JPH07235850A - Audio equipment - Google Patents

Abstract

PURPOSE:To adjust an audio output so as to obtain a best listening sound volume characteristic at all times even when an external noise is fluctuated in the audio equipment. CONSTITUTION:After an audio signal outputted from an audio source 10 is converted into a digital signal by an A/D converter circuit 11, the digital signal is processed by a digital signal processing circuit 12 and the processed signal is sounded from a speaker 15 via a D/A converter circuit 13 and a power amplifier 14. In this case, a controller 17 controls an output level of the digital signal processing circuit 12 based on a value detected by an external noise level detector 16. A dynamic range of an outputted audio signal is controlled by controlling the output level and a level of a signal with a small level is increased when a level of an external noise is at least high.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio device which has a large change in external noise level (noise) and is suitable for use in, for example, a vehicle.

[0002]

2. Description of the Related Art In a vehicle mounted compact disc (CD) player or the like, or an audio device used outdoors, the listening environment greatly changes depending on the ambient noise state, and it is difficult to always output a good sound. For example, when playing music on a CD in a running car, in the case of a quiet song, noise caused by running the car (hereinafter, not caused by an audio device) even at a normal playback volume level. External noise etc. are called "external noise".

Therefore, as proposed by the applicant of the present invention, there has been proposed an audio device capable of obtaining a voice output signal having a compressed dynamic range when the external noise level is high, and an example thereof is proposed. It is shown in FIG.
In the figure, 1 is a CD reproducing device, 2 is a power amplifier, and 3 is a speaker. In this audio device, a normal CD playback sound can be obtained in the a mode in which the switch S is connected to the a terminal, but the switch S is set to b by the operation of the user.
When connected to the terminal and set to the b mode, the reproduction signal output as an analog signal from the CD reproducing device 1 is supplied to the dynamic range compression circuit 4, and is shown by a solid line in FIG. 7 by means of output gain adjustment or the like. As described above, an output signal having a compressed dynamic range with respect to the input signal is obtained. In other words, the output sound is not masked even when the external noise level is high by increasing the amplification degree of the signal component in the low output level region where it is difficult to obtain a good reproduction state because it is masked by external noise. is there.

[0004]

However, in this audio apparatus, since the external noise level is not always constant, the following problems occur.
In the audio device shown in FIG. 6, the sound reproduced and output by the signal compressed in the dynamic range, that is, the sound in the b mode is somewhat unnatural sound compared with the CD reproduced sound in the normal a mode. It is inevitable that it will become. Therefore, when the external noise level is high, the audio sound itself is considerably uncomfortable to be heard as a reproduced sound even if the reproduced sound state is not so much noticed due to the bad listening environment when the external noise level is lowered. Therefore, if the user wants to hear the reproduced sound always in the best condition, the user has to select the a mode or the b mode according to the noise level,
The switching operation of the switch S must be frequently performed.

In particular, in the case of a vehicle-mounted audio device, the external noise level frequently and considerably fluctuates depending on the running speed of the vehicle, so that the switch S
However, there is a drawback that the switching operation of is rather troublesome, and in the end, it was not suitable for practical use.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and based on control data supplied from a plurality of control data stored in a memory means, input data is input. The digital signal processing means for compressing and outputting the dynamic range of the generated signal is provided, and further, as means for supplying control data, an external noise level detecting means and an external noise level detected by the external noise level detecting means are provided. Thus, the audio device is provided with the selection control means capable of selecting and reading out predetermined control data from the memory means and supplying the selected control data to the digital signal processing means.

[0007]

In the above structure, the selection control means reads the signal processing control data from the memory means according to the external noise level detected by the external noise level detecting means and supplies the signal processing control data to the digital signal processing means. In the means, the dynamic range of the input signal is compressed based on this control data, so that the output voice can always obtain the optimum state even if the level of the external noise changes.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows one embodiment of the present invention. In the figure, 10 is an audio source and 10A is C
D playback device, 10B a tape playback device, and 10C a radio tuner. Reference numeral 11 denotes an A / D conversion circuit, and the analog signal output from the tape reproducing device 10B and the radio tuner 10C is converted into a digital signal by the A / D conversion circuit 11 and input to the digital signal processing circuit 12. When the output signal of the CD reproducing device 10A is already D / A converted into an analog signal in the CD reproducing device 10A, the output signal of the CD reproducing device 10A is also A.
It is input to the digital signal processing circuit 12 via the / D conversion circuit 11. The digital signal processing circuit 12 is
Under control of a microcomputer 17, which will be described later, the input digital signal can be subjected to various kinds of processing and output. The output signal is converted into an analog signal by the D / A conversion circuit 13, and the speaker 1 via the power amplifier 14.
5 is output as a voice. 16 is a noise level detection device that constantly detects the level of external noise, 17 is a microcomputer, 17A is a controller,
Reference numeral 17B is a memory in which control data of the digital signal processing circuit 12 is stored.

If the noise level detecting device 16 is, for example, an on-vehicle audio device, an external noise level is estimated by using an acceleration pickup or by detecting the engine speed, and the estimated value is calculated. It may be detected as a noise level.When directly measuring the noise level, the output voice level is also known at the same time, and the output voice level is subtracted from the detected ambient voice level. Should be detected as a noise level.

As described above, the audio signal is provided with the digital signal processing circuit 12, and the digital signal processing circuit 12 is configured to be controlled by the microcomputer 17 according to the noise level. On the other hand, the compression state of the dynamic range of the output signal can be automatically changed so that the audio output can always be obtained in the best listening state. In other words, it is better to not compress the dynamic range if there is almost no external noise or if it is in a state where it is not disturbing, because the voice with compressed dynamic range is naturally more difficult to hear than the voice without normal compression, In the case of a large value, the listening condition can be improved by raising the volume of a small sound that is easily masked by external noise by raising the low output level region. Therefore, in order to always obtain the best listening state, it is sufficient to gradually change the compression state of the dynamic range of the audio output signal while the external noise level changes from the state near zero to the maximum noise level state. The operation will be described below.

In this embodiment, the digital signal processing circuit 12 is used.
In the above, the output digital signal obtained by performing the dynamic range compression processing on the input digital signal is obtained. This dynamic range compression processing is read from the memory 17B by the controller 17A according to the noise level fluctuation. This is performed based on the control data to be output and supplied to the digital signal processing circuit 12, that is, the conversion coefficient of the output signal level with respect to the input signal level. Therefore, the controller 1
As shown in the flow chart of FIG. 2, the operation of 7A is such that the noise level (NL _tx ) at that time is changed to N by the signal supplied from the noise level detection device 16.
It is detected which class among the noise level stages set as L ₀ , NL ₁ , NL ₂ ... NL _m (stages preliminarily divided into a predetermined number of stages according to the strength of noise) ( 101).

Since the external noise level is usually constantly changing finely, the signal detected by the noise level detecting device 16 is appropriately filtered to be an average noise level for a certain time point. It is preferable that the detection signal be directly supplied to the controller 17A, but the detection signal is directly input to the controller 17A.
The averaging process may be performed before determining the noise level stage within 7A.

The current noise level (NL _tx ) is NL
_When the level of _{0 to} NL _m is determined, it is next determined whether or not the noise level level is different from the noise level level of the previous noise level (NL _{t (x-1)} ). The determination is made (102), and if they are different, the control data corresponding to the new noise level stage is read from the memory 17B (103). Then, the read control data is supplied to the digital signal processing circuit 12 (104), and in the digital signal processing circuit 12, as described above, based on the conversion coefficient specified in the control data, the CD reproducing device 10A. The input signal from the device is processed, and the signal whose dynamic range is in a predetermined compressed state is output.

In the flow chart of FIG. 2,
The operation of the digital signal processing circuit can be similarly controlled by the operation of the controller 17A in which step 102 is omitted.

By the way, the control data stored in the memory 17B is, for example, as shown in FIG. 3, one set of coefficient groups for each noise level stage NL _{0 to} NL _m , and each noise level stage is set. Digital signal processing circuit 12 for each
Each conversion coefficient is set for each level Di _{1 to} Di _n of the input signal Di to the input. Therefore, for example, when the input signal Di is an 8-bit code, it is preferable that 256 coefficients are prepared as a set of control data.

By storing the control data in such a form, for example, N having a relatively low noise level can be obtained.
In the L ₁ class, n coefficients (K _{1, 1} , K _{1, 2} , K _{1, 3} ... K _{1, n} ) are read out as control data. Then, the input signal Di is processed in the digital signal processing circuit 12 based on the respective coefficient values, so that the desired output signal Do can be obtained as the digital signal processing circuit 12. That is, the output signal Do to the input signal components Di _x of the input signal Di, the input signal Di coefficient set corresponding to the level of _x K _{1 · x}
Will be output as a multiplied output signal Do _x .

Therefore, for example, if the noise level is NL
_When the relationship between the input and output signal levels is set as shown by the solid line in FIG. 4 at the time of ₃ , the coefficients K _{3 1} , K ₃ .2 ... K ₃ Depending on _n , input signal levels Di _{1 to} Di _n having a normal dynamic range
(DB) is converted to an output signal level Do ₁ to DO _n (dB) in the relationship shown by the solid line in the digital signal processing circuit 12, so that the dynamic range is output as a signal compressed in DR _3. The control data based on this coefficient group is read by the operation of the controller 17A described above according to the change in the noise level stage and supplied to the digital signal processing circuit 12. Therefore, for example, the noise level changes from NL ₃ to NL _8. If it suddenly rises to
Coefficients K _{8 ・ 1} , K _{8 ・ 2} ... K as control data for NL _{8
8 · n} is newly read out and supplied to the digital signal processing circuit 12. Therefore, the input signal levels Di _{1 to} Di _n (dB) are, for example, in the relationship shown by the dotted line in the figure,
Is converted to an output signal level _{Do 1 '~Do n' (dB} ), it becomes dynamic range output signal is further compressed to DR ₈ from DR ₃ is obtained.

Therefore, by appropriately setting and storing the coefficient value in each control data group, the output signal is controlled as an audio signal having a dynamic range capable of always obtaining the best listening condition. It will be possible. Further, since the compression state of the dynamic range according to the noise level is determined by the coefficient in the control data, for example, FIG.
As shown in (c), in each state from the case where the noise level is NL _{0 to} the case NL _m , various settings can be made as the states from DR ₀ to DR _m as the dynamic range of the output signal. The optimum coefficient value may be stored in consideration of the usage pattern, characteristics, etc. of the audio device.

Alternatively, the memory 17B may be configured as a rewritable memory so that the coefficient value can be changed so that the user can set the dynamic range according to the noise level according to his or her preference. There is almost no external noise (NL
_{In the case of 0} ), it is not necessary to compress the dynamic range, so that as the control data at NL ₀ , as shown in FIG. 3, all the values of the coefficients K ₀ ... K ₀ .n are set to 1 Alternatively, the control data may not be stored, and the controller 17A may control the digital signal processing circuit 12 not to perform the signal processing when NL ₀ .

[0020]

As described above, according to the audio device of the present invention, particularly in an audio device to which a music piece having a wide dynamic range is input, the audio device is emitted from a speaker or the like corresponding to the external noise level in the listening environment. Since the dynamic range of the sound pressure is set, for example, in an environment in which external noise is large, at least the signal level in the low frequency band is raised regardless of the frequency characteristic to compress the entire dynamic range. for that reason,
A low level sound that is easily buried in noise becomes easy to hear, and at the same time, a high level sound can be clearly heard without being distorted due to saturation of an amplifier.

That is, the music can be heard without distortion as compared with the one in which the volume level is simply increased at the time of noise, and the music can be heard in a state where the driver does not feel uncomfortable even while traveling on a congested road by a car or the like. Can be enjoyed, which is a practical effect particularly when the audio device is mounted on a vehicle.

[Brief description of drawings]

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

FIG. 2 is a flowchart showing the operation of the microcomputer of the present invention.

FIG. 3 is an explanatory diagram of a form of data stored in a memory of the present invention.

FIG. 4 is an explanatory diagram of a dynamic range compression operation.

5A, 5B and 5C are explanatory diagrams of a dynamic range compression mode.

FIG. 6 is a block diagram showing a prior art of the present invention.

FIG. 7 is an explanatory diagram of a conventional dynamic range compression operation.

[Explanation of symbols]

10 audio source 11 A / D conversion circuit 12 digital signal processing circuit 13 D / A conversion circuit 16 noise level detection device 17 microcomputer 17A controller 17B memory DR _{0 to} DR _m dynamic range

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H04R 3/00 310 // G11B 20/00 Z 9294-5D

Claims (1)

[Claims] 1. A digital signal processing means capable of forming a desired output signal by converting input signals output from various audio sources into digital signals and performing signal processing based on specific control data. A noise level detecting means capable of detecting an external noise level; a memory means for storing a plurality of control data for controlling a signal processing operation of the digital signal processing means; and an external means detected by the noise level detecting means. Selection control means capable of selectively reading a group of control data from the memory means according to a noise level and supplying the control data to the digital signal processing means, wherein the one group of control data is the external noise level. Becomes high, at least the low level of the input signal is raised and the dynamics of the output signal are increased. Audio apparatus characterized by range is formed so as to be compressed.