JPH07112320B2 - Sound field correction device - Google Patents

Description

The present invention relates to a transfer function of a sound field at a specific place such as a vehicle interior,
The present invention relates to a sound field correction device that corrects a desired transfer function.

2. Description of the Related Art FIG. 3 is a block diagram showing the configuration of a conventional sound field correction device. In FIG. 3, reference numeral 1 is an audio signal generator (digital) such as a CD player, which is connected to the sound field correction filter 2. Reference numeral 2 is a filter having a characteristic for correcting the transfer characteristic of the sound field measured in advance. Reference numeral 3 is a D / A converter for converting the output of the sound field correction filter into analog, 4 is an amplifier for amplifying the analog signal 3, and 5 is a speaker connected to the amplifier 4.

Next, the operation of the above conventional example will be described. In FIG. 3, the digital signal output from the acoustic signal generator 1 is input to the sound field correction filter 2, filtered, converted into an analog signal by the D / A converter 3, and amplified by the amplifier 4. And is emitted from the speaker 5.

Here, the transfer function of the sound field placed in the speaker 5 from the speaker input terminal to the listening position is H, and the desired transfer function from the input of the sound field correction filter to the listening position is K, and is sent to the sound field correction filter 2. Input signal of I, sound field correction filter 2
Where A is the transfer function of A and the transfer function of the D / A converter 3 and the amplifier 4 is 1, the following relationship holds (where H, K, I,
A, etc. are expressed in the frequency domain).

H · A · I = K · I ∴ A = K / H As described above, even in the above-described conventional sound field correction device, the sound field characteristic is set by setting the transfer function A of the sound field correction filter as the above equation. Can be corrected.

However, in the conventional sound field correction apparatus described above, when the transfer function H to be corrected has a sharp dip, the transfer function A of the sound field correction filter is used to try to correct the dip. Had a problem that the signal reproduced from the speaker had a peak in a specific number of weekdays and was unnatural to the sense of hearing.

The present invention solves such conventional problems,
It is an object of the present invention to provide an excellent sound field correction device capable of reproducing a corrected signal from a speaker so as not to be unnatural to the listener.

Means for Solving the Problems In order to achieve the above object, the present invention provides a conventional sound field correction device with a peak correction filter, preserves the characteristics of the transfer function A of the sound field correction filter, and only has a sharp peak. Is smoothed.

Effect According to the present invention, therefore, by correcting only the sharp peak of the frequency characteristic of the sound field correction filter, the peak can be smoothed, and only the sharp peak is smoothed. The frequency characteristic of the field correction filter can be preserved, and an audibly more natural signal can be reproduced from the speaker.

Practical Example FIG. 1 is a block diagram showing the configuration of an example of the present invention. In FIG. 1, reference numeral 1 is a digital acoustic signal generator such as a CD player, the output of which is connected to a sound field correction filter 2. The sound field correction filter 2 is a digital filter for correcting the transfer function of the sound field from the speaker 5 to the listening point, and FIR (Finite Impulse Response)
Composed of filters. The coefficient of the FIR filter is calculated and set by the filter coefficient calculating means 6 described later.

3 is D / for converting the sound field-corrected signal into an analog signal
In the A converter, 4 is an amplifier that amplifies the analog signal, and 5 is a speaker that converts the output of the amplifier 4 into sound.

6 is a filter coefficient calculation means, which has an input terminal
Impulse response h from the speaker input terminal to the listening point
(I) is input, and the desired impulse response k (i) of the entire system from the sound field correction filter to the listening point is input to the input terminal.

61 is an FFT (F
ast Fourier Transform), h (i) and k (i) are input, converted into H (n) and K (n), and output. A filter characteristic calculator 62 outputs the filter characteristic A (n) by the calculation of the following equation.

A (n) = K (n) / H (n) Reference numeral 63 is a peak correction filter, which is used for smoothing only the sharp peak of A (n) so that A at a certain frequency k.
With the value of (n) as A (k), the following calculation is performed.

A (k) = (bA (k) + cB) / d; (when A (k) ≧ aB) = A (k); (when A (k) <aB) Here, B is the average value of L pieces of A (i) before and after A (k), and a, b, c, d, j, L, etc. are properly selected according to the state of the sound field.

The above equation replaces A (k) with a smaller value if A (k) is greater than aB.

Reference numeral 64 is an inverse FFT that performs an inverse discrete Fourier transform of peak-corrected A (k), and its output is a correction coefficient expressed in the time domain. This correction coefficient is preset as a coefficient of the sound field correction filter 2.

Next, the operation of the above embodiment will be described.

First, the operation of setting the coefficient of the sound field correction filter 2 will be described.

When the impulse response h (i) of the listening point measured in advance is input to the input terminal of the filter coefficient calculation means 6 and the desired impulse response k (i) is input to the input terminal, these are discrete Fourier transformed by the FFT 61. , H (n) and K (n), respectively. Upon receiving this output, the filter characteristic calculator 62 calculates the filter characteristic A (n), the peak correction filter 63 performs peak correction, and the inverse FFT 64 performs inverse discrete Fourier transform to obtain the correction coefficient. This correction coefficient is set in the sound field correction filter 2, and the filter characteristic A (n) is determined.

Next, the operation of the sound field correction device will be described.

The digital signal I (n) output from the acoustic signal generator 1 is
D / A through the sound field correction filter 2 (transfer function A (n))
After being converted into an analog signal by the converter 3 and amplified by the amplifier 4, the speaker 5 reaches the listening point as a (transfer function H (n)) acoustic signal.

Therefore, the signal at the listening point is H (n) A (n) I (n) = H (n) K (n) / H (n)
I (n) = K (n) I (n), and the desired sound field K (n) I (n) can be obtained.

As described above, according to the above-described embodiment, the sharp peak of the frequency characteristic of the sound field correction filter is smoothed, and is not smoothed in other places, so that an audibly natural sound can be reproduced.

FIG. 2 is a block diagram of a filter coefficient calculating means which is a main part of another embodiment of the present invention. In this embodiment, the peak correction filter 63 does not perform the peak correction of the filter characteristic A (n), but the transfer characteristic H (n) of the sound field placed in the speaker.
The dip correction or the desired peak of the transfer function K (n) is corrected in the same manner as in the first embodiment. The filter characteristic A (n) is H in the filter characteristic calculation means 62.
It is calculated from (n) and K (n). Therefore, this embodiment also has the same effect as that of the first embodiment.

EFFECTS OF THE INVENTION As is apparent from the above-described embodiment, the present invention is provided with a peak correction filter so as to smooth only a sharp peak in the transfer characteristic of the sound field correction filter. It has an effect that a sound can be provided to a listener.

[Brief description of drawings]

FIG. 1 is a block diagram of a sound field correction apparatus according to an embodiment of the present invention, FIG. 2 is a block diagram of essential parts of the apparatus according to another embodiment of the present invention, and FIG. 3 is a conventional sound field correction apparatus. It is a block diagram. 1 ... Acoustic signal generator, 2 ... Sound field correction filter, 3 ...
… D / A converter, 4 …… Amplifier, 5 …… Speaker, 6 ……
Filter coefficient calculation means, 61 ... FFT, 62 ... filter characteristic calculator, 63 ... peak correction filter, 61 ... inverse FFT.

Claims (2)

[Claims] 1. A first FFT for Fourier transforming an impulse response signal from a speaker input terminal to a listening point and a second FFT for Fourier transforming a desired impulse response signal from a sound field correction filter to a listening point through a speaker. A calculating means for calculating the ratio of the outputs of the first and second FFTs, a peak correcting means for smoothing a sharp peak value in the output of the calculating means, and an inverse FFT for inverse Fourier transforming the output of the peak correcting means. Filter coefficient calculation means, a sound field correction filter that corrects and outputs an input signal from a digital sound source by a digital filter that sets the coefficient calculated by this calculation means, and the output of this sound field correction filter is D / A sound field correction device equipped with a means for converting and amplifying and outputting sound from a speaker. 2. A first FFT for Fourier transforming an impulse response signal from a speaker input terminal to a listening point and a second FFT for Fourier transforming a desired impulse response signal from a sound field correction filter to a listening point through a speaker. An output of the first and second peak correction means for performing the peak correction of the outputs of the first and second FFTs and a calculation means for calculating the ratio of the outputs of the first and second peak correction means. A filter coefficient calculation means having an inverse FFT for performing an inverse Fourier transform, a sound field correction filter for correcting and outputting an input signal from a digital sound source by a digital filter in which the coefficient calculated by this calculation means is set, A sound field correction device having means for D / A converting the output of a sound field correction filter, amplifying it, and outputting sound from a speaker.