obtained by amplitude modulating a sinusoidal carrier signal in the audible frequency range with a modulation signal of a certain specific frequency is used, and when the arrival of this control signal is detected and counted. By discriminating the control signal from the audio signal by outputting it from the counter section on the condition that no frequency components other than the carrier component arrive at the same time, the sound quality of the audio signal is not degraded, and the influence of noise and level fluctuations is eliminated. This has the advantage that the control signal can be reliably detected without being affected.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the waveform of an amplitude modulated signal, FIG. 2 is a diagram showing a frequency spectrum of an amplitude modulated signal, and FIG. 3 is an electrical diagram of a control signal detection device according to the method of the present invention. Circuit block diagram, Figure 4 is similar to Figures 3 and 5.
FIG. 5 is a diagram showing input and output waveforms of the device shown in FIG. 5, and is a block diagram of the electric circuit of the counter section. 1... Signal amplification section, 3... Audio burst wave detection section, 3... Low pass filter section, 4... Frequency component detection section other than carrier component, 6... Counter Part, 10...AGC circuit, 1 1...
Amplifier, 1 2, 17... Rectifier/integrator circuit, 13
, 18... Comparator, 14... Low pass filter, 15... Schmitt trigger circuit, 16...
...Band removal filter. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] 1. An amplifier including an AGC circuit for amplifying an audio signal recorded and reproduced in one track of a recording medium and a control signal obtained by amplitude modulating a carrier signal in an audible frequency range with a modulation signal of a certain frequency. a signal amplifying section having a rectifying/integrating circuit and a comparator, and an audio burst wave detecting section for outputting a pulse corresponding to a signal having a predetermined amplitude or more of the amplified signal; a low-pass filter; A low-pass filter section that has a Schmitt trigger circuit, passes frequency components lower than the modulation signal of the output pulse of the audio burst wave detection section, and outputs a waveform-shaped pulse, a band removal filter, a rectification and integration circuit, and a comparison. a carrier component frequency for removing only the carrier signal component of the output of the signal amplifying section, passing other frequency components, and outputting a pulse corresponding to a signal having a predetermined amplitude or more; A component detection section counts the number of pulses input from the low-pass filter section to one terminal within a set time, and does not output when a pulse from the frequency component detection section other than the carrier component is input to the other terminal. and a counter section configured such that when an audio signal is reproduced, the pulse from the frequency component detection section other than the carrier component is inputted to the other terminal of the counter section so that the pulse is not outputted from the counter section, and control is performed. In the audio reproducing device, wherein when a signal is reproduced, the counter section counts the number of pulses input from the low-pass filter section to one terminal, thereby obtaining an output from the counter section. Control signal detection method.