NOVEL METHOD FOR IMPROVING THE DIFFUSION OF MUSICAL LOW FREQUENCIES ACCORDING TO THE AUDIO LEVEL

Abstract

According to this method, the playback level of the music is measured as compared to a reference level and if the playback level is lower than the reference level the level of the low frequencies is increased in a manner substantially proportional to the difference between the reference level and the measured level to maintain the tonal balance of the musical piece.

Claims

1. A method of compensating the low frequencies level of a musical reproduction system increasing the relative level of low frequencies when the reproduction level decreases controlled by a microphone measuring the sound pressure in the listener's environment and characterized in that the sound pressure is measured through a weighting filter decreasing the influence of the low frequencies and by the fact that the increase of the low frequencies is canceled in the absence of sound modulation.

2. Low frequencies processing device implementing the method according to claim 1 comprising a calibrated microphone, a weighting filter A, a rectifier circuit, a voltage configurator adapted to control a voltage controlled amplifier allowing to increase the level of low frequencies according to the sound level detected by the microphone and means for detecting the level of the source signal commanding the cancellation of the increase of the relative level of the low frequencies in the absence of sound modulation.

3. Sound reproduction equipment equipped with a low frequencies processing device according to the method of claim 2.

Description

[0018] FIG. 1 is a general diagram of a device according to the method of the present invention. A sound modulation source 1 supplies a 1:2 low-pass filter. This filter supplies a voltage-controlled amplifier 3 which itself feeds a power amplifier 4 which sums the signal coming from 3 and the signal from 1 and supplies the speaker 5. The speaker thus emits a modulation which is the sum between the original modulation and the same original modulation filtered by a first-order low-pass filter whose level varies according to the sound pressure level emitted by the loudspeaker.

[0019] For this a microphone 6 delivers a voltage proportional to the sound pressure in the environment of the listener. This signal is filtered by a weighting filter 7.

[0020] Very good results are obtained by filtering the signal from the microphone using a filter reproducing the weighting curve A defined by the IEC 61672 standard.

[0021] The voltage from 7 is rectified by the rectifier without threshold 8. The DC voltage from 8 supplies the voltage configurator 9 responsible for developing a voltage able to drive the amplifier 3.

[0022] The modulation from 1 is introduced into the circuit 10 arranged to command at the circuit 9 the cancellation of increase the level of bass frequencies in the absence of signal at the output of the source 1.

[0023] The transfer function of a low-pass filter composed of a resistor R and a capacitor C equal to:

[00001]$\frac{1}{1+\mathrm{jwRC}}$

[0024] G being the gain of the amplifier 3, the assembly of FIG. 1 provides a sound pressure proportional to:

[00002]$\left[1+\frac{G}{1+\mathrm{jwRC}}\right]$

[0025] Whose module is equal to:

[00003]$\sqrt{\frac{{\left(G+1\right)}^2+{\left(\mathrm{RCw}\right)}^2}{1+{\left(\mathrm{RCw}\right)}^2}}$

[0026] The curves of FIG. 2 are the decibel value of this module between 60 dB and 100 dB at different frequencies by taking RC=0.026.

[0027] Curve 1 is the response curve of the device of FIG. 1 for an acoustic level of 60 dB. It is obtained with G=20 that is to say 26 dB.

[0028] Curve 2 is the response curve of the device of FIG. 1 for an acoustic level of 70 dB. It is obtained with G=10 that is to say 20 dB.

[0029] Curve 3 is the response curve of the device of FIG. 1 for an acoustic level of 80 dB. It is obtained with G=5 that is to say 14 dB.

[0030] Curve 4 is the response curve of the device of FIG. 1 for an acoustic level of 90 dB. It is obtained with G=2.5 that is to say 8 dB.

[0031] Curve 5 is the response curve of the device of FIG. 1 for an acoustic level of 100 dB. It is obtained with G=1.25 that is to say 2 dB.

[0032] The amplifier 3 is a circuit THAT 2181 whose gain is equal to 1 when its control voltage is zero and which increases by 1 dB when its control voltage decreases by 0.006 volts.

[0033] At 60 dB the control voltage should be 0.156 volts

[0034] At 70 dB the control voltage should be 0.120 volts

[0035] At 80 dB the control voltage must be 0.084 volts

[0036] At 90 dB the control voltage must be 0.048 volts

[0037] At 100 dB the control voltage must be 0.012 volts

[0038] The voltage from the circuit 8 is equal to: [0039] 10 volts to 100 dB [0040] 3.3 volts at 90 dB [0041] 1 volt at 80 dB [0042] 0.33 volts to 70 dB [0043] 0.1 volts to 60 dB

[0044] It can be deduced that the output voltage of the circuit 9 must be equal to:

[00004]$\log .Math..Math.\frac{V_8}{15}-0,084.Math..Math.\mathrm{volts}$

[0045] This device could equip sound reproduction equipment.