JPH0252445B2 - - Google Patents

Description

TECHNICAL FIELD The present invention relates to a vehicle-mounted frequency characteristic detection device, and more particularly to a vehicle-mounted frequency characteristic detection device that also has an automatic volume adjustment function.

BACKGROUND ART In a frequency characteristic detection device such as a vehicle-mounted spectrum analyzer, the sound field frequency distribution at an appropriate location in the vehicle interior, for example, near the passenger's ear canal is used as a frequency spectrum to display two signals on a photodiode display, etc.
It is displayed using a dimensional display means.

An in-vehicle spectrum analyzer detects changes in the sound field as an electrical signal using, for example, a microphone inserted into the passenger's ear canal, divides the electrical signal into multiple different frequency band components using a bandpass filter, and then calculates each frequency. The instantaneous values of the components are displayed two-dimensionally using a light emitting diode display or the like. In this case, when driving a two-dimensional display, the frequency component is digitized and used as a driving input for the two-dimensional display.

On the other hand, an automatic volume adjustment device is also known that automatically changes the amplification factor of an amplifier that amplifies an audio signal of an in-vehicle audio device in accordance with a noise level such as engine sound.

Although it is preferable to increase the resolution of noise level detection by such an automatic volume adjustment device because it allows finer control, there is a problem in that it increases the cost.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a device that performs highly accurate automatic volume adjustment by utilizing an on-vehicle spectrum analyzer.

In the in-vehicle frequency characteristic detection device according to the present invention, the sound level at a predetermined location in the vehicle interior is detected for each of a plurality of frequency bands and generated as a frequency range signal, while the noise level in the vehicle interior is detected to obtain a noise level signal and the sound level is detected for each frequency band. The frequency range signal and the noise level signal are selectively logarithmically compressed and then digitized, and the secondary element representation and the amplification degree of the audio amplifier are adjusted based on the digital signal obtained.

Embodiment Hereinafter, an in-vehicle frequency characteristic detection device with an automatic volume adjustment function, which is an embodiment of the present invention, will be described in detail with reference to the drawings.

In the figure, a microphone 1 is placed at a suitable location in the interior of a passenger car and sends out a noise signal representing the noise inside the vehicle. The noise signal is amplified by a variable amplification amplifier 2 and then passed through a low pass filter 3.
, only the low frequency components are supplied to the rectifier circuit 4. The output of the rectifier circuit 4 is further smoothed by a smoothing circuit 5 and sent to the input terminal ch0 of the switching relay switch 6.
supplied to The switching relay switch 6 relays any one of the input signals supplied to its input terminals ch0 to ch7 to the logarithmic compression circuit 7 in accordance with the channel designation code signal supplied via the designated input line group. The A/D converter 8 converts the level of the logarithmically compressed signal into, for example, a 4-bit binary code signal and outputs it to the signal line group B. The binary code signals on the signal line group B are supplied to a control circuit 9 and a decoder 10 comprising a microprocessor or the like. The decoder 10 converts the binary code signal into a decimal code signal and supplies it to the vertical axis input terminal of a two-dimensional display 11 consisting of a light emitting diode matrix.

On the other hand, the control circuit 9 adjusts the amplification degree of the amplifier 2 via the line C according to the content of the signal corresponding to the terminal ch0 among the binary code signals supplied from the signal line group B. Further, the control circuit 9
The switching relay switch 6 sends to the line group A a channel designation code signal designating the channel to be relayed. The channel designation code signal of the line group A is also supplied to the decoder 12, and the decoder 12 converts the channel designation code signal into a decimal code signal and sends it to the horizontal axis drive terminal of the display 11 via the signal line group D. supply External commands to the control circuit 9 are issued via the keyboard 13.

On the other hand, the microphone 14 is attached, for example, to the passenger's ear canal and connected via a cord to one fixed contact _S1 of the changeover switch SW via a jack terminal provided at a suitable location in the vehicle interior. The other fixed contact of the changeover switch SW is connected to an audio signal input terminal 15 from an in-vehicle audio device (not shown) such as a car stereo. A movable contact of the changeover switch SW is connected to an input terminal of the amplifier 16.
The output signal of the amplifier 16 is passed through a bandpass filter.
The signals are divided into frequency bands by BPF1 to BPF7 and supplied as frequency range signals to input terminals ch1 to ch7 of switching relay switch 6 via series circuits of rectifiers _D1 to _D7 and smoothing circuits SM1 to SM7.

The audio signal that has passed through the audio input terminal 15 is amplified by a variable amplification amplifier 16 composed of an operational amplifier OP and a feedback resistor R _f , and is then sent to an audio output terminal such as a speaker (not shown). ).

The operation of the apparatus having the above configuration will be explained below.

When the power is turned on, the control circuit 9 sequentially sends out channel designation code signals (3 bits in this example) onto the signal line A at a predetermined frequency determined by the internal clock. The changeover relay switch 6 is
Since the noise level signal and the frequency range signal supplied to the input terminals ch0 to ch7 specified by the channel designation code signal are sequentially and selectively relayed,
A high level signal represented by nine levels of values is supplied from the decoder 10 to the vertical axis input terminal of the display 11. Here, since the decoder 12 sequentially supplies a low level signal to any line of the signal line group D in response to the channel designation of ch1 to ch7, the display 11 displays a signal in the horizontal axis direction corresponding to each channel. Level changes for each frequency range are displayed in order.

On the other hand, the gain G of the amplifier 16 is adjusted by changing the feedback resistance value R _f by the control circuit 9 so as to satisfy the following equation. In other words, ΔG = (N - α) β Here, ΔG is the gain adjustment amount N is the noise level (dBA), α is the reference noise level (dBA), and β is the amount of gain increase per unit level increase in noise (unitless). ), and both α and β can be set via the keyboard 13 depending on the vehicle type, etc. for example,
When α=40 dBA and β=0.4, when N=60 dBA, the gain adjustment amount ΔG=0.4×(60−40)=16, and the control circuit 9 adjusts the resistor R _f so as to increase the gain by 16 dBA.

Here, if the noise level obtained by the microphone 1 is n and the gain of the amplifier 2 is k, the output of the logarithmic circuit 7 is 20log(k・n)=20logk+
20logn=N-α. Here, N=20logn, α
= −20logk. Therefore, the control circuit 9 adjusts the gain of the amplifier 2 so that α=-20logk holds.

The operation of the control circuit 9 described above is expressed in a flowchart as shown in FIG.

In the embodiments described above, the display 11 may be replaced with a printer or other output device.

Effects of the Invention As is clear from the above, the frequency characteristic device according to the present invention detects the output of the in-vehicle audio or the frequency distribution characteristics of the sound field inside the vehicle, and at the same time automatically adjusts the audio output level according to the noise level. Because of the logarithmic compression processing, it is possible to adjust the pitch to be evenly spaced according to the auditory sense due to the logarithmic compression processing.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is an operation flowchart of the control circuit in FIG. 1. Explanation of symbols of main parts 1, 14... Microphone, 6... Relay switch, 11... Two-dimensional display, OP... Operational amplifier.

Claims (1)

[Claims] 1. Frequency analysis means for dividing sound at a predetermined position in the vehicle interior into a plurality of frequency range signals; noise level signal generation means representing the noise level in the vehicle interior;
a selection switch for sequentially switching and relaying any one of the frequency range signal and the noise level signal; a logarithmic compression means for logarithmically compressing the output signal of the selection switch means; and a level of the output signal of the logarithm compression means. An A/D conversion means for generating a digital signal, a display means for two-dimensionally displaying a change in the digital signal in synchronization with a switching operation of the selection switch means, and a selection switch means for relaying the noise level signal. 1. An on-vehicle frequency characteristic detection device comprising: amplifying means for amplifying an input audio signal with an amplification degree corresponding to the digital signal when the digital signal is being input.