JPH0575366A - Signal processing circuit in audio equipment - Google Patents

Abstract

PURPOSE:To provide the signal processing circuit in which predetermined processing is implemented regardless of the presence of emphasis in an input signal with respect to the signal processing circuit which applies a prescribed signal processing in response to a signal level of the input signal such as compressor, limiter and expander in the audio equipment. CONSTITUTION:The signal processing circuit controlling variably the signal processing of a signal processing section 1 in response to a signal level of an input signal detected by an input signal level detection section 4 is provided with an emphasis detection section 5 detecting the presence of a pre-emphasis of the input signal and with an emphasis correction section 3 applying de- emphasis to the input signal based on an emphasis presence signal outputted from the emphasis detection section. An output signal of the emphasis correction section is used for an input signal of the input signal level detection section.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal processing circuit, such as a compressor, a limiter, and an expander in an audio device, which performs predetermined signal processing according to the signal level of an input signal.

[0002]

2. Description of the Related Art In audio devices such as CD players, DAT (digital audio tape recorders), cassette tape players, and radio tuners, the source contents (classical music, jazz, popular songs, conversations, etc.) to be reproduced are reproduced. Difference, playback environment (indoor, in car,
The listening characteristics of the reproduced sound vary greatly depending on the difference in the train, noise level, etc.).

For example, when playing music in a noisy environment such as in a car or a train, the pianissimo (pp = weakest sound) of the musical sound is hidden by the noise and cannot be heard. If the reproduction volume (gain) of the audio device is increased in order to prevent this, on the contrary, there is a problem that the sound becomes too loud when loud. On the other hand, when the music is played in a place where it is likely to cause a nuisance in the neighborhood, the volume cannot be increased so much, so that details of the entire song at the low sound level are not clear.

In order to eliminate the above-mentioned problems, an audio apparatus has a purpose such as a compressor for compressing the dynamic range of an output signal, a limiter for suppressing the maximum level of the output signal, or an expander for expanding the dynamic range of the output signal. Various corresponding signal processing circuits are provided on the signal line.

FIG. 7 shows an example of a compressor used in a conventional audio device. In the compressor of FIG. 7, the gain of the variable gain control unit 72 provided on the signal line 71 is changed from the dotted line to the solid line as shown in FIG. 8 according to the signal level of the input signal detected by the input signal level detection unit 73. Is variably controlled like.

As described above, by increasing or decreasing the gain according to the signal level of the input signal and compressing the dynamic range of the entire output signal, the volume of the small musical sound is increased so that it is not hidden by noise, and the large musical sound is increased. Reduces the volume so that it doesn't get annoying, so you can clearly reproduce the details of the entire song when it is small, while eliminating the problem when it is loud.

[0007]

The conventional signal processing circuit including the compressor does not take into consideration the presence or absence of emphasis of the input signal, and directly detects the signal level of the input signal. The gain was variably controlled according to the detected signal level.

By the way, depending on the source of music or the like reproduced by the audio device, as shown in FIG. 9, so-called pre-emphasis for emphasizing high frequencies is applied during recording, and so-called de-emphasis having reverse characteristics is applied during reproduction. Thus, there is a device that expands the dynamic range of reproduced sound.

When such a pre-emphasis signal is input, the conventional compressor shown in FIG.
Since the signal level of the pre-emphasis input signal is directly detected as it is and the gain of the variable gain control section 72 is variably controlled, the effect of the compressor changes depending on the presence or absence of emphasis. Such a problem is caused not only by the compressor, but also by other signals such as the limiter shown in FIG. 10 and the expander shown in FIG. 11 which are designed to perform predetermined signal processing on the input signal according to the signal level of the input signal. This is a common problem in processing circuits.

The present invention has been made under such circumstances, and its purpose is to provide a signal capable of performing a predetermined processing operation regardless of whether the input signal is emphasized or not. It is to provide a processing circuit.

[0011]

In order to achieve the above object, the present invention detects a signal level of an input signal and a signal processing section which performs a predetermined signal processing on the input signal according to the signal level of the input signal. In a signal processing circuit, which comprises an input signal level detection unit and variably controls signal processing of the signal processing unit according to the signal level of the input signal detected by the input signal level detection unit, pre-emphasis of the input signal And an emphasis correction unit that deemphasizes an input signal based on an emphasis presence / absence signal output from the emphasis detection unit, and outputs the output signal of the emphasis correction unit to the input signal level. It is adapted to be used as an input signal of the detection section.

[0012]

[Operation] The emphasis detection unit detects the presence / absence of pre-emphasis of the input signal, and supplies the emphasis correction unit with an emphasis presence / absence signal indicating the presence / absence of pre-emphasis.
If the input signal is not pre-emphasized, the emphasis correction section sends it to the input signal level detection section as it is without applying any de-emphasis to the input signal. On the other hand, when the input signal is pre-emphasized, the emphasis correction unit de-emphasizes the input signal, restores the input signal to the original signal, and then sends it to the input signal level detection unit.

The input signal level detection unit detects the signal level of the input signal sent from the emphasis correction unit, and variably controls the signal processing of the signal processing unit according to this signal level. Therefore, in the case of the signal processing circuit of the present invention, even if pre-emphasis is applied, the signal processing unit can be variably controlled according to the signal level of the input signal returned to the original flat frequency characteristic. Regardless of the presence or absence of pre-emphasis, a constant and constant processing effect can be obtained.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of a compressor of a CD player constructed by applying the present invention. In the figure, reference numeral 1 is a variable gain control section that constitutes a signal processing section, and is connected to a signal line 2. The variable gain controller 1 has an input / output characteristic as a compressor as shown in FIG.

Reference numeral 3 denotes an emphasis correction unit, which is, for example, a filter having the de-emphasis characteristic of FIG. 3 which is an inverse characteristic of the pre-emphasis of FIG. 9 applied to the input signal, and is sent from the emphasis detection unit 5. The de-emphasis is performed on the input signal according to the incoming emphasis signal.

An input signal level detector 4 detects the signal level of the input signal sent through the emphasis corrector 3 and sends the detection result to the variable gain controller 1 as a control signal. Is.

Reference numeral 5 denotes an emphasis detection section for detecting the presence or absence of pre-emphasis of the input signal input to the variable gain control section 1. For example, in the case of a CD player, the control bit of the Q channel of the subcode in the reproduced CD signal. (4 bits) is input, and it is detected from the set state of the control bit whether or not the input signal is an audio signal with pre-emphasis.

The input signal to the variable gain control unit 1 of FIG. 1 is a CD reproduction signal (strictly speaking C
D audio signal portion of the reproduced signal),
Therefore, in actuality, the circuit of FIG. 1 is entirely composed of digital circuits. The circuit of FIG. 1 can be configured by hardware or software by using a DSP (digital signal processor).

Next, the operation of the first embodiment will be described.
When the CD reproduction signal is input to the compressor shown in FIG. 1, the CD reproduction signal is sent to the variable gain control section 1 and the emphasis correction section 3, respectively. On the other hand, the emphasis detection section 5 is supplied with the control bits (4 bits) of the Q channel of the subcode in the CD reproduction signal, and reproduces the reproduction CD.
It is detected whether the signal is pre-emphasized.

The control bits (4 bits) of the Q channel of CD are defined as follows. “0000” 2-channel audio signal without pre-emphasis “1000” 4-channel audio signal without pre-emphasis “0001” 2-channel audio signal with pre-emphasis “1001” 4-channel audio signal with pre-emphasis

Now, assuming that the control bit of the Q channel is "0001", that is, a 2-channel audio signal with pre-emphasis, the emphasis detection section 5 outputs a detection signal with pre-emphasis to the emphasis correction section 3. ..

Upon receiving the detection signal with pre-emphasis from the emphasis detection section 5, the emphasis correction section 3 turns on the de-emphasis circuit having the frequency characteristic shown in FIG.
Then, the reproduced CD signal is de-emphasized. Due to this de-emphasis, C output from the emphasis correction unit 3
As shown in FIG. 3, the D signal is sent to the input signal level detector 4 as a CD reproduction signal having an original flat frequency characteristic without emphasis.

The input signal level detector 4 detects the signal level of the de-emphasized CD reproduction signal and sends the detection result to the variable gain controller 1 as a control signal.

The variable gain controller 1 responds to the signal level of the de-emphasized CD reproduction signal sent from the input signal level detector 4 with respect to the input CD reproduction signal as shown in FIG. After processing, output to the latter stage.

Therefore, even if the input signal is an audio signal with pre-emphasis, a normal compressor operation can be performed based on the signal level of the de-emphasized original audio signal. The effect will not change.

FIG. 4 shows a second embodiment of the present invention. In the second embodiment, the emphasis correction section 3 in FIG. 1 is arranged on the signal line 2, and the CD reproduction signal de-emphasized by the emphasis correction section 3 is supplied to the variable gain control section 1 and the input signal level detection section 4. It was designed to be sent.
In the case of this second embodiment, C transmitted on the signal line 2
Since the D reproduction signal is simultaneously de-emphasized by the emphasis correction unit 3, it is possible to eliminate the need for the de-emphasis of the reproduction signal, which is usually performed in the subsequent stage of the compressor before being output to the speaker.

FIG. 5 shows a third embodiment of the present invention. The third embodiment is provided with an equalizer-equipped input signal level detection unit 6, and the equalizer detects only the signal level of the low frequency part of the CD reproduction signal to detect the signal level of the low frequency part of the CD reproduction signal. CD on signal line 2 depending on
By controlling the gain of the reproduction signal, it can be used as a booster circuit for enhancing or attenuating the low frequency component of the musical sound reproduced from the speaker.

FIG. 6 shows a fourth embodiment of the present invention. In the fourth embodiment, the display circuit 7 such as a level meter or a spectrum analyzer is controlled by using the CD reproduction signal after being de-emphasized by the emphasis correction section 3.

In the above embodiments, the case of a CD is taken as an example, but the present invention can be applied to other audio devices such as DAT, cassette tape player, radio tuner and the like. In case of DAT, emphasis detection unit 5
The signal for detecting the presence or absence of emphasis given to
Main I of main data area of reproduced DAT signal
The subcode W ₁ in D may be used.

In the case of an analog type device such as a cassette tape player or a radio tuner, a signal for emphasis detection is not generally incorporated in the reproduced signal,
When converting a tape output signal or a tuner audio signal into a digital signal and handling it, the presence / absence of emphasis processing may be designated by the microcomputer and the processing may be performed.

Further, if the input / output characteristic of the variable gain control section 1 in the above-mentioned embodiment has the characteristic shown in FIG. 10 or 11, the above-mentioned embodiment can be used as it is as a limiter and an expander.

[0032]

As is clear from the above description,
According to the present invention, it is possible to perform a predetermined processing operation regardless of whether the input signal is emphasized or not, and always obtain a constant and constant processing effect.

[Brief description of drawings]

FIG. 1 is a block diagram of a first embodiment of the present invention.

FIG. 2 is a diagram showing an example of de-emphasis characteristics.

FIG. 3 is a diagram showing frequency characteristics after de-emphasis.

FIG. 4 is a block diagram of a second embodiment of the present invention.

FIG. 5 is a block diagram of a third embodiment of the present invention.

FIG. 6 is a block diagram of a fourth embodiment of the present invention.

FIG. 7 is a block diagram of a conventional example.

FIG. 8 is a diagram showing an example of input / output characteristics of a compressor.

FIG. 9 is a diagram showing an example of pre-emphasis characteristics.

FIG. 10 is a diagram showing an example of input / output characteristics of a limiter.

FIG. 11 is a diagram showing an example of input / output characteristics of the expander.

[Explanation of symbols]

 1 Variable Gain Control Section 2 Signal Line 3 Emphasis Correction Section 4 Input Signal Level Detection Section 5 Emphasis Detection Section 6 Input Signal Level Detection Section with Equalizer

Claims (1)

[Claims] 1. An input signal level detecting section comprising: a signal processing section for performing a predetermined signal processing on the input signal according to a signal level of the input signal; and an input signal level detecting section for detecting the signal level of the input signal. In the signal processing circuit configured to variably control the signal processing of the signal processing unit according to the signal level of the input signal detected in step 1, the emphasis detection unit that detects the presence or absence of pre-emphasis of the input signal, and the emphasis detection unit And an emphasis correction unit that deemphasizes an input signal based on an emphasis presence / absence signal that is output, and uses the output signal of the emphasis correction unit as an input signal of the input signal level detection unit. Signal processing circuit.