FR2469039A1 - Variable frequency response audio amplifier - has series of switchable filters to provide constant output for audiometry - Google Patents

Abstract

The amplifier consists of a set of low pass filters of either increasing or diminishing cut offs and a set of delays interconnected by switches so as to allow the signals passed by each filter to be either passed or blocked to the output. The output level is regulated to remain constant. The extent of each delay is controlled separately by an oscillator and a processor connected to a controller which controls the switching of the parts of each filter. The filter outputs are mixed together before the output is regulated. Two of the amplifiers are used in parallel, one to each ear, and each filter may be switched progressively in and out of circuit. A mixer simultaneously receives all of the output signals from the series of filters and is directly connected to an intensity controller.

Description

The subject of the present invention is an automatic device making it possible to amplify the sound frequencies of a signal in a differential manner as well as the application of this device to the production of a listening educational device.

We know that it is possible to treat certain listening and speech impairments of a patient by making him hear suitably distorted sounds by filtering at certain particular frequencies. Sounds thus filtered are also used for the implementation of so-called listening education or audio-psycho-phonological techniques. The sounds that are heard by the patient wearing a headset can consist of classical music or the pre-recorded voice of another person such as that of the patient's mother. The magnetic tapes comprising such a succession in time of suitably filtered recordings are usually produced essentially manually by sequential switching of a plurality of high-pass filters at different cut-off frequencies.

According to the treatments envisaged, two main types of differential filtering of sound frequencies are thus produced.

In a first category, the sounds are all filters at the same high cutoff frequency; in a second category, the filtering carried out is decreasing or progressive depending on the frequency. We can thus find on such a previously recorded magnetic tape, a succession of short periods of the order of a few minutes for each of which the filtering frequency is different and lower and higher or higher depending on the treatment. longed for.

 It is also necessary during this manual work of differential amplification, to carry out a readjustment of the sound intensity at each change of filtering frequency. Indeed, the higher the cutoff frequency during filtering, the more the signal loses its sound power.

 Ultimately, the magnetic tape comprising a succession of short periods filtered at different increasing or decreasing frequencies and the sound power of which has been kept substantially constant is then introduced into a listening device of known type. This device generally comprises two hearing channels connected to a pair of headphones and connected in parallel. Each of these hearing channels comprises a cut-off filter at a particular sound frequency, one of the channels comprising a low-pass filter and the other channel a high-pass filter.

The apparatus further comprises switching means progressively switching on and off alternately each of the filters at each rising and falling edge of an input sound signal. In this way, the signals corresponding to the low frequencies, that is to say the low tones, are first of all transmitted only, then they are followed by the high frequency signals corresponding to the higher tones. This distortion is performed for each input signal at the time of the rising edge. For more details, reference may be made to French patent 1,195,239 which describes such a device in detail.

 The subject of the present invention is the production of a device making it possible to carry out automatically the various operations which were hitherto carried out manually. The invention makes it possible in particular to automate the switching of filters of different frequencies and to automatically level the sound power of the signal as a function of the filtering frequency of each filter.

The automatic device for differential amplification of sound frequencies according to the invention thus comprises a series of cut-off filters at different increasing or decreasing frequencies. According to the invention, the automatic device comprises successive time delay means connected to a plurality of switching means. Each of the switching means is associated with a cut-off filter so as to block or authorize the emission of a filtered output signal. The device also comprises sound intensity regulation means receiving the output signals from the aforementioned filters and keeping the sound intensity constant.

In a preferred embodiment of the invention, the successive time delay means comprise an oscillator determining the duration of each time delay. In addition, the device comprises a counter connected to a decoder controlling a plurality of doors connected respectively in the circuit of each filter.

To allow the realization of sounds filtered successively according to increasingly high cut-off frequencies or according to increasingly low cut-off frequencies, the device can advantageously include an up-down counter connected to the aforementioned decoder.

The subject of the invention is also the production of a listening educator which incorporates an automatic device for differential amplification of sound frequencies according to the invention. In this way, the original sounds can be introduced directly into such an improved listening educational device to be automatically filtered by the device of the invention and directly supplied to the conventional listening educational device comprising the headphones. intended for the patient.

The invention will be better understood from the study of an embodiment described by way of nonlimiting example and illustrated by the appended drawings, in which
fig. l is a functional diagram of the various main elements of an automatic device according to the invention; and
fig. 2 is a block diagram of the main elements of an improved listening teaching apparatus including an automatic device according to the present invention.

As shown in FIG. 1, the automatic device for differential amplification of sound frequencies according to the invention comprises a pilot oscillator l provided with an adjustment member comprising for example a potentiometer 2 making it possible to vary the duration d an oscillation of the output signal 3. The duration of the oscillation may vary for example from a minimum value of approximately 10 minutes to a maximum value of approximately 90 minutes passing through a normal value of approximately 30 minutes.

The output signal 3 is supplied to an up-down counter 4 which can be placed in the counting position by action on the connection 5 or in the down-counting position by action on the connection 6. In counting mode, the output signal 7 re presents an increasing number for example from O to n. In countdown mode, the output signal 7 instead represents a decreasing number from n to O. A display device 8 receives the output signal 7 from the up-down counter 4 in order to allow the user to know during of the device's operation, what is the cut-off frequency used at a given time.

The output signal 7 from the up-down counter 4 is also supplied to the input of a decoder 9 controlled by a signal 10 coming from a switch also connected by the connection 11 to the up-down counter 4. The decoder 9 comprises a plurality of outputs lla, llb ... up to for example lîn each connected to the control input of a logic gate 12a, 12b ... 12n.

Each of the doors 12 is mounted at the output of a filter referenced respectively 13a, 13b ... 13n whose cutoff frequency is increasing for example from 125 Hz with a slope of 40 dB, 250 Hz / 40 dB ... 6000 Hz / 40 dB, 8000 Hz / 40 dB, up to for example 8000 Hz / 80 dB.

 The different circuits 14a, 14b ... up to 14n each comprising a filter 13 and a control door 12 are connected in parallel, supplied by means of an input adapter device 15 and provide a filtered signal as an output. on connection 16 which is connected to a three-position reversing switch 17. In the position shown in fig. 1, the switch 17 connects the connection 16 representing the output of all the circuits 14a ... 14n to a sound intensity regulating amplifier referenced 18 which supplies an output signal to an output adapter 19.

 The device further comprises a mixer 20 with n channels directly receiving the output signals from each of the filters 13a ... 13n upstream of the various doors 12a ... 12n. The output of the mixer 20 can be connected directly to the input of the regulating amplifier 18 when the switch 17 is in the position 21. The switch 17 also allows manual filtering when it is placed in the position 22.

The device of the invention operates in the following manner. When the switch 10 is placed in the operating position, the resulting pulse resets the up-down counter 4 to zero and unlocks the decoder 9. The counter 4 first displays zero on its output signal. Consequently, the first output 11a of the decoder 9 goes to the low state, unlocking the logic gate 12a and the corresponding filter 13a. The sound coming from the input adapter 15 and constituted for example by classical music or a prerecorded voice is then filtered at the lowest frequency of 125 Hz. The switch 17 being placed in automatic mode as shown in fig . 1, the sound thus filtered after being amplified by the intensity regulating amplifier 18 is delivered to the output of the device by the adapter 19.

At the end of a duration equal to the oscillation duration of the pilot oscillator 1 defined by the potentiometer 2 divided by the number of filters n, the counter 4 displays the digit 1 at the output. The decoder 9 then selects its second output 11b thus unlocking the second door 12b while again blocking the first door 12a. The sound transmitted by the input adapter 15 is then filtered by the second filter 13b at a higher frequency of 250 Hz. This succession of operations continues until the probe has been filtered by the last frequency filter 13n 8000 Hz with a slope of 80 dB.

In the up-down counter 4 counting mode, the differential amplification of the sound frequencies is done with increasingly high cut-off frequencies over time, thus making it possible to carry out a so-called "sonic feedback" processing in audio techniques. psycho-phonological. In the down-counting position, the up-down counter 4 makes it possible, on the contrary, to provide a differential amplification of the sound frequencies according to increasingly lower cut-off frequencies allowing the realization of a so-called "sonic delivery" treatment.

When the switch 17 is placed in its position 21, the automatic device of the invention allows the production of a sound constituted by the mixture of the n filterings obtained from the plurality of filters 13a, 13b ... 13n. We can thus obtain music enriched with high sounds for certain other applications. Finally, in position 22, the switch 17 allows, if desired for other applications, to produce a manually filtered soundtrack, the choice of the cutoff frequency then being made by a frequency switch not shown. in the figure placed outside the device and controlling the various filters 13a ... 13n.

On the functional diagram of fig. 2, we find, under the general reference 23, the entire automatic device for differential amplification of sound frequencies illustrated in FIG. 1. The device 23 can receive, depending on the position of the switches 24 and 25, a sound signal coming from a microphone connected to the connection 26 via a preamplifier 27 or coming from a tape recorder or other recording device connected at connection 28.

 The output of the automatic device 23 feeds via an amplifier 29 playing the role of adapter and mixer the two channels 30 and 31 connected in parallel with a listening device of conventional type. The high channel 30 includes a high pass filter 30a and a logic gate 30b. The low channel 31 comprises a low pass filter 31a and a control gate 31b. The two doors 30b and 31b are controlled by a switching and delay device 32 which also receives by the connection 33 the signal from the amplifier 29. The switching device 32 can be constituted in a manner known per se a threshold circuit and a bistable or monostable rocker capable of causing the opening or closing of the doors 30b and 31b. The signals from channels 30 and 31 feed the output amplifier 34 connected via a balancing device 35 to the two headphones of a headset 36. The system is completed by a measuring device 37 connected to the output of amplifier 29 and allowing the user to know the level of sound signals at the output of this amplifier.

Claims (5)

 1. Automatic device for differential amplification of sound frequencies comprising a series of cut-off filters at increasing or decreasing frequencies, characterized in that it comprises successive time delay means connected to a plurality of switching means, each of said means switching being associated with a cutoff filter so as to block or authorize the emission of a filtered output signal and sound intensity control means receiving the output signals of the aforementioned filters and keeping the sound intensity constant. 2. Automatic device according to claim 1, characterized in that the successive delay means comprise an oscillator determining the duration of each delay, a counter device connected to a decoder controlling a plurality of gates connected respectively in the circuit of each filter.  3. Automatic device according to claim 2, characterized in that it comprises an up-down counter connected to the decoder. 4. Automatic device according to any one of the preceding claims, characterized in that it further comprises a mixer device receiving simultaneously all of the output signals from the series of filters and being able to be connected directly via an inverter switch to the intensity regulation means. 5. Listening training device comprising two hearing channels connected to a pair of headphones and connected in parallel, each including a cut-off filter for different sound frequencies and a switching means gradually switching on and off alternately each of the filters on each rising and falling edge of an input sound signal, characterized in that an automatic device for differential amplification of sound frequencies according to any one of the preceding claims is mounted in the circuit for the device so that the output signal from the automatic device constitutes the aforementioned input sound signal.