JP2644508B2 - Audio recording device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an audio recording apparatus which compresses an audio signal on a time axis and records it on a recording medium.

2. Description of the Related Art Conventionally, there has been known an electronic still video system in which a still image is recorded or reproduced on a magnetic disk called video floppy. According to this still video system, not only a still image but also an audio signal can be recorded or reproduced on a video signal track by compressing the time axis. FIG. 4 is a block diagram showing the configuration of an audio signal recording / reproducing apparatus of this type of still video system.

In FIG. 1, reference numeral 1 denotes an input terminal, and 2 denotes a low-pass filter for applying a band limitation to an audio signal input from the input terminal 1 so as not to generate aliasing noise at the time of A / D and D / A conversion described later. Reference numeral 3 denotes an amplitude compression circuit (hereinafter referred to as an NR circuit) for performing noise reduction. 4 denotes an A / D converter for converting an analog audio signal output from the NR circuit 4 into a digital signal at a predetermined rate; Is a time axis compression / expansion circuit for the audio signal converted into a digital signal by the A / D converter 4. The time axis compression / expansion circuit includes, for example, a memory, and stores a digital audio signal in the memory, and when reading from the memory, varies the clock for reading, thereby compressing and expanding the time axis of the signal. Reference numeral 6 denotes a D / A conversion circuit for converting the time-axis-compressed digital signal output from the time-axis compression / expansion circuit 5 into an analog signal;
Is a pre-emphasis circuit that emphasizes the high frequency range of the signal to improve S / N, 8 is a clip circuit that clips the high frequency side of the signal at a predetermined level, and 9 is an FM modulation that FM-modulates a time-axis-compressed analog audio signal. Vessel, 10 is a recording amplifier, 11 is a recording,
A reproduction switching switch 12 is a magnetic head for recording and reproducing data on and from a magnetic disk (not shown). A recording system is configured by the above configuration.

Next, the reproduction system will be described. In FIG. 1, reference numeral 13 denotes a reproduction amplifier for amplifying a reproduction signal read from a magnetic head 12 on a magnetic disk to a predetermined level, and reference numeral 14 denotes an FM input through the reproduction amplifier 13. FM demodulator that demodulates the modulated analog playback signal, 15 is a de-emphasis circuit that gives the de-emphasis characteristic of the inverse characteristic to the pre-emphasis characteristic applied at the time of recording to the FM demodulated audio signal and returns to the original signal characteristic, and 16 is An analog-to-digital (A / D) conversion circuit that converts an analog audio signal input through the de-emphasis circuit 15 into a digital signal and inputs the digital signal to the time axis compression / expansion circuit 5. Here, when the time-axis-compressed signal is expanded on the time axis and converted to the original time axis, the A / D-converted digital audio signal is stored in the memory of the time-axis compression / expansion circuit 5, and the signal is transmitted from the memory. The time axis can be expanded by changing the read clock when reading data. 17 is a D / A converter for converting a signal expanded on the original time axis by the time axis compression / expansion circuit 5 into an analog signal, 18 is an amplitude expansion circuit for expanding the amplitude for performing noise reduction, and 19 is an output terminal. is there.

In the figure, at the time of recording, an audio signal input from an input terminal 1 is band-limited by a low-pass filter 2 and then compressed by an NR compression circuit 3 so that, for example, when the amplitude is logarithmic, it becomes 1/2. . Then, after performing A / D conversion by the A / D converter 4, the signal is input to the time axis compression / expansion circuit 5, and is 320 ×, 640 ×, 1280 × specified by the unified format of the still video system. Time axis compression is performed at any magnification (5 seconds, 10 seconds, and 20 seconds, respectively, as the actual time). The time-axis-compressed signal is converted into an analog signal by a D / A converter 6, given a predetermined emphasis by a pre-emphasis circuit 7, and after a predetermined amplitude limitation by a clipping circuit 8, and then by an FM modulator 9. The signal is FM-modulated and supplied to the recording amplifier 10. In the recording amplifier, power supply amplification is performed, and recording is performed on the magnetic disk by the magnetic head 12 via the switch 11 switched to the recording amplifier side.

FIG. 5 shows signal waveforms at various parts in the circuit configuration of FIG.

FIG. 2A shows a waveform of an audio signal supplied to the input terminal 1.
FIG. 2B shows the output waveform of the D / A converter 6, FIG. 2C shows the signal waveform in which a high frequency portion is emphasized by the pre-emphasis circuit 7, and FIG. 5 shows signal waveforms in a restricted state.

Accordingly, the signal waveform input to the FM modulator 9 has a shape as shown in FIG.

It should be noted that the original signals shown in FIG.
Is compressed on the time axis, so the position of each waveform on the time axis is different.

In the case of reproduction, the switch 11 is switched to the reproduction amplifier 13 side, and the information read by the head 12 is
The signal is supplied to the FM demodulator 14 via the reproduction amplifier 13 and FM-demodulated, and is de-emphasized by the de-emphasis circuit 15. And the day emphasis signal is A / D converter 16,
After being expanded in time axis through the time axis compression / expansion circuit 5 and the D / A converter 17 and converted into the original signal before compression, it is output from the output terminal 19 through the amplitude expansion circuit 18. .

(Problems to be solved by the invention) However, according to the above configuration, FIG.
As is apparent from the signal waveform of (d), after the A / D conversion, the waveform is pre-emphasized to emphasize the high frequencies and the clip is performed. FIG. 5 (d) because the amplitude is limited by clipping.
As shown in (1), a part of the A / D-converted signal is discarded after its amplitude is limited, so that the dynamic range in the A / D conversion cannot be used effectively and quantization noise becomes a problem. Therefore, there has been a demand for a method capable of solving the problem and effectively using the dynamic range.

The present invention has been made in order to solve the above-described problems, and to effectively use the dynamic range of A / D conversion and D / A conversion performed when converting the time axis of an audio signal over the entire area. By reducing quantization noise, the A / A
An object of the present invention is to provide an audio recording device capable of performing D conversion and D / A conversion.

(Means for Solving the Problems) In order to achieve the above-mentioned object, an audio recording apparatus of the present invention compresses an audio signal on a time axis, and then modulates the frequency of the audio signal to record the audio signal on a recording medium. A pre-emphasis means for performing an emphasis process for emphasizing a predetermined frequency component on the input and input audio signal and outputting the same, and an amplitude of the audio signal on which the predetermined frequency component output from the pre-emphasis means is emphasized. And an analog / digital conversion means for converting an audio signal output from the amplitude limiting means whose amplitude is limited to a predetermined range into a digital signal and outputting the digital signal. Time axis compression processing means for performing time axis compression processing on the digital signal output from the analog / digital conversion means and outputting the digital signal; Digital / analog converting means for converting a digital signal output from the interaxial compression processing means into an analog signal and outputting the same, and recording means for frequency-modulating the signal output from the digital / analog converting means and recording the same on a recording medium It is provided with.

(Operation) According to the above configuration, the audio signal is pre-emphasized, A / D converted, and the signal after the A / D conversion is subjected to high frequency emphasis. Quantization noise can be reduced without being subjected to amplitude limitation or the like.

(Example) Hereinafter, the audio recording device of the present invention will be described with reference to the drawings.
One embodiment will be described in detail.

FIG. 1 is a block diagram showing a first embodiment of the voice recording apparatus of the present invention. In the figure, the same components as those of the conventional example shown in FIG. 4 are denoted by the same reference numerals, and the description thereof will be omitted.

In this embodiment, the difference from the configuration of FIG.
In the prior art shown in FIG. 4, the pre-emphasis circuit and the clip circuit, which are sequentially arranged in the recording system at the next stage of the D / A converter 6, are removed, and the circuit between the NR compression circuit 3 and the A / D conversion circuit 4 is removed. In addition, the pre-emphasis circuit of the characteristics specified in the format of the still video system
20, the clipping circuit 21 is provided, and the de-emphasis circuit 15 disposed between the FM demodulator 14 and the A / D conversion circuit 16 in the reproduction system is removed, and the D / A converter 17 is provided.
And the NR expansion circuit 18 as a de-emphasis circuit 22.

Therefore, according to the configuration of the present embodiment, the analog audio signal input from the input terminal 1 is band-limited by the low-pass filter 2 according to the time axis compression ratio, and then the NR compression circuit 3
The amplitude is then compressed and supplied to the pre-emphasis circuit 20. The high-frequency component of the audio signal supplied to the pre-emphasis circuit 20 is emphasized, the amplitude of the audio signal is limited to a predetermined level by a clipping circuit 21, and then supplied to the A / D converter 4, where the digital signal is digitalized based on a predetermined clock. Converted to a signal. At this time, A / D conversion is performed after high-frequency emphasis and amplitude limitation, so that the signal after A / D and D / A conversion is amplitude-limited, and consequently the dynamic range may be narrowed. In addition, the dynamic range of the A / D converter can be fully used. In other words, D /
When pre-emphasis is applied after A conversion and the amplitude is limited, D
Since the amplitude of the / A-converted signal is limited, in other words, the limited signal is also subjected to A / D and D / A conversion, and the dynamic range in A / D conversion is effectively enabled. It cannot be used.

The A / D-converted signal is time-axis-compressed by a time-axis compression circuit 5 at a predetermined compression ratio, and then converted to a time-axis-compressed analog signal by a D / A converter 6. The analog signal is supplied to an FM modulator 9 where it is FM-modulated and converted into an FM-modulated signal in a video band. After that, the analog signal is transmitted via a recording amplifier 10, a recording / reproduction switching switch 11, and a magnetic head 12 to a magnetic disk (not shown). Recorded in the upper track.

At the time of reproduction, the reproduced audio signal is a magnetic head.
12, supplied to the FM demodulator 14 via the reproduction amplifier 13,
Demodulated. The FM-demodulated signal is converted into a digital signal by an A / D conversion circuit 16 and then input to a time axis compression / expansion circuit 5 where the signal is expanded on a time axis, and supplied to a D / A conversion circuit 17 to be time-scaled. Is converted into an analog signal converted back to the original signal. Then, the output of the D / A conversion circuit is supplied to a de-emphasis circuit 22, where the pre-emphasis is performed at the time of recording and the de-emphasis is performed with the opposite characteristic when the high frequency is emphasized. Output from 19.

Here, the above-described signal processing will be described in more detail with reference to FIG.

2 shows signal waveforms at various points in the block diagram of FIG. 1. FIG. 2 (a) shows a waveform of an audio signal inputted from the input terminal 1, and FIG. 2 (b) shows a waveform obtained by the pre-emphasis circuit 20. FIG. 3C shows a signal waveform whose amplitude is limited by the clipping circuit 21, and FIG. 4D shows a signal waveform outputted through the A / D conversion circuit 4 and the time axis compression circuit 5. 5 shows signal waveforms output from the / A conversion circuit 6. Since the time axis of the waveform of FIG. 9D is compressed, the waveform is compressed in the horizontal axis direction in FIGS. According to this embodiment, before the audio input signal is A / D-converted by the A / D conversion circuit 4, the high-frequency emphasis is performed through the pre-emphasis circuit 20 and the amplitude is limited by the clip circuit 21, so that the A / D, The signal after D / A conversion is supplied to the FM modulator 9 as it is without being subjected to amplitude limitation or the like, and is subjected to FM modulation. Therefore, the number of bits of the A / D and D / A converters is limited, especially when there is no room for the number of bits.
It is possible to solve the conventional disadvantage that the dynamic range is reduced by limiting the amplitude of the signal after A / D and D / A conversion, and it is possible to effectively use the dynamic range in A / D conversion. it can. As a result, quantization noise is reduced, and a low-noise, Hi-Fi audio signal processing system can be realized.

According to the waveform diagram, according to the conventional device, since the high frequency range is emphasized after the D / A conversion and the amplitude is limited, a part of the D / A converted signal is cut. According to the signal waveform of FIG. 3 (d), the waveform after D / A conversion is output without any amplitude limitation or the like, and it can be seen that the dynamic range is fully used.

According to this embodiment, the above-described functions can be obtained without increasing the number of circuit components as compared with the conventional example, which is also advantageous in terms of cost.

FIG. 3 is a block diagram showing another embodiment of the present invention.

In the figure, the same components as those of the first embodiment of the present invention shown in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.

According to the present embodiment, before the audio signal input from the input terminal 1 is supplied to the A / D converter 4, the high frequency emphasis and the amplitude limit are performed by the pre-emphasis circuit 23 and the clip circuit 21, respectively. / D conversion, time axis compression, D / A
Before performing FM modulation after conversion, pre-emphasis circuit
After returning the signal emphasized in the high frequency range by the de-emphasis circuit 24 having the opposite characteristic to that of the original signal, the high frequency range is again emphasized by the pre-emphasis circuit 20 having the emphasis characteristic similar to the format in the still video system, and then the FM The signal is FM-modulated by the converter 9 and recorded on a recording medium (not shown) via the recording amplifier 10 and the head 12.

In the reproduction system, the reproduction signal supplied to the FM demodulator 14 via the head 12 and the reproduction amplifier 13 is supplied to a de-emphasis circuit 22 having a reverse characteristic of the pre-emphasis circuit 20 according to the pre-emphasis characteristic of the still video format. After being supplied, the pre-emphasis circuit 25 applies pre-emphasis and then returns to the analog audio signal expanded on the original time axis via the A / D converter 16, the time axis compression / expansion circuit 5, and the D / A conversion circuit 17. After that, the emphasized high-frequency component is returned to the original signal via the pre-emphasis circuit 25 and the de-emphasis circuit 26 having the opposite characteristic, and then the amplitude compressed by the amplitude expansion circuit 18 is returned to the original amplitude characteristic. Are output from the output terminal 19.

According to the above-described embodiment, the pre-emphasis circuit and the de-emphasis circuit 23 before and after A / D and D / A conversion
26 and the pre-emphasis circuit and the de-emphasis circuit 20, 22 determined in the still video format can be set separately, so that the pre-emphasis circuit and the de-emphasis circuit 22 to 25 separately from the formatted emphasis characteristic, The pre-emphasis and de-emphasis characteristics can be set so that the effect of reducing the quantization noise by the A / D conversion is optimized.

(Effect of the Invention) As described above, according to the audio recording device of the present invention,
When converting the time axis of an audio signal, in the amplitude limitation performed after the A / D conversion and the D / A conversion processing, an increase in quantization noise due to loss of a part of the signal after the D / A conversion , The dynamic range in the A / D conversion and the D / A conversion can be effectively used over the entire range, and the quantization noise in the high range of the audio signal can be significantly reduced.

Further, according to the audio signal recording device of the present invention, the A / D
Since the dynamic range in the conversion and the D / A conversion can be effectively used over the entire area, it is extremely effective when the number of quantization bits in the A / D conversion and the D / A conversion is limited.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of an audio recording apparatus according to the present invention, and FIGS. 2 (a) to 2 (d) are waveform diagrams showing signal waveforms at various parts in the block diagram of FIG. FIG. 3 is a block diagram showing a second embodiment of the audio recording apparatus according to the present invention, FIG. 4 is a block diagram showing an example of a conventional apparatus, and FIGS. 5 (a) to 5 (d) are block diagrams. FIG. 5 is a waveform diagram showing signal waveforms of various parts in the conventional example of FIG. DESCRIPTION OF SYMBOLS 1 ... Input terminal 2 ... Low-pass filter 3 ... Amplitude compression circuit 4,16 ... A / D converter 5 ... Time axis compression / expansion circuit 6,17 ... D / A conversion circuit 9 ... FM modulator 10 Recording amplifier 11 Recording / reproduction switching switch 12 Head 13 Reproduction amplifier 14 FM demodulator 18 Amplitude expansion circuit 19 Output terminals 20, 23, 25 Pre-emphasis circuit 21 Clip circuit 22,24,26 …… Day emphasis circuit

Claims (1)

(57) [Claims] 1. An apparatus for compressing a time axis of an audio signal, frequency-modulating the signal, and recording the signal on a recording medium, comprising the steps of: inputting the audio signal; and emphasizing a predetermined frequency component with respect to the input audio signal. Pre-emphasis means for applying and outputting; a predetermined frequency component output from the pre-emphasis means for limiting the amplitude of the emphasized audio signal to within a predetermined range; and outputting the amplitude limit means; and An analog-to-digital converter for converting an output audio signal having a limited amplitude within a predetermined range into a digital signal and outputting the digital signal; and performing a time axis compression process on the digital signal output from the analog / digital converter. Applying and outputting a time axis compression processing means, and converting a digital signal output from the time axis compression processing means into an analog signal A digital / analog converting means for outputting, the digital / signal output from the analog conversion means to frequency modulation, sound recording apparatus comprising the recording means for recording on a recording medium.