JPH0279300A - Sound recording/reproducing device - Google Patents

Abstract

PURPOSE:To simplify a circuit constitution, and to match the characteristics at the time of a sound recording operation and at the time of a reproducing operation by using a low pass filter, which is provided so as to interrupt high band signals unnecessary at the time of the sound recording operation, at the time of the reproducing operation as well. CONSTITUTION:An ADPCM analyzing/synthesizing circuit 8 to analyze and synthesize a voice in an ADPCM system at the time of the sound recording and reproducing operations, a control circuit 20 to control the write operation of a digital signal outputted from the ADPCM analyzing/synthesizing circuit 8 to a semiconductor memory circuit 18 and the read operation of the signal stored into the semiconductor memory circuit 18, and low pass filters 4 and 5 to interrupt the high band signal unnecessary at the time of the sound recording and reproducing operations constitute the title device. Further, the low pass filters 4 and 5 provided so as to interrupt the high band signal unnecessary at the time of the sound recording operation are used at the time of the reproducing operation as well. Thus, the circuit constitution can be simplified.

Description

Detailed Description of the Invention (a) Industrial Application Field The present invention converts a recording signal obtained from a microphone into a digital signal and stores it in a semiconductor memory circuit, and also stores it in the semiconductor memory circuit during playback operation. The present invention relates to an audio recording and reproducing device that reads out a signal, converts it into an analog signal, and outputs the sound through a speaker.

(B) Conventional Technology Cassette tape recorders, which use magnetic tape called cassette tape, have become popular as devices for recording and playing back audio. Devices such as cassette tape recorders that use magnetic tape as a means of recording audio signals have the advantage of being able to perform long recording operations, but they are difficult to miniaturize. Since it requires a mechanism to drive the magnetic tape, there is a problem in that the failure rate is high. A device that improves on these points converts audio signals into digital signals and stores them in a semiconductor memory circuit, and during playback, reads out the signals stored in the semiconductor memory circuit, converts them into analog signals, and emits them through a speaker. Techniques have been developed to make sounds, such as the one disclosed in Japanese Patent Application Laid-Open No. 62-266786, for example.

(c) Problems to be Solved by the Invention A device configured to store an audio signal in a semiconductor memory circuit and to read out and reproduce the signal stored in the semiconductor memory circuit is disclosed in the above-mentioned publication. As shown, it is equipped with a low-pass filter that blocks out high-frequency signals. In the conventional technology, such low-pass filters were provided separately for recording and playback, resulting in a complicated circuit configuration. The present invention aims to provide a device that improves this point.

(2) Means for Solving the Problems The present invention provides an ADPCM analysis and synthesis circuit that performs voice analysis and voice synthesis using the ADPCM method during recording and playback operations;
A control circuit that controls the writing operation of the digital signal whose output is distorted from the ADPCM analysis and synthesis circuit to the semiconductor memory circuit and the reading operation of the signal stored in the semiconductor memory circuit, and the control circuit that controls the operation of writing the digital signal whose output is distorted from the ADPCM analysis and synthesis circuit and the reading operation of the signal stored in the semiconductor memory circuit; It consists of a low-pass filter that cuts out high-frequency signals.

(*) Function In the present invention, the low-pass filter provided to cut off unnecessary high-frequency signals during recording operation is also used during playback operation.

(v) Embodiment The illustrated circuit is an embodiment of the present invention, in which (1) is a microphone that converts an acoustic signal into an electrical signal, and (2) is a microphone that converts an acoustic signal into an electrical signal. There is a recording amplifier circuit T to which a recording signal converted into a non-signal is input and which amplifies the signal. (3) is H (high) at the control terminal (3c)
An electronic switch (4) that is opened when a level signal is applied is used to input the recording signal amplified by the recording amplifier circuit (2) through the electronic switch (3) and eliminate unnecessary high frequencies. 10th block of signal
The bus filter <5) is a 20th pass filter to which the signal passed through the 10th bus filter (4) is applied, and its cutoff frequency is lower than the cutoff frequency of the 10th bus filter (4). The settings are complete. (6
) is an electronic switch that is closed when an H level signal is applied to the control terminal (6C), and (7) is an electronic switch that closes the 10th bus filter (4) and the 20th bus filter (5). An A-D converter converts the analog signal passed through the electronic switch (6) into a digital signal, and (8) is an ADP that performs digital processing using a method called ADPCM, that is, adaptive differential pulse code modulation.
CM analysis synthesis circuit, (9) is the ADPCM that reproduces action poems.
This is a DA converter that converts the digital signal processed by the analysis/synthesis circuit (8) into an analog signal. (10
) is an electronic switch connected to guide the playback signal converted by the D-A converter (9) to the tenth bus filter (4), and the control terminal (
10c) is configured to be closed when an H level signal is applied to the terminal 10c). (11) is the control terminal (li
(12) is an electronic switch that is closed when the H level signal is fully applied to (e);
) is an electronic volume that adjusts the level of the playback signal input through the control terminal (12c) that adjusts the level.
). (13) is the electronic volume (12
) is input with a level-adjusted playback signal and amplifies the signal; (14) is a playback amplifier circuit (14) which emits the signal as soon as the playback signal amplified by the playback amplifier circuit (13) is applied. It is a speaker that does. (1
5) is a control unit that controls the analysis operation and synthesis operation of the ADPCM analysis and synthesis circuit (8), and (16) is an external circuit, the control unit (15), and the ADPCM analysis and synthesis circuit (8).
This is a data I10 buffer circuit that controls the input/output operation of signals between the data I10 and the data I10 buffer circuit. In such a circuit, an A-D converter (
7), ADPCM analysis and synthesis circuit (8), D-A converter (
9), control unit (15) and buffer circuit (1)
6) constitutes the audio processing port m<■>, and such a circuit is, for example, manufactured by Oki Electric Industry Co., Ltd. (7) LS I'
MSM6258'' etc. 1 may be used, and the details thereof will be omitted. (18) is data that constitutes the audio processing circuit (17)! 10 RAM, which is a semiconductor memory that stores digital signals output from the buffer circuit (16);
<19> is an address control circuit that controls the write operation and read operation of signals to the RAM (1B), and (20) is an address control circuit that controls the audio processing circuit (■), the RAM (18), the address control circuit (19), etc. This is a control circuit that controls operations.

(21) is a recording operation switch that is pressed and closed when the audio signal is stored in the RAM (18), and (22) is pressed when the signal stored in the RAM (18) is read out and played back. Regeneration operation switch to be closed (23)
is a stop operation switch that is pressed and closed during stop operation, (2
4) is a volume adjustment operation switch that is operated when adjusting the volume;
Reference numeral 25 denotes a storage time changeover switch that changes the storage time in the RAM (18) by changing the sampling frequency, and is configured to be closed when performing a long-time storage operation.

(26) is a switching signal output terminal provided in the control circuit (20), and is a switching signal output terminal provided in the control circuit (20).
) is open, it outputs an H level signal, and when the changeover switch (25) is closed, it outputs an L (low) level signal. (
27) is connected to bypass the 20th bus filter (5), and H is connected to the control terminal (27c).
an electronic switch that is in a closed state when a level signal is applied and bypasses the 20th bus filter (5), and its control terminal (27c) is connected to the switching signal output terminal (26). ing. (28) is a volume adjustment signal output terminal that outputs a control signal for volume adjustment in response to the operation of the volume adjustment operation switch (24);
It is connected to the control terminal (12c) of the electronic volume (12).

(29) is a recording switching signal output terminal which outputs an H level signal when the recording operation switch (21) is pressed and closed, and is a control terminal (3c) of the electronic switches (3) and (6). ) (6c). (3o) is a regeneration switching signal output terminal that outputs an H level signal when the regeneration operation switch (22) is pressed and closed;
The control terminal (10e) of the electronic switch (IQ) (11)
) (llc).

The present invention is constructed as described above, and its operation will be explained next. When performing a normal storage operation, that is, when the storage time selection switch (25) is in the open state, the sampling frequency in the audio processing circuit (■) is set to 8 KHz,
If the number of quantization bits is 4, the bit rate will be 32 bits/second, and if the capacity of the RAM (18) is 2 Mbits, data can be stored for about 64 seconds. Further, if the sampling frequency is 4 KHz and the number of quantization bits is 4 when the storage time changeover switch (25) is in the open state, the bit rate is 16 bits/second, and the RA
It is possible to store information in M (18) for approximately 128 seconds. When the sampling frequency is set to such a frequency, the cutoff frequency of the 10th pass filter (4) is set to 4 KHz, and the cutoff frequency of the 20th pass filter (5) is set to 2 KHz. I can't do it.

Further, the analysis and synthesis processing by the ADPCM analysis and synthesis circuit (8) and the write operation to the RAM (18>) accompanying the processing are performed in 1-second intervals.In other words, the audio processing circuit (
The analysis and synthesis operation by the ADPCM analysis and synthesis circuit (8) is started by the start signal output from the control section (15) incorporated in the control section (15) built in the control section (15) after one second.
) The analysis and synthesis operation is stopped by the stop signal output from the terminal. When a signal is written to the RAM (18), that is, during a recording operation, the signal analyzed and processed by the ADPCM analysis and synthesis circuit (8) for one second is transferred to the data I1.
The data is outputted to the RAM (18) through the 0 buffer circuit (16) and written into the RAM (18) with an address specified by the control operation of the address control circuit (19). In addition, when reading a signal from the RAM (1B), that is, during a reproduction operation, the ADPC is
The signal that has been synthesized by the M analysis and synthesis circuit (8) is D-
The signal is input to the A converter (9) and converted into an analog signal. The control operation of the RAM (1B) is performed by the audio processing circuit (■) and the address control circuit (19) in this way.Next, each operation in this embodiment will be explained.

First, a description will be given of the case when the storage time changeover switch (25) is in the open state, that is, the normal recording operation.

When a recording operation is performed in such a state, power is supplied to each circuit, the recording operation switch (21) is suppressed and opened, and the control circuit (20) performs a control operation for recording. In this state, an H level signal is output to the switching signal output terminal (26) provided in the control circuit (20), so the electronic switch (27) is in the open state and the 20th-bus It is in a state of bypassing the filter (5). Also, recording switching signal output terminal (2
Since the H level signal is output to 9), the electronic switch (
3) and (6) are in the open state, but since an L level signal is output to the reproduction switching signal output terminal (30), the electronic switches (10) and (11) are in the open state. The recording signal converted into an electric signal by the microphone (1) is input to a recording amplifier circuit (2) where it is amplified and then passed through an electronic switch (3) to a tenth pass filter (4).
) is entered. The recording signal input to the 10th pass filter (4) is filtered by an electronic switch (27) after removing unnecessary high-frequency signals, that is, signals with frequencies higher than 4KH2.
and is input to the audio processing circuit (■) through (6).

The recording signal input to the audio processing circuit (■) is A-
The D converter (7) converts the signal into a digital signal, and the ADPCM analysis/synthesis circuit (8) analyzes the signal for one second at a time, as described above. In addition, the ADP
The signal that has been analyzed and processed by the CM analysis and synthesis circuit (8) is
RAM (1) through data I10 buffer circuit (16)
B> and written to RAM (18) by the control operation of the address control circuit (19). While the recording operation is being performed, the analysis operation by the ADPCM analysis and synthesis circuit (8>) and the writing operation to the RAM (1B) are stopped until the operation is stopped or the RAM (18)
This will be repeated until the capacity is exhausted. Although the normal recording operation is performed in this way, next we will explain the long recording operation when the storage time changeover switch (25) is in the open state, that is, the long recording operation. When the storage time changeover switch (25) is in the open state, the control circuit (20)
Since an L level signal is output to the switching signal output terminal (26) provided in the electronic switch (27), the electronic switch (27) is in an open state. In such a state, the recording signal amplified by the recording amplifier circuit (2) is transferred to the electronic switch (
3) is input to the 10th pass filter (4), and after removing signals with frequencies higher than 4 KHz, the 20th
- Can be input to pass filter (5). The recording signal that has been input to the 20th bass filter (5) is filtered of unnecessary high-frequency signals during long-term recording operation, that is, signals with frequencies higher than 2 KHz, and then passed through the electronic switch (6) to the audio processing circuit ( ■) is input. The audio processing circuit (■
) is input to the RA by the operation described above.
M (1B), but since the sampling frequency has been switched from 8 KHz to 4 KHz, the R
The time recorded in A M (18) is twice as long as in normal recording operation.

Although the recording operation is performed as described above, the reproduction operation will be explained next. When the playback operation is performed, the playback amplifier circuit (13
), etc., and the playback operation switch (2
2> is pressed closed, and the control circuit (20) performs a control operation for regeneration. When such a switching operation is performed, an H level signal is output to the playback switching signal output terminal (30), so the electronic switches (10) and (11) are in the closed state, but the recording switching signal output terminal ( 29) is L
Since the level signal is output, the electronic switch (3) (6
) is in the open state. The signals stored in the RAM (18) are read out by the control operation by the address control circuit (19) and are also read out by the data I10 buffer circuit (16).
) can be input to the ADPCM analysis and synthesis circuit (8). The digital signals input to the ADPCM analysis and synthesis circuit (8) are synthesized by the ADPCM analysis and synthesis circuit (8) for one second each, and then applied to the DA converter (9) where they are converted into analog signals. Ru. In this way, the processing operation by the audio processing circuit (■) is performed, but at this time, the switching operation between normal time operation and long time operation is performed using RAM (1
8) and the output level of the switching signal output terminal (26) provided in the control circuit (20) is automatically switched based on the information. The reproduced signal converted into an analog signal by the DA converter (9) is input to a tenth bass filter (4) through an electronic switch (10), and unnecessary high-frequency signals are removed. The reproduced signal that has passed through the 10th bus filter (4) is passed through the electronic switch (27) (11) or the 20th pass filter (5) and the electronic switch (11).
is inputted to the electronic volume (12) through. The level of the playback signal input to the electronic volume (12) is adjusted based on the control signal output from the volume adjustment signal output terminal (28) in accordance with the operation of the volume adjustment operation switch (24). be done. The reproduction signal whose level has been adjusted by the electronic volumetric volume (12) is sent to the reproduction amplifier circuit (13).
), the signal is amplified, and then applied to the speaker (14) to emit sound. While the playback operation is being performed, the readout operation from the RAM (18) and the ADPCM
The synthesis operation by the analysis and synthesis circuit (8) will be performed until a stop operation is performed or until there are no more signals written in the RAM (18).

Note that by increasing the capacity of RAM (18), the recording and playback time can be increased. In addition, if the RAM (18) is built into a container called an IC card and the IC card (RAM <18>) is made replaceable, it can be used as a recording means in place of a tape recorder even if the RAM (18) has a small capacity. I can do it.

(G) Effects of the Invention The audio recording and playback device of the present invention uses the low-pass filter provided to cut off unnecessary high-frequency signals during the recording operation also during the playback operation. Compared to the conventional technology using two low-pass filters, this has the advantage that the circuit configuration is simpler and the characteristics during recording and playback operations can be matched.

[Brief explanation of the drawing]

The illustrated circuit is one embodiment of the invention. Explanation of main drawing numbers (1)... Microphone, (2)... Recording amplification port Q, (4)... 10th bass filter, (5)...
...20th-pass filter, (8)...ADPC
M analysis synthesis circuit, (12)...electronic volume, (
13>... Reproduction amplifier circuit, (14)... Speaker, (15)... Control unit, (16)... Data I10 buffer circuit, (ν)... Audio processing circuit,
(1B> RAM, (19)...address control circuit, (20)...control circuit.

Claims (1)

[Claims] (1) Convert the recording signal obtained from the microphone into a digital signal and store it in a semiconductor memory circuit, and during playback operation, read out the signal stored in the semiconductor memory circuit, convert it into an analog signal, and emit it through a speaker. In a voice recording and playback device configured to produce sound, an ADPCM analysis and synthesis circuit that performs voice analysis and voice synthesis using an ADPCM method during recording and playback operations;
a control circuit that controls writing of digital signals output from the analysis and synthesis circuit to the semiconductor memory circuit and readout of signals stored in the semiconductor memory circuit, and a microphone and the ADPCM analysis and synthesis circuit; It consists of a low-pass filter that is inserted and connected and cuts off unnecessary high-frequency signals.
A voice recording/playback device characterized in that a playback signal output from a DPCM analysis/synthesis circuit is guided to a playback amplifier circuit through the low-pass filter.