JPH01302399A - Sound signal recoding circuit - Google Patents

Abstract

PURPOSE:To improve the accuracy and stability of a circuit characteristic as to a sound signal by executing a digital pre-emphasis processing to a digital sound signal before written to a memory. CONSTITUTION:The sound signal digital-converted by an A/D converter 10 is sent to a pre-emphasis circuit 12, and the pre-emphasis processing is digitally executed to the sound signal to be digital-converted there. Since the pre-emphasis processing reduces the influence of a high band noise as to the sound signal in a condition in which the sound signal is recorded to a recording disk Dc. it is the processing to raise a gain as the band of the components is high according to the frequency band of the sound signal. The pre-emphasis circuit 12 is composed of, for example, plural multipliers, adders, and delaying circuits. In such a way, by executing the pre-emphasis processing to the sound signal before time-base-compressed, the pre-emphasis processing can be executed in which the high accuracy and excellent stability are secured.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to an audio signal recording circuit for time-base compressing an audio signal, frequency modulating the signal, and recording the resulting signal on, for example, a recording disk.

B0 Summary of the Invention The present invention provides an audio signal recording circuit that compresses the time axis of a digital audio signal using a memory, converts it into analog, modulates the frequency, and records the signal on a recording disk, etc. By performing digital pre-emphasis processing on the audio signal, it is possible to improve the accuracy and stability of the circuit characteristics of the audio signal, and to improve the accuracy and stability of the audio signal after time-base compression using the memory described above. An audio signal recording circuit is provided, which is capable of accurately recording and reproducing control information signals by preventing multi-emphasis processing of control information signals added to the input signal, and accurately recording and reproducing audio signals. This is what we provide.

C1 Prior Art Conventionally, for example, in so-called still video camera devices, audio signal recording circuits have been used to record not only image signals but also audio signals on recording disks such as magnetic disks.

For example, the applicant has previously proposed JP-A-61-
In the audio signal recording circuit described in Japanese Patent No. 109389, as shown in FIG. 6, an audio signal, which is an analog signal, is input to a compressor 101 that performs amplitude compression based on a predetermined compression ratio. This compressor 101
The audio signal that has passed through A is passed through a low-pass filter 102.
/D (analog/digital) converter 103 performs digital conversion. The above low-pass filter 102
is intended to reduce so-called aliasing noise that occurs during digital conversion in the A/D converter 103.

The audio signal digitally converted by the A/D converter 103 is written into a memory 105 controlled by a memory controller 104 serving as a time-base compression circuit.

The audio signal written in the memory 105 is read out at a faster speed than it is written, thereby compressing the time axis. The ratio between the writing speed of the audio signal to the memory 105 and the reading speed of the audio signal from the memory 105 is the compression ratio of the time axis compression.

Then, the audio signal As read from the memory 105 is
is sent to adder 106. In this adder 106, various control information signals, such as start and end identification signals SID and ErD, and information signal API are added to the audio signal As.

The start and end identification signals SrD and EID are generated by a predetermined identification signal generation circuit, and the audio signal A
This is a signal that indicates the start position and end position of the recording of the audio signal AS in a state where the audio signal AS is recorded on the recording disk. The information signal API is generated by a predetermined information signal generation circuit, and when reproducing the audio signal As recorded on the recording disk, the information signal API contains predetermined information for controlling a reproduction device that reproduces the audio signal As. This is the signal to be displayed.

The above audio signal As, the above start and end identification signal S
As shown in FIG. 7, the ID, EID, and the information signal API are arranged in a predetermined order, for example, the start identification signal AID, the information signal API, the audio signal AS, and the end identification signal EID. D/A (digital/analog) converter 1
Sent to 07.

The D/A converter 107 converts the sent signal into analog and sends it to a pre-emphasis circuit 109 via a low-pass filter 108 for noise reduction.

The pre-emphasis circuit 109 performs pre-emphasis processing on the signal to be sent. This pre-emphasis processing is performed to prevent the occurrence of so-called triangular noise when the signal is frequency modulated. This is a process to increase the The transfer characteristic E (S) in this pre-emphasis circuit 109 is expressed as follows. In the equation showing this transfer characteristic E (s), each time constant Ts + 72 + Ts is determined according to the former 7) of signal recording on the recording disk. If the image signal of the system is to be recorded, T+=0.06903, T2=0. 277
ns, T3=0.19 Ins.

The signal that has passed through the pre-emphasis circuit 109 is passed through a limiter 11 that cuts off signals exceeding a predetermined amplitude.
0 to the FM modulation circuit 111 that performs frequency modulation. This FM modulation circuit 111 modulates the sent signal into an FM signal having a predetermined carrier frequency, and sends it to a predetermined recording device such as a recording head. This recording device is
The M signal is recorded on a recording disk such as a magnetic disk.

To play the audio signal recorded as described above,
After reproducing the signal recorded on the recording disk using a reproducing head or the like and performing FM demodulation, de-emphasis processing, which is the reverse of the pre-emphasis processing, is performed.

The transfer characteristic in this de-emphasis processing is the reciprocal of the transfer characteristic in the pre-emphasis processing. Therefore, the above-mentioned pre-emphasis processing and the above-mentioned de-emphasis processing work complementarily during recording and playback, and the frequency characteristic of the amplitude ratio becomes flat for the time-axis compressed audio signal, and the FM modulation and FM Only the so-called triangular noise associated with demodulation is removed.

Then, by sequentially performing the operations reverse to those of the recording system as described above, the time axis is extended and an analog audio signal is obtained.

Problems to be solved by the D0 invention By the way, in the audio signal recording circuit as described above,
Since the pre-emphasis circuit and the de-emphasis circuit are analog circuits each composed of an active element, a resistor element, a capacitor, etc., there is a problem that the absolute accuracy and temperature/humidity characteristics of each element are unstable.

In addition, during the pre-emphasis processing, the start and end identification signals SID, E[D and the information signal API
The same pre-emphasis processing as the above-mentioned audio signal As is also applied to the audio signal As.

Since each of the above-mentioned identification signals and the above-mentioned information signals contain many high-frequency components, the above-mentioned pre-emphasis processing causes the start and end portions of each of the above-mentioned identification signals to be Overshoot and undershoot may occur, and the level of the high-frequency information signal API may be made high overall.

That is, the transmission speed of the information signal API is, for example, N
If the TSC-based recording format is used, 1. 7
9 Mb i t/sec, and in this case, signal components ranging from the lowest component close to direct current to the highest repetition frequency exceeding 895 kHz are included, and are not affected by the high frequency enhancement effect of the pre-emphasis processing described above. easy.

As a result of the pre-emphasis processing, the portion exceeding a predetermined signal level is recorded on the recording disk with the amplitude limited by the limiter 110. Therefore, the signal recorded on this recording disk is reproduced and de-emphasized. In the processed signal, each identification signal and information signal added in the adder 106 will not be accurately reproduced. Therefore, there is a possibility that the audio signal cannot be reproduced accurately.

SUMMARY OF THE INVENTION The present invention is proposed in view of the above-mentioned circumstances, and improves the accuracy and stability of pre-emphasis processing, and also improves the accuracy and stability of pre-emphasis processing. It is an object of the present invention to provide an audio signal recording circuit that can accurately record the identification signal, information signal, etc., and accurately reproduce the identification signal, information signal, etc., thereby accurately reproducing the audio signal.

80 Means for Solving the Problems In order to solve the above problems and achieve the above objects, an audio signal recording circuit according to the present invention includes an analog/digital converter that digitally converts an input analog audio signal;
a pre-emphasis circuit that performs pre-emphasis processing on the digital audio signal output from the analog/digital converter; a time-base compression circuit that performs time-base compression processing on the digital audio signal that has been subjected to the pre-emphasis processing; An adder that adds a control information signal to the digital audio signal output from the compression circuit, a digital/analog converter that converts the output signal of the adder into analog, and an analog audio signal output from the digital/analog converter. and a modulator that frequency modulates the frequency.

F0 operation In the audio signal recording circuit according to the present invention, pre-emphasis processing is performed on the audio signal after digital conversion but before time-base compression, so the accuracy and stability of the pre-emphasis processing is ensured. At the same time, the control information signal added to the time-axis compressed audio signal is not subjected to pre-emphasis processing.

G. Examples Specific examples of the present invention will be described below with reference to the drawings.

This embodiment is an example in which the audio signal recording circuit according to the present invention is applied to a so-called still video camera device configured to record still images on a magnetic disk serving as a recording disk.

In the image signal recording circuit of this still video camera device, as shown in FIG. 1, an image signal obtained by an imaging device such as a COD is supplied to a video signal input terminal 1. The video signal supplied to the video signal input terminal 1 is converted into a predetermined video recording signal by the conversion circuit 2. The signal is then sent via a video signal pre-emphasis circuit 3 with non-linear characteristics and a video/audio changeover switch 4 to an FM modulation circuit 5 that performs frequency modulation. This FM modulation circuit 5 converts the supplied signal into an FFM having a predetermined carrier frequency.
The signal is modulated into an M signal and sent to the recording head 6. The recording head 6 is brought into sliding contact with the magnetic disk Dc, and records the sent FM signal onto the magnetic disk DC. The magnetic disk Dc is rotationally driven by a predetermined rotation drive means at a predetermined rotation speed (for example, 3600 rpm).

In the audio signal recording circuit according to the present invention, as shown in FIG. 1, an audio signal obtained from, for example, an acoustic transducer such as a microphone is input to the audio signal input terminal 7. This audio signal is sent to a compressor 8 where it is amplitude compressed, and passed through a low pass filter 9 to an A/D
The signal is sent to a converter (analog/digital converter) 10.

The above-mentioned low-pass filter 9 is connected to the above-mentioned A/D converter 7
This is to reduce so-called aliasing noise that occurs when an audio signal is converted into a digital signal. The A/D converter 10 is supplied with a sampling signal of a predetermined frequency (for example, 11.2 KHz) from a first oscillator 11. This A/D converter 10
The signal conversion in is performed based on the sampling signal, and is converted into a digital signal in which one word consists of 8 bits, for example.

The audio signal digitally converted by the A/D converter 10 is sent to a pre-emphasis circuit 12. This pre-emphasis circuit 12 is a circuit that digitally performs pre-emphasis processing on a digitally converted audio signal.

This pre-emphasis processing is performed to reduce the influence of high-frequency noise on the audio signal when the audio signal is recorded on the recording disk Dc. This is a process of increasing the gain. The pre-emphasis circuit 12 is
For example, as shown in FIG. 2, it is composed of a plurality of multipliers, adders, and delay circuits. That is, in the pre-emphasis circuit 12 shown in FIG. 2, the input digital signal is input to the first adder I. This first adder p! The output signal of is sent to the first delay circuit d1 and the first multiplier.

The output signal of the first delay circuit d1 is sent to a second multiplier 2 and a third multiplier 3. The output signal of the second multiplier 2 is sent to the first adder pI and added to the digital signal input to the pre-emphasis circuit 12. The output signal of the first multiplier kl and the output signal of 3 to the third multiplier are the same as the output signal of the second adder p2.
are added to each other. The output signal of this second adder p2 is sent to a third adder p3. The output signal of this third adder p3 is sent to a second delay circuit d2 and a fourth multiplier 4. The output signal of the second delay circuit d2 is sent to a fifth multiplier 5 and a sixth multiplier 8. The output signal of the fifth multiplier 5 is sent to the third adder p3 and added to the output signal of the second adder p2.

The output signal of 4 to the fourth multiplier and the output signal of 6 to the sixth multiplier are added together by a fourth adder p4. The output signal of this fourth adder p4 becomes the output signal of this pre-emphasis circuit 12.

Note that the first to sixth multipliers kl+...k8
For example, the coefficient to be multiplied in is 3.4031 at 1 in the first multiplier, 0.5944 at 2 in the second multiplier, and -2 at 3 in the third multiplier.
,9975, and 2,408 in 4 to the fourth multiplier above.
8, the fifth multiplier is set to 0.5936, and the sixth multiplier is set to -2,0024. Further, the first and second delay circuits d
,, the delay time in a2 is determined according to the compression rate during time axis compression of the audio signal, which will be described later. For example, when the compression rate is 320 times, it is 11.175 ps, and the compression rate is 64
In the case of 0 times, 22.349! I3, compression ratio is 128
In the case of 0 times, it is determined as 44.698p3. By determining the coefficients used in each of the multipliers and the delay times in each of the delay circuits as described above, the characteristics of this pre-emphasis circuit can be set to a predetermined amplitude ratio for each frequency band, as shown in FIG. This allows the output signal to be obtained.

As described above, in the audio signal recording circuit according to the present invention, since the pre-emphasis processing is performed by the digital circuit, the pre-emphasis processing is performed with high precision, and also the change in processing characteristics due to fluctuations in temperature and humidity can be avoided. Furthermore, since there are few differences in characteristics between circuits constructed in the same way, compatibility between devices is ensured.

The audio signal that has passed through the pre-emphasis circuit 12 is filtered through a low-pass filter 13 for reducing so-called aliasing noise.
The signal is then sent to the memory device 14, which serves as a time axis compression circuit. This memory device 14 has a memory controller 15 controlling the speed at which signals are successively written. This memory controller 15 controls writing of the audio signal to the memory device 14 based on the sampling signal supplied from the first transmitter 11, and also controls writing of the audio signal to the second transmitter 11.
Based on the readout control signal supplied from the transmitter 16 of
Controls reading of audio signals from the memory device 14. The readout control signal supplied by the second oscillator 16 is
A predetermined frequency (for example, 640 times) with a predetermined magnification is applied to the sampling signal supplied by the first oscillator 11.
For example, the frequency is 7°16 MHz).Therefore, the reading of the signal from the memory device 14 is limited to the memory device 1.
4, the signal is compressed on the time axis using the compression ratio of the read control signal with respect to the sampling signal.

The writing/reading timing of signals for the memory device 14 is controlled by the memory controller 15 (7!). I will be treated. The memory controller 15 is supplied with a write start signal and a read start signal from a timing generation circuit 17.

The write start signal is a signal for starting writing of an audio signal in the memory device 14,
It is generated by the timing generation circuit 17 when an operation signal is supplied to the operation signal input terminal 18 connected to the timing generation circuit. The operation signal is generated by operating a shirt button (not shown).

The read start signal is a signal that instructs the timing to start reading the audio signal in the memory device 14. This successive star No. 1 is the magnetic disk D
When it is detected that the recording head 6 is at a predetermined position to record the audio signal on the magnetic disk DC, based on the output signal of the detection head 19 that is in sliding contact with the magnetic disk DC,
It is generated by the timing generation circuit 17 mentioned above. As shown in FIG. 4, the positions at which the audio signals on the magnetic disk Dc are to be recorded are defined as four recording tracks Tll formed concentrically on the magnetic disk DC at equal angular intervals. The positions correspond to the first to fourth segments Sat+ So2+ Sa3+Saa, for example, 1 for the entire circumference of the magnetic disk D0.
It is detected based on the PC signal recorded at the location.

The audio signal AS read from the memory device I4 is sent to the adder 20. This adder 20 receives the audio signal AS and various control information signals, such as a start and end identification signal Sr generated by an identification signal generation circuit 21.
D, EID, and an information signal API generated by the information signal generation circuit 22 are supplied. The above identification signal generation circuit 2
1 generates a start identification signal SID and an end identification signal RID in synchronization with the audio signal being read out from the memory device W14. The start and end identification signals SID and BID are recorded on the recording disc Dc together with the audio signal AS, and are used to indicate the start and end of the recording position of the audio signal AS, respectively, on the recording disc Dc. The information signal generation circuit 22 is
A predetermined control signal is supplied from the system controller 23, and the information signal API is generated. This information signal AP
I is the recording disk D0 along with the audio signal As.
This is a signal for controlling the operation of the reproducing device when reproducing the audio signal AS recorded on the recording disk D0.

The signal output from the adder 20 is the 7th U! J
As shown in , the start identification signal SID and the information signal A
The signals are arranged in the following order: PI, the audio signal AS which has been subjected to the pre-emphasis processing and time axis compression, and the end identification signal ED. The length of the signals arranged in this manner is determined by the length of time 1.1, which corresponds to the length of the segment in which the signals are recorded, on the magnetic disk Dc. It is within.

In the signal output from the adder 20, the pre-emphasis process is applied only to the audio signal As, and not to the identification signals SID, EID, which are the control information signals, and the information signal AIP. That is, each of the control information signals described above is subjected to FM modulation in its generated state. Here, each of the control information signals described above is a digital signal, and there is little need to consider the so-called S/N ratio in recording and reproducing digital signals, so there is no problem even if pre-emphasis processing is not performed.

The information signal API is composed of, for example, 64 bits, and is composed of data such as a track address, a continuous audio start address, a continuous audio succeeding address, and a time axis compression rate mode. The track address data indicates the absolute address on the recording disc 0 where the signal is recorded.

The continuous audio start address data indicates the start trunk address when a continuous series of audio is recorded over multiple recording tracks on the recording disk 0. The data of the 0 time axis compression mode in which the track address where the audio signal is recorded is indicated by the data of the continuous audio succeeding address indicates the compression ratio (for example, 1/640) of the recorded audio signal.

The output signal of the adder 20 is sent to a D/A converter (digital/analog converter) 24. This D/A
The converter 24 performs D/AI conversion on the signal sent from the adder 20 based on the readout control signal supplied from the second oscillator 16, and converts the output signal of this D/A converter 24. , a low-pass filter 25 for noise reduction, an amplitude limiter 26 for limiting signals exceeding a predetermined amplitude, and the video/audio changeover switch 4.
The signal is sent to the FM modulation circuit 5 via the FM modulation circuit 5.

This FM modulation circuit 5 modulates the sent audio signal into an FM signal and sends it to the recording head 6. This recording head 6
records the sent signal corresponding to a predetermined segment on the recording disk Dc.

As described above, in the audio signal recording circuit according to the present invention, pre-emphasis processing is performed on a digital signal whose transmission speed is low before time-base compression is performed. It is extremely difficult to perform pre-emphasis processing on a digital signal having a high transmission rate after it has been subjected to 0-time axis compression processing that can be pre-emphasized by the pre-emphasis circuit 12.

Note that it is also possible to perform pre-emphasis processing using an analog circuit on the analog signal before time-base compression processing and before further digital conversion, but in this case, when changing the compression ratio, In the pre-emphasis circuit 12 in the audio signal recording circuit according to the present invention, where it is difficult to change circuit characteristics such as constants, the characteristics of the pre-emphasis circuit 12 are automatically changed as the compression ratio is changed. It can be easily configured to

In order to reproduce the audio signal recorded by the audio signal recording circuit according to the present invention configured as described above, as shown in FIG. The FM demodulation circuit 28 demodulates the signal.

The signal demodulated by this FM demodulation circuit 28 is sent to an A/D converter 30 via a low-pass filter 29 and digitally converted. Then, the audio signal AS is extracted based on the start identification signal SID, the information signal API, and the end identification signal BID, and is sequentially written into the memory device 31. The signal AS is sequentially outputted from the memory device 31 based on the reciprocal of the compression ratio, thereby expanding the time axis.

The time-base expanded audio signal is sent to a de-emphasis circuit 33 via a low-pass filter 32. The de-emphasis circuit 33 is a circuit that performs de-emphasis processing on the signal to be sent, and is composed of a plurality of multipliers and delay circuits like the pre-emphasis circuit 12 described above.

The de-emphasis processing is a reverse process of the pre-emphasis processing, and the coefficients in each multiplier and the delay time in each delay circuit constituting the de-emphasis circuit 33 are set to values different from each numerical value in the pre-emphasis circuit 12. This can be done by setting .

The de-emphasized audio signal is converted into analog by a D/A converter 34 and sent to an expander 36 via a low-pass filter 35. This expander 36 converts the signal sent to the compressor 8
The amplitude is expanded based on the reciprocal of the amplitude compression rate in , and the signal is sent to the audio signal output terminal 37. In this way, the audio signal can be reproduced.

Effects of the H0 Invention As described above, the audio signal recording circuit according to the present invention uses a digital circuit to perform pre-emphasis processing on the audio signal after digital conversion but before time axis compression. are giving.

Therefore, the accuracy and stability of the pre-emphasis processing are extremely less affected by the accuracy of the circuit components and the temperature and humidity, and the pre-emphasis processing can be performed with high accuracy and excellent stability. Further, since processing is performed on a signal whose transmission speed is low before being time-base compressed, the configuration of a circuit that performs pre-emphasis processing can be simplified.

Furthermore, pre-emphasis processing is not performed on the identification control information signal that is added to the audio signal after time axis compression.

That is, the present invention improves the accuracy and stability of pre-emphasis processing, and also allows the control information signal to be recorded together with the audio signal when recording the audio signal to be accurately recorded. By reproducing the audio signal, it is possible to provide an audio signal recording circuit that can accurately reproduce the audio signal.

[Brief explanation of the drawing]

The first leap is a block diagram showing the configuration of an audio signal recording circuit according to the present invention, FIG. 2 is a circuit diagram showing an example of the configuration of a pre-emphasis circuit constituting the audio signal recording circuit, and FIG. is a graph showing the frequency characteristics of the pre-emphasis circuit. FIG. 4 is a plan view schematically showing the shape of a magnetic disk on which audio signals are recorded by the audio signal recording circuit;
FIG. 5 is a block diagram showing an example of the configuration of a circuit for reproducing audio signals recorded by the audio signal recording circuit. FIG. 6 is a block diagram showing the configuration of a conventional audio signal recording circuit, FIG. 7 is a schematic diagram showing the configuration of an audio signal recorded by the conventional audio signal recording circuit, and FIG. 8 is a block diagram showing the configuration of a conventional audio signal recording circuit. FIG. 2 is a schematic diagram illustrating the configuration of an audio signal recorded by an audio signal recording circuit, and the state after pre-emphasis processing. 5...FM modulation circuit 10...A/D converter 12...
......Pre-emphasis circuit 14...
...Memory device 20...Adder

Claims (1)

[Scope of Claims] An analog/digital converter that digitally converts an input analog audio signal; a pre-emphasis circuit that performs pre-emphasis processing on a digital audio signal output from the analog/digital converter; a time-base compression circuit that performs time-base compression processing on the processed digital audio signal; an adder that adds a control information signal to the digital audio signal output from the time-base compression circuit; and a control information signal that is output from the adder. An audio signal recording circuit comprising a digital/analog converter that converts a signal into analog, and a modulator that frequency modulates the analog audio signal output from the digital/analog converter.