SE436533B - SET TO MUTE / ELIMINATE TRANSIENT SOUND AND TRANSIENT ELIMINATOR FOR IMPLEMENTATION OF THE SET - Google Patents

Description

â-ZGÛWZ-Z Until the 1810s has noise measurements and associated risk standards based on the dBA level where the presentation (the pointer) exhibits a time constant of about 35 ms. which roughly corresponds to the time constant of our whole subjective auditory sense, i.e. you meet what is subjectively experienced (heard) and not what is really damages. It is so that the mechanical part of our hearing organs (from the outer ear to the basilar membrane) has a much shorter time-constant, about 20-50 us. which explains that even sounds like not experienced particularly strongly (pJg.a., the long 'integration time in the brain) can mechanically damage the basilar membrane, when the instantaneous oscillation amplitudes can be very high even if the duration of the sound is so short that it is perceived as weak. Iranians and sounds with loud peak factors exhibit the above properties. This means that it is not only the weighted average sound energy level id8A level). but to a greater extent the properties of sound in the timetable, which reflects the harmful effects of a sound hearing.

Consequently, the human ear is not designed to withstand the transient sounds that our industrialized world has today creates. The people who suffered from a severe hearing loss usually some form of hearing aid is prescribed.

A hearing loss means increased "hearing threshold" ¿ However, the "comfort level" remains at the same level as in one normal ear. and may even in some cases even lie on a lower level. This reduces the dynamics (see Figure 5). The dashed area D represents the reinforcement need for relatively faint sounds. At a given frequency, arrow A shows the dynamics of a normal hearing ear and the arrow B dynamics at a hearing loss where the level of discomfort C has also decreased slightly.

The average amplification requirement can be, for example, '20 dB. This means that even loud sounds are amplified in such a hearing aid with 20 dB. which causes severe discomfort and a significant risk for further hearing damage. The result is that the patient lowers the amplification of the hearing aid. _which gives worse speech intelligibility. Then it is also a fact_ that electric 8200702-2 sound processing can never provide the same comfort and dry to directional hearing as without hearing aid (at the same sound pressure), it has been shown that 60-802 of the patients choose to put the appliance in the drawer. Modern hearing aids are looking reduce the problem of reduced dynamics by different compressor system consisting of, for example, an AGC (Automatic Gain Control). Psychoacoustic measurements have shown that the compressor devices show better speech intelligibility but have in return worse comfort than a conventional hearing aid without compressor function. This is because the compressors are frequency selective and need a certain integration time (attack time)> 0.5 ms, which means that the high amplitudes in the beginning of the transient passes through the hearing aid with a significant higher gain than is acceptable. At low sound levels, the compressor unit is also more noisy than one conventional hearing aid. one should also note in this context that the electronics in the final stage are overridden at strong moment levels, which entails. of distortion. partly that resonances in electronics elongate and amplify transients sound.

The harmful effects of transients and the discomfort experience that these give rise to can not be solved with known hearing aid technology.

It has long been known, but not used today. to transients are characterized by very high derivatives. Derivatives is the property of the schedule which reflects that amplitude spectrum in the Frequency Planet can not show. without the help of phase spectrum. which in turn is practically impossible to measure. Studies have shown that the discrimination between speech and transient sounds increase by 6-10 dB by deriving the audio signals. By integrating the half or the full-wave rectified derivative is further improved discrimination.

Hearing aids with various forms of transient elimination are then previously known. One of these is described, for example, in Danish Patent Publication No. 124439. It shows a hearing aid which % 2ÜQ '? 02-2 in addition to microphone, amplifier and headphone include Ken electronic circuit for differentiating incoming signal.

It has a number of disadvantages. Bl.a. breaks it the audio signal to the headphone completely upon detection of a transient which causes new transients to be created in the "flanks". Echo effects occur when reconnecting the earphone due to the transients being caused the interruption has significant reverberation I> 100 ms). The total the lack of sound during the interruption periods is perceived as unpleasant. This hearing aid must be considered a primitive construction and is in practice not usable.

Additional disadvantages are that a relatively high threshold value of the level of the transient signal, must be set due to discrimination problems between the "fundamental tone" .in speech (which is of transient nature) and the undesirable transients. The described hearing aid 7 also has 7 only instantaneous value increase. which requires very fast comparators, which in practice is almost impossible to achieve. Finally, it should also be pointed out that the couple is not years old retractable without the length of the sound interruption is once for all determined and can thus not be affected by that several transients occur, for example, just before the sound reconnected. This means that the reverberation can be troublesome. !! f; s g u I l sl! -V l Ia! IN The object of the present invention is to provide a method to attenuate / eliminate transient sounds. 'preferably at hearing aids intended for the hearing impaired or for hearing protection. whereby the derivative of the incoming audio signal is calculated as eliminates these disadvantages and this has been achieved: by that the mean derivative of the sound signal controls the attenuation / elimination of the harmful nuisances appearing in the audio signal transient sounds. In addition, the object of the invention is to: provide a transient eliminator for implementing the method and as year I operating safe and easy to use.

The transient eliminator shall. on a for the user comfortable 8-200702-2 5 way; eliminate / attenuate harmful / unpleasant transient sounds but still allow non-harmful sounds to pass. for example normal calls and which are characterized in that a converter is arranged in signal processing unit and set up to convert it from the derivative given the mean derivative ~ / differential to a control signal. which is arranged to control one proportionally therefore arranged dampers in such a way that harmful and unpleasant transient sounds appearing in the input to the microphone the audio signal is attenuated / eliminated. . . _.

The invention will hereinafter be described in one exemplary embodiments with reference to the accompanying drawings.

Figure 1 shows in a block diagram an invention according to the invention transient eliminator.

Figures 2a-c show in more detail various alternatives of a converter.

Figure 2d shows a connection example of an "ideal diode", Figure 3 shows an analog attenuator.

Figure 4a ~ c shows signal diagrams.

Figure S shows a diagram which describes the hearing frequency dependence in combination with hearing loss.

Description of execution exgmggl The one schematically shown in Figure 1. inventive, the transient eliminator comprises a microphone 1, which converts detected sounds into electrical signals. one signal processing unit 2 for processing incoming electrical signals and a headphone or speaker 3 for conversion of the finished electrical signals to sound.

The signal processing unit 2 consists of a plurality of circuit parts of which most of the years performed as integrated circuits in complementary HOS technology. This design guarantees a low power consumption which gives relatively long 820070242 operating periods between battery changes. This technology is also easy to integrate-to small dimensions which -is a lot important when it comes to hearing aids. These must be miniaturized for aesthetic and practical reasons. Microphones 1 is connected to a first amplifier 4 whose output signal a delay circuit 5 and a derivative 6 are supplied.

The delay circuit 5. which is performed in so-called CCD technology (Charge Coupled Devices). "Clocks" forward the information the entrance. to the output in step with the internal oscillator (not shown) frequency. To the output of the delay circuit 5 is an attenuator 7 connected whose attenuation is controlled by a converter 8. The delay circuit 5 is thus arranged to delay the input signal to the attenuator pair 7 so that a maximum attenuation can obtained at the highest passages of the transients. The derivative 5 is arranged to derive incoming audio signal and supply it resulting signal to converter 8.

CCD technology. as mentioned above. is a combination of analog and digital technology which makes AID and D / A converters as well as memories redundant. The technology is based on the analog signal is sampled into an analog sampling chain at a certain frequency.

The signal is output after N samples and the clock frequency is f a delay of tli sN / f is obtained. Time delays of electrical signals "can in themselves be performed in many different ways way. but when it comes to hearing aids, size and energy consumption is taken into account. For this reason, CCD technology has selected in this embodiment with which technique is optional delays from a few / ßs to several ms can achieved.

After the delay circuit 5 and the damper 7 are arranged partly a low-pass filter (LP filter) 8, whose cut-off frequency, for example can be set to 10 kHz, partly a signal control unit 10, with which the processed signal can be optionally adjusted with in terms of tone and volume. An output amplifier 11 is provided between the signal control unit 10 and the speaker 3.

Figure 2a shows, in more detail. the one in Figure 1 as one blocks showed. the converter 8. It includes. in a first 8200702-2 embodiment, a diode 13a connected in series with a first resistor 14. Diode 13a rectifies incoming signal and achieves, through its voltage drop. one initial threshold for the analog operating range of the damper 7. One capacitor 15 and a resistor 15 are further connected in parallel and connected to device ground. The resistor 14, the resistance in the diode 13a and the capacitor 15 form when the diode 13a is biased, an RC circuit whose time constant continues is called Tone _ The resistor 16 and the capacitor 15 form on similarly an RC circuit with a time constant Toçç. then the diode 13a is back tensioned.

Converter B also includes an externally adjustable control circuit 16 with which the damper 7 can fully or partially disconnected. In some environments where disturbing transients are very much unusual e.g. in a lecture hall. it may be appropriate to reduce the impact of the damper 7.

Figures 2b and 2c show alternative embodiments in which one A / D converter 19 years arranged Before the control circuit 18, and which A / D converter 19 is intended to convert the analog the signal to a digital signal. This digital signal is used For controlling a digitally controlled attenuator which can be used in instead of the previously mentioned analog damper T. The advantages using a digitally controlled attenuator (multiplying DAC). is that it is easy to make logarithmic, is easy to integrate and that it does not require any critical tuning.

In figure; 2c shows a converter 8 provided with an "ideal diode" 13b and a "true" integrator.An ideal diode 13b can, for example consist of, among other things, an operational amplifier and two diodes (see figure 2d). Because such an "ideal diode" exhibits low impedance at its output becomes the time constants Ton and Tar; about the same size. With this embodiment it is not obtained advantageous threshold level which was obtained when only a standard diode was used.

An analog type damper 7 according to the invention is shown in more detail in detail in Figure 3. It includes an amplifier 20. a 82Û07Û2-2 resistor 21 and a field effect transistor 22.

The converter 8 thus converts the derivative / differential to one. for the purpose adapted, control signal which controls the attenuator 7 which attenuator eliminates the audio signal / transient proportionally.

The control signal here consists of the "average derivative" of the sound signal.

By average derivatives' is meant that the derivative whole or half-wave rectified and applied. an integration grace.

The time constants in the integration network Ton and Tgfp do not need be the same size. In the exemplary embodiment described here (fig 2a. 2b) is fl mouth equal to 1-4 ms and Take significantly larger however, less is 200 ms (see dashed line B in Figure Ab). IN the working example according to figure '2c is T on = Tg {T which considered "true" integration. With proportional damping means here that the attenuation is a linear. or logarithmic. function of the potential across the capacitor 15 in the figures 2a-2c. By introducing a time constant in "attack". Ton = the value of the resistance of the diode 13a + the value of the resistor 16 multiplied by the value of the capacitor 15, much is obtained good discrimination between speech and harmful transients. One suitable value of Tgq has been found to be 1-4 ms at which time constant good discrimination has been obtained between speech and Harmful transients. Great care at Ton means at the same time that the delay time in the Delay Circuit 5 must be increased.

If a CCD delay line is used, this is not a problem. If would only be interested in attenuating very strong. hearing impaired. transients, Ton can be set approximately equal to 0 sec. With Tone = 1-4 ms, however, the hearing aids become significant more comfortable to wear without the need for more electronics introduced.

"Release time", i.e. the decrease in attenuation, which is determined by the time constant Tag = the value of the resistor 16 multiplied by the value of the capacitor 15. should be made significantly greater than Tbn, otherwise the control signal will contain a lot of ripple. The has also been shown to attenuate at the end of a transient should be slightly larger than the envelope on the derivative to give one pleasant sound image. Then the control signal B has a higher value than threshold level (marking C in Figure kb), the attenuation may be appropriate 8200702-2 be maximum. for example 30 dB.

Figures 4a-c show different diagrams where the vertical axes shows signal amplitude and the horizontal axes show time.

The curve illustrated in Figure 1a shows a typical appearance of a derived speech signal containing characteristic transients occurs at regular * intervals. These transients have relatively low amplitude but can still "trigger" one transient eliminator whose detection is only through threshold detection, i.e. even ordinary call tone can get one such hearing aid to break the sound to the ear. The risk of a normal call should activate the transient eliminator according to the present invention is very small as it is the mean of the derived signal which controls the attenuation of the signal.

Figure kb shows in more detail how a transient signal detected in the present invention. The dashed line B shows the potential across the capacitor 15 which increases with time when a transient with a plurality of overshoots is detected. It is in this case it is important that the time constant Ton is significantly less than time constant 1'0çç so that fast enough rise time obtained.

Figure hc shows a composite diagram with three horizontal ones time axes. This simplifies time comparison of the different shows the signals. The top one schematically shows the shape of a transient signal as it may appear after passed the amplifier 4 in the signal processing unit 2. On it the middle time axis shows the same signal after time delay in the time delay circuit 5, i.e. the signal supplied damper pair 7. The control signal from is displayed on the lowest time axis the converter 8 to the attenuator T, i.e. the middle derivative of it the incoming signal. This shows how the audio signal average derivatives are rapidly raised so that maximum attenuation is obtained in the attenuator 7 as the transient passes. To avoid unpleasant "eco-effects" caused by the reverberation of the transient are allowed the attenuation signal only to slowly decrease with time.

The invention is of course not limited to the above 3200702-2 10 described embodiment without a plurality of alternatives embodiments are conceivable within the scope of the claims scope of protection.

Claims (2)

8200702-2 PATENT REQUIREMENTS 1. Ways to attenuate / eliminate transient sounds. preferably for hearing aids intended for the hearing impaired or for hearing protection. wherein the derivative of the incoming audio signal is calculated, characterized therefrom. that the mean derivative of the sound signal controls the attenuation / elimination of the harmful / unpleasant transient sounds occurring in the sound signal. Transient eliminator for carrying out the method according to claim 1. i.e. for attenuating transient sounds. comprising a signal processing unit (2) which i.a. consists of a microphone (1). electrically connected to an amplifier (4). a derivative (6) and a delay circuit (S). both connected to the amplifier (4) and a speaker (3). kånneteckavn thereof. that a converter (8) is connected to the output of the derivative (B) and arranged to convert the instantaneous derivative emitted from the derivative (6) into an average derivative constituting a control signal. that a damper (7) is connected partly to the output of the delay circuit (5) and partly to the output of the converter (8). wherein the attenuator (7) is arranged to control the attenuation of the signal from the microphone (1) in proportion to the control signal from the converter (8). transmitted via the amplifier (4) and the delay circuit (5). in such a way that harmful / unpleasant transient sounds occurring in the sound signal applied to the microphone (1) are attenuated / eliminated.