JPH09223354A - Audio device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an audio device capable of digitally and precisely recording analog sound. SOLUTION: An analog sound signal outputted from an FM radio receiving part 2 is converted into a digital signal SD by an A/D converter 6 to be filter- processed by a digital BPF in a DSP(digital signal processor) circuit 7. A microcomputer 8 changes the coefficient of the digital BPF according to a mode signal SFM, and since it controls so that such a steep digital filter processing that only the digital signal of a frequency band of an applied band 30Hz-15kHz of an FM radio broadcasting is outputted, is performed, a frequency component excepting 30Hz-15kHz isn't outputted from the DSP circuit 7. Then, the number of bits for coding processing of the sound signal of the applied band are increased since the necessity that a noise signal excepting the applied band is eliminated in the coding processing in an MD(MiniDisk) signal processing circuit 9. Thus, a regenerative sound recorded on the MD in an MD recording/ reproducing part 5 becomes of high-fidelity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio device. More specifically, the input analog signal is subjected to the process of extracting only the signal in the frequency band used and digitally recorded on the recording medium, so that the reproduced sound quality is deteriorated due to the recording of the signal (noise component) outside the frequency band used. It is an improved one.

[0002]

2. Description of the Related Art Audio reproduced from a cassette tape and analog audio such as FM radio broadcast and AM radio broadcast are supplied to a mini disk (hereinafter referred to as "MD") player or a digital compact cassette (hereinafter referred to as "DCC") player. May be recorded on digital audio equipment.

These analog audio signals are converted into digital signals by an A / D converter built in a digital audio device and then digitally recorded on a recording medium such as MD or DCC.

[0004]

By the way, in a digital audio device such as a CD player or a DCC player, as shown in FIG. 3A, about 20 Hz to about 22 KH.
Although audio in the z band can be recorded, the frequency band of analog audio output from a cassette reproducing device or a radio receiver is generally narrower than the recordable band of a digital audio device. For example, the frequency band used for FM radio broadcasting is about 30 Hz to 15 KHz, and the 19 KHz pilot signal is subjected to low-pass filtering at the time of reception so as not to be output.

However, this low-pass filter is an analog filter and has frequency characteristics such that the cut-off frequency is 15 KHz as shown in FIG. 3 (b).

Since this filter characteristic is not sharply band-limited, the filter output is slightly output even at a frequency of 15 KHz or higher as shown in FIG. 3 (c). Since the audio signal is not included in the high frequency band of 15 KHz or higher, it becomes a noise component. In addition to this, white noise (hatched line) is also included. In addition, since no filter is used in the low frequency band, noise components existing below 30 Hz are also output, and in the case of a digital audio device using MD, DCC, etc., audio compression encoding processing according to the recording medium used. Is done. As is well known, M
In D, ATRAC (Adaptive TRansform Acoustic Codi
ng) processing, DCC in PASC (Precision Adaptive S
ub-band Coding)) processing. Use band 30Hz-1
Since noise components (including white noise) mixed in 5 KHz are masked by a high-level audio signal, these noise components are not recorded on the recording medium.

However, the frequency component (2
Noise components having a level above the minimum audible limit due to each audio compression coding process in 0 Hz to 30 Hz and 15 KHz to 22 KHz) are recorded on the recording medium.
In particular, the residual component of the pilot signal is also recorded because it has a relatively high level.

[0008] Similarly, AM radio broadcasting having a use band of about 100 Hz to about 6 KHz and about 20 Hz to 10 KHz
Even with a cassette tape (or 20 Hz to 20 KHz) (the upper limit of the frequency varies depending on the type of tape, etc.), a steep filter is generally not used as a band limiting filter. Therefore, the audio signal output from each device often includes noise components in the low frequency band below the lower limit frequency and the high frequency band above the upper limit frequency. If this is recorded on a digital audio device, it will be
A noise component (high frequency noise) having a level up to Hz and an upper limit frequency up to 22 KHz and above the minimum audible limit is also recorded on the recording medium together with the audio signal.

The dynamic range of digital audio equipment is generally much wider than that of analog audio equipment. For example, the dynamic range of MD equipment is 96d.
Since it is about B, the above high frequency noise is also reproduced. This reproduction noise on the high frequency side causes deterioration of reproduction sound quality.

Further, in the voice compression encoding process in the digital equipment, a band (20 Hz to 30 H) other than the voice band to be originally processed (for example, 30 Hz to 15 KHz in FM voice) is used.
z and 15 KHz to 22 KHz) existing components (FM
All the noise components to the voice) must be compressed and encoded. Therefore, the encoding amount (the number of bits) that should be assigned to the original audio signal decreases, and the dynamic range of the audio signal becomes narrow. That is, the performance of the digital audio device cannot be maximized.

Therefore, the present invention provides an audio apparatus capable of improving reproduced sound quality by blocking (cutting) noise components in unnecessary frequency bands other than the used band of analog voice when input analog voice is digitally recorded. It is provided.

[0012]

An audio device according to the present invention has an A / D converter for converting an analog audio signal into a digital signal, and an A / D converter having only a component of a frequency band used for the analog audio signal. A frequency characteristic adjusting unit that sharply limits the frequency characteristic of the digital signal output from the converter, a digital signal processing unit that encodes the digital signal output from the frequency characteristic adjusting unit, and an output of the digital signal processing unit. And a digital recording section for performing digital recording on a recording medium.

The analog audio signal is converted into a digital signal by the A / D converter and outputted, and the frequency characteristic adjusting means adjusts the used frequency band of the input signal to its pass band. Then, it is encoded by the digital signal processing unit and digitally recorded by the digital signal processing unit. Therefore, in the digital signal processing unit, it is not necessary to perform the encoding process on the signal other than the band used for the input signal,
Therefore, the resolution of the encoding process for the input signal can be increased. Therefore, the reproduced sound quality is significantly improved, and high-fidelity digital recording becomes possible.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION An audio apparatus 100 as an embodiment of the present invention will be described below with reference to the drawings. This audio device 100 is for recording / reproducing cassette tapes, receiving AM / FM radio broadcasts, and C
It is an audio device (so-called mini component system) capable of reproducing D and recording / reproducing MD.

In FIG. 1, the audio device 100 is
Cassette tape recording / reproducing unit 1, FM radio receiving unit 2, A
M radio receiving unit 3, CD reproducing unit 4, and MD recording / reproducing unit 5
Having.

The cassette tape recording / reproducing unit 1 records / reproduces a cassette tape and outputs an analog audio signal. In the FM radio receiving section 2 and the AM radio receiving section 3,
FM radio broadcasting and AM radio broadcasting are respectively received and their analog audio signals are output. CD playback unit 4
Then, the CD is reproduced and the digital audio signal is output. In the MD recording / reproducing unit 5, the M of audio data is
Recording and reproduction on D are performed.

The audio device 100 further includes an A / D converter 6, a digital signal processor circuit (hereinafter,
It has a "DSP circuit") 7, a microcomputer 8 and an MD signal processing circuit 9.

A cassette tape or A
When recording the sound of the M / FM radio broadcast on the MD by the MD recording / reproducing unit 5, the analog audio signal SA output from the cassette tape recording / reproducing unit 1, the FM radio receiving unit 2 and the AM radio receiving unit 3 is A / It is supplied to the D converter 6 and converted into the digital audio signal SD.

A digital audio signal SD output from the A / D converter 6 is supplied to the DSP circuit 7. DS
The P circuit 7 is configured as a digital band pass filter (hereinafter referred to as "digital BPF") capable of changing the filter characteristic, and the frequency band of the digital audio signal SD is limited as desired.

When the audio of the cassette tape is recorded on the MD by the user's operation, the cassette tape reproducing section 1
The mode signal STA is supplied to the microcomputer 8. F
When recording the sound of the M radio broadcast or the sound of the AM radio broadcast on the MD, the mode signals SFM and SAM are supplied to the microcomputer 8 from the FM radio receiving unit 2 and the AM radio receiving unit 3, respectively. The microcomputer 8 identifies each mode signal, and the digital B of the DSP circuit 7 is identified according to the identified mode.
Control the coefficient of PF. By this coefficient control, the used frequency band of the input audio signal itself is set as its pass band. In FM broadcasting, its pass band is 30H
z to 15 KHz, AM broadcasting 100 Hz to 6 K
Hz becomes the pass band, and 20 Hz for cassette tape
Coefficient control is performed so that 100 KHz (20 Hz to 20 KHz) becomes the pass band. Since there is a digital filter, the pass band can be set to have steep characteristics.

The MD signal processing circuit 9 includes a digital audio signal S band-limited by the digital filter of the DSP circuit 7.
A DS is supplied, and ATRAC audio compression encoding is performed.
Encoding processing for error correction processing is performed, and modulation processing is performed. The recording audio data output from the MD signal processing circuit 9 is supplied to the MD recording / reproducing unit 5. As a result, the recording audio data of the cassette tape, FM radio, AM radio, etc. is magnetic field modulated recorded on the MD.

When the sound reproduced by the CD reproducing section 4 is recorded in the MD by the user's operation, since the reproduced sound signal SCD is a digital signal, it does not go through the A / D converter 6 and the DSP circuit 7. It is directly supplied to the MD signal processing circuit 9.

Next, the reproducing system will be described. The audio device 100 has a D / A converter 10, a power amplifier 11, and a speaker 12 as a reproduction system. The reproduced audio data reproduced by the MD recording / reproducing unit 5 is supplied to the MD signal processing circuit 9 for demodulation processing, decoding processing for error correction processing, and decompression decoding of error-corrected compressed coded data. Processing is performed.

The digital audio signal decoded by the MD signal processing circuit 9 is supplied to the D / A converter 10 and converted into an analog audio signal. An analog audio signal is supplied from the D / A converter 10 to the power amplifier 11 and amplified. Then, the sound is output from the speaker 12.

In the above configuration, the FM radio receiving section 2
The operation of recording the sound of the FM radio broadcast received in step 3 on the MD by the MD recording / reproducing unit 5 will be described with reference to FIGS. 1 and 2.

When the sound of the FM radio broadcast received by the FM radio receiving unit 2 is recorded on the MD by the MD recording / reproducing unit 5 by the user's operation, the output signal SA of the FM radio receiving unit 2 is A / D converter. 6 is supplied. This F
As shown in FIG. 2A, the M radio signal SA is an audio signal having a noise component other than the used frequency band of 30 Hz to 15 KHz. The FM radio signal SA is converted into a digital signal SD by the A / D converter 6 and output.
As shown in FIG. 2B, this digital signal SD is also 30
It has low frequency components below Hz and high frequency components above 15 KHz.

The FM radio receiving section 2 outputs to the microcomputer 8 a mode signal SFM for identifying that the sound to be recorded on the MD is output from the FM radio receiving section 2. When the mode signal SFM is supplied, the microcomputer 8 changes the coefficient of the digital BPF of the DSP circuit 7 under the control of an algorithm according to the mode (FM mode). The filter characteristic of the DSP circuit 7 at this time is a steep filter characteristic, as shown in FIG.
As shown in, the lower limit frequency 30 Hz and the upper limit frequency 15
The cutoff is sharp at KHz. This allows the DSP
The digital audio signal SDS output from the circuit 7 is as shown in FIG.
As shown in (d), frequencies below 30 Hz and 15K
The digital signal does not include noise components in the number of frequency bands above Hz.

In the MD signal processing circuit 9, as shown in FIG. 2 (e), voice compression coding processing is performed on the signal components in the frequency band of 20 Hz to 22 KHz which can be recorded in the MD. The digital audio signal SDS is 3
It is a frequency component from 0 Hz to 15 KHz. Therefore,
As shown in FIG. 2 (f), encoding processing for signals in the frequency band of 20 Hz to 30 Hz and 15 KHz to 2
The encoding process for the signal in the frequency band of 2 KHz is not performed, and the number of allocated bits for the voice signal of 30 Hz to 15 KHz increases accordingly.

As a result, unnecessary noise components are not reproduced, so that the reproduced sound quality can be greatly improved.

Even when the audio of the cassette tape or the audio of the AM radio broadcast received by the AM radio receiving section 3 is recorded in the MD, only the digital audio signal SDS in the frequency band used in each mode is sent to the MD signal processing circuit 9. As supplied, the coefficient of the digital BPF of the DSP circuit 7 is controlled. As a result, similarly to the case of recording the FM radio broadcast sound, only the signal in the used frequency band is recorded, so that high-fidelity reproduced sound quality can be enjoyed.

Incidentally, in the above-mentioned embodiment,
When the audio reproduced by the cassette tape recording / reproducing unit 1 is recorded on the MD by the MD recording unit 5, the coefficient of the digital BPF of the DSP circuit 7 is uniformly changed to perform the filtering process. A mode signal for identifying the type is supplied to the microcomputer 8 from the cassette tape recording / reproducing unit 1, and the digital BPF of the DSP circuit 7 is controlled by the microcomputer 8 which identifies the type of the cassette tape by the mode signal. The coefficient may be changed. For example, the upper limit frequency for cutting with digital BPF is 15K for normal tape.
Hz, and 16 KHz for chrome tape.

Further, in the above-mentioned embodiment,
The case where the analog sound on the reproducing side is the output sound of the AM / FM radio or the reproduced sound of the cassette tape is shown, but the present invention can be applied to other analog sound. Further, the recording side is not limited to the MD, but the present invention is applied to other recordable digital devices such as DCC and DAT.

[0033]

According to the present invention, the input analog audio signal is converted into a digital signal by the A / D converter and output to the digital filter. Then, according to the mode identified by the mode identifying unit, the coefficient of the digital filter is controlled so that only the frequency signal in the used frequency band is output. As a result, the digital signal processing unit does not need to perform the encoding process of the frequency components other than the used band, and the number of bits can be allocated to the encoding process of the audio signal of the used band. Therefore, in the present invention, the noise component outside the used band is cut, so that the reproduction noise is reduced, and a remarkable effect that a high-fidelity reproduced sound can be realized is achieved.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an audio device 100 as an embodiment of a disc device according to the present invention.

2 is a diagram showing input / output signals and the like of each unit of the audio device 100. FIG.

FIG. 3 is a diagram showing a frequency band used for FM radio output.

[Explanation of symbols]

 1 cassette tape recording / reproducing section 2 FM radio receiving section 3 AM radio receiving section 4 CD reproducing section 5 MD recording / reproducing section 6 A / D converter 7 digital signal processor circuit 8 microcomputer 9 MD signal processing circuit 10 D / A converter 11 power amplifier 12 speaker 100 audio device

Claims (2)

[Claims] 1. An A / D converter for converting an analog audio signal into a digital signal, and a frequency of the digital signal output from the A / D converter so as to have only a component of a frequency band used for the analog audio signal. A frequency characteristic adjusting unit for sharply band limiting the characteristic, a digital signal processing unit for encoding the digital signal output from the frequency characteristic adjusting unit, and a digital unit for digitally recording the output of the digital signal processing unit on a recording medium. An audio device having a recording unit. 2. The adjusting means includes a mode identifying means for identifying an input analog audio signal, a digital filter, and a digital signal output from the digital filter.
2. The audio apparatus according to claim 1, further comprising control means for controlling the coefficient of the digital filter so as to have only the component of the used band of the analog audio signal identified by the mode identifying means.