EP0039012A1 - Device for converting dynamic pressure constituting a useful signal into an electric magnitude - Google Patents

Abstract

A device for the conversion of a dynamic pressure forming a useful signal, especially of the blowing pressure in a blowing converter for controlling the loudness of an electronic musical instrument, into an electric magnitude, altering in accordance with the value of the useful signal, as control signal, for example a voltage, has a dynamic pressure chamber, in which a membrane which responds sufficiently fast to the occurring frequencies and rise times of the useful signals is employed, which membrane is connected to a mechanoelectrical transducer with a circuit for the detection of the membrane movement and processing into the control signal. In such a device, in order to eliminate as far as possible the noise pulses located within the range of the useful signals, without impairing the response sensitivity of the membrane system, the dynamic pressure chamber (6), the membrane (7) and the transducer (10, 11) are designed so that they form an oscillatory system with a common resonance frequency, which is situated above the frequency range of the useful signals; in this case, the circuit exhibits a generator (12), generating voltage pulses or an alternating voltage in the range of the resonance frequency of the oscillatory system at least at zero dynamic pressure, for the excitation of the membrane (7) as well as an evaluation circuit for the detection of the alteration in resonance frequency as a result of the stressing of the membrane (7) by the useful signal, and a filter device (19) for the elimination of signals at least in the range of the resonance frequency of the oscillatory system. <IMAGE>

Description

The invention relates to a device for converting a dynamic pressure forming a useful signal, in particular the blowing pressure in a blowing transducer for volume control of an electronic musical instrument, into an electrical variable that changes with the value of the useful signal as a control signal, for example a voltage, with a dynamic pressure chamber in which a membrane which responds sufficiently quickly to the frequencies of the useful signal and their rise times is inserted, which is connected to a mechanoelectric converter with a circuit for detecting the membrane movement and processing into the control signal.

Such devices are known primarily in electronic musical instruments. Then they are permanent part of a keyboard wind instrument, which consists essentially of a wind converter and a keyboard. The keyboard wind instrument is connected to an electronic playback unit which generates the sound in accordance with the control by the buttons on the keyboard and the wind converter. By inserting different instrument modules, the sound of, for example, a trumpet, trombone, clarinet, oboe or the like can be reproduced practically true to life.

In contrast to the normal wind instrument, the wind transducer is no longer used to generate sound, but controls the dynamics of the sound specified by means of the keys, that is to say essentially its volume, depending on the intensity of the blowing pressure applied. For this purpose, the blow converter has a mouthpiece similar to a recorder, which merges inward into a dynamic pressure tube and into a blow-off tube. The blow-off pipe lets the air blown back into the open air, while a back pressure corresponding to the intensity of the blowing pressure is created in the back pressure pipe and the adjoining back pressure chamber.

The back pressure chamber is closed on one side by a membrane. This membrane is connected to a mechanoelectric converter, which converts the membrane movement into an electrical variable due to the dynamic pressure, which is processed by means of an electrical circuit into a control signal, for example a voltage, which behaves in accordance with the blowing pressure in order to control the playback unit. Coils or mirror systems that vibrate in accordance with the membrane movement are used as mechanoelectric converters in the magnetic field depending on the movement of the membrane, feed a light beam more or less strongly to a photocell, which converts the light into a proportional electrical quantity.

Compared to older devices, in which a sound sampled by a microphone was still generated, the dynamic pressure systems have the advantage that they do not emit sound themselves, are not very sensitive to moisture and have a large dynamic range. When using a membrane of low mass and high elasticity, a high sensitivity can also be achieved, so that back pressure changes with high rise times, such as occur in a staccato, or the relatively fast vibrations of a vibrato are processed well.

However, such a design of the membrane system has the disadvantage that the noise impulses which are unavoidable during blowing are also processed, at least in the frequency range for which the membrane is designed. However, this is also the area in which the dynamic pressure changes, i.e. the useful signals occur. The useful signals are thus falsified by the additional noise pulses in this frequency range, which leads to undesired dynamic changes in the reproduction.

Attempts have been made to reduce the influence of the pulse by means of mechanical damping, for example by using a harder membrane or by inserting an electronic low-pass filter into the electronic circuit. Although it was possible to improve the signal-to-noise ratio as a result, it did, however, make the useful signal read like the Noise pulses is also attenuated. In addition, the responsiveness of the system suffers, so that rapid changes in blowing pressure are only imperfectly recorded.

The object of the invention is to eliminate as far as possible the noise impulses in this area in a device of the type mentioned with a membrane system that is sufficiently sensitive to the useful signals that occur, without thereby impairing the response sensitivity of the membrane system.

This object is achieved in that the dynamic pressure chamber, membrane and transducer are designed in such a way that they form an oscillation system with a common resonance frequency which lies above the frequency range of the useful signals, the circuit at least providing a voltage pulse or an alternating voltage in the region of the resonance frequency of the oscillation system Has zero back pressure generating generator for excitation of the membrane and an evaluation circuit for detecting the change in resonance frequency due to the application of useful signals to the membrane and a filter device for eliminating signals at least in the range of the resonance frequency of the vibration system.

This solution is based on the idea, already part of the invention, of eliminating the influence of the noise pulses in the useful signal range by accelerating or decelerating them to a frequency that is outside the useful signal range by means of a resonance oscillation generated in the dynamic pressure chamber. There the noise impulses can simply be filtered out be without the useful signal is affected.

A resonance frequency lying outside the useful signal range is generated by excitation of the membrane by means of an electronic generator, the vibration system consisting of the dynamic pressure chamber, membrane and transducer being designed accordingly. The change in the resonance frequency by the application of the useful signal or the dynamic pressure to the membrane is used here for the formation of the control signal. The application of the useful signal affects the air density in the dynamic pressure chamber and the voltage of the membrane in such a way that the resonance frequency of the vibration system shifts in proportion to the intensity of the useful signal.

In an embodiment of the invention it is provided that the vibration system includes a defined rear space which is arranged on the side of the membrane facing away from the dynamic pressure chamber and whose resonance frequency is at least in the range of the resonance frequencies of the other parts of the vibration system. This back space dampens in particular the vibrations of the membrane lying above the useful signal range, so that falsifications from this range are largely eliminated.

The invention further provides that the resonance frequency of the vibration system is above five times the frequency range of the useful signal. In this way it is ensured that the noise pulses are lifted out of the useful signal range sufficiently. As far as the device for controlling an electronic musical instrument can be used a resonance frequency in the range of one kHz is expedient.

So that the movement of the membrane in the region of the resonance frequency is very pronounced, the resonance frequencies of the parts of the vibration system should be practically identical.

A low-pass filter with a cutoff frequency above the useful signal range but below the resonance frequency can be used as the filter device, for example.

For example, the following alternative solutions can be used for the detection of the change in resonance frequency to form a control signal. Thus, the circuit can be designed in such a way that the generator generates voltage pulses or an AC voltage of constant frequency and the evaluation circuit detects the respective resonance frequency by measuring the membrane amplitude and processes it into a corresponding control signal. In the simplest embodiment, such a circuit consists of a sine generator and an integrating rectifier, the converter being connected in parallel. Depending on the amplitude of the alternating voltage, a correspondingly high drive voltage is obtained which can be used for a reproduction device.

A second possibility is that the generator is switched to the resonance frequency in a control circuit for at least proportional readjustment of the generator frequency, the evaluation circuit detecting the respective generator frequency and processing it into a corresponding control signal.

A circuit in which the generator generates a square-wave voltage and the evaluation circuit detects the deformation of the square-wave pulses in the converter and processes it into a corresponding control signal has also proven to be well suited. The deformation of the rectangular pulses is brought about in that the membrane is no longer able to exactly follow the rectangular excitation in the region of the resonance frequency. The type of deformation, in particular its respective phase position, can then be processed into a control signal which is proportional to the distance between the resonance frequency and the generator frequency.

This can be done by providing a trigger circuit for converting the deformed square-wave pulses into a square-wave voltage, the trigger points of which are such that the square-wave voltage generated has a phase shift which is proportional to the respective deformation and which is processed to form the drive signal. The trigger points are expediently set such that the phase shift is 90 ° at a generator frequency that corresponds to the resonance frequency. The trigger points should be shortly before reaching the amplitude maximum or minimum of the deformed rectangular pulses. With this trigger circuit, the deformations can be converted into a phase-shifted square-wave voltage in a simple manner, the phase shift being proportional to the back pressure on the membrane.

For the detection of the phase shift can be a _P hare comparator is provided, which with the phase shift in a square-wave voltage comparison converts a clock ratio corresponding to the respective phase shift. An integrator can then be connected to the phase comparator for converting the comparison square-wave voltage into an analog voltage corresponding to the clock ratio, which may be used to an increased extent as a control signal. The integrator should at the same time contain the filter device with which the noise pulses synchronized to the resonance frequency are eliminated.

For the amplification, an amplifier can be provided behind the integrator, which has an exponential characteristic curve with such a characteristic that a larger change in the back pressure is required to achieve a certain increase in the control signal with increasing back pressure. This training is particularly recommended when using the device according to the invention as a blow converter.

To increase the dynamic range, the invention provides that the generator frequency can be voltage controlled and the generator is connected to the control signal in such a way that the generator frequency tracks the resonance frequency in a ratio of less than 1. The tracking ratio should expediently be adjustable, for example by means of a potentiometer. Due to this tracking, the distance between the generator frequency and the resonance frequency changes more slowly, so that the generator frequency remains longer in the range of the resonance frequency.

According to a further feature of the invention is a Stabilizing circuit for automatically adapting the generator frequency to the resonance frequency at zero dynamic pressure in at least one direction is provided. In this way, changes in the resonance frequency due to atmospheric pressure or moisture influences can be compensated. The stabilization circuit then ensures that the distance between the resonance frequency and generator frequency remains the same regardless of their absolute values.

The stabilization circuit should at least be able to push the generator frequency down again if there is a deviation from the resonance frequency. For this purpose, the stabilization circuit can consist of a comparator applied to the control signal, an integrator for forming a control voltage for the generator and a diode connected in between to prevent the discharge of the. Integrators exist, the threshold voltage of the comparator being at a control signal in which the generator frequency approximately matches the resonance frequency. The comparator should then have a high output level below its threshold voltage and the generator frequency should drop when the control voltage is raised. In this way, the generator frequency lying above the resonance frequency when the entire system is switched on can be reduced until they essentially match.

According to a further feature of the invention, it is provided that the stabilization circuit adjusts the generator frequency upwards when the resonance frequency deviates. Such a deviation usually arises during prolonged operation of the device, due to the effects of air pressure and moisture. With help the stabilization circuit, the generator frequency then follows the resonance frequency at zero dynamic pressure until they roughly match again, that is to say they have the distance value specified for zero dynamic pressure.

The adaptation of the generator frequency to the meanwhile increased resonance frequency can be done in combination with the circuit, which brings about an adjustment of the generator frequency to a lower resonance frequency, in that a second comparator, which also acts on the integrator, is provided in parallel with the first comparator threshold voltage above a portion of the _a nsteuerungs- signal is located, which may result from self-adjustment of the resonant frequency upward, said comparator switches to a low output level falls below its threshold, and that furthermore provided behind the second comparator a diode in the reverse direction and a limiting resistor . In this stabilization circuit, the integrator is discharged via the second comparator when the control signal at zero dynamic pressure lies between the threshold voltage of the first and the second comparator, which indicates that the resonance frequency is greater than the distance corresponding to the threshold voltage of the first comparator Generator frequency. Through the discharge process at the integrator, the resonance frequency increases again until the predetermined distance from the resonance frequency is given again.

The mechanoelectric converter is expediently designed as a coil attached to the membrane, which is arranged in a magnetic field. However, he can also be designed as a piezoceramic, capacitive or electromagnetic system.

To keep moisture away from the membrane, a moisture-absorbing filter should be placed in front of the dynamic pressure chamber. In a simple embodiment, this can be a pipe cleaner, for example.

Finally, the invention provides that a dynamic pressure tube is arranged in front of the dynamic pressure chamber and tapers towards the dynamic pressure chamber. Because of this tapering, the dynamic pressure tube is no longer part of the dynamic pressure chamber and can thus be shaped in any way without the resonant frequency of the dynamic pressure chamber being influenced thereby.

• Fig. 1 einen Blaswandler für ein elektronisches Musikinstrument mit einem Blockschaltbild der elektrischen Schaltung und
• Fig. 2 eine graphische Darstellung der Spannungsverläufe in der Schaltung gemäß Fig. 1.

In the drawing, the invention is illustrated in more detail using an exemplary embodiment. Show it:

• Fig. 1 is a blow converter for an electronic musical instrument with a block diagram of the electrical circuit and
• FIG. 2 shows a graphical representation of the voltage profiles in the circuit according to FIG. 1.

The blow converter 1 is shown in longitudinal section and is connected to an electrical circuit which is used to generate a control signal for an electronic playback unit. The blow converter 1 is part of a keyboard wind instrument (not shown here), the keys being used to control the respective pitch for the playback unit, while the blow converter 1 effects the dynamic control. essentially affects the volume. It also controls the playback unit, which then responds with a corresponding dynamic during playback.

The blowing transducer 1 essentially consists of a blowing piece 2 modeled on a flute mouthpiece and the blowing transducer body 3. Two channels run in the latter, namely the blow-off pipe 4, which runs obliquely downwards and opens out into the open again, which at all enables continuous blowing, and the dynamic pressure pipe 5, in which, depending on the blowing intensity, a more or less high dynamic pressure builds up. The latter narrows conically backwards.

The dynamic pressure tube 5 opens into a dynamic pressure chamber 6, which is closed off by an elastic membrane 7. It is designed in terms of its mass and elasticity so that it the useful signals occurring, al-; so that the blowing pressure and its changes can be processed, even with very rapid changes, such as those that occur with staccato or vibrato.

At the rear of the membrane 7 there is a rear space 8 which has a connection to the outside via a precisely defined bore 9, the bore 9 being dimensioned such that high frequencies of the membrane 7 are damped. In the back space 8, a permanent magnet lo is inserted, the north-south polarity of which is perpendicular to the surface of the membrane 7. On the membrane 7, a coil 11 is attached, which is located in the field of the permanent magnet lo.

Dynamic pressure chamber 6, membrane 7, rear chamber 8 and permanent magnet 10 and coil 11 are each designed that they have the same resonance frequencies at zero dynamic pressure. The resulting total resonance frequency depends on the volume of the dynamic pressure and rear space 6, 8, the volume of the dynamic pressure tube 5 can be neglected because of its conical design, the bore 9, the voltage and mass of the membrane 7 with coil 11 and their Inductance. It increases when the blowing pressure and thus the dynamic pressure increase because then the density of the air in the dynamic pressure chamber 6 and the voltage of the membrane 7 and the inductance of the coil 11 change. The same applies if the blowing pressure is weakened.

In the present case, the oscillation system is designed so that a resonance frequency is approximately 1 kHz, that is, far above the useful signal range, which in this case goes up to a maximum of 2oo Hz.

The coil 11 is connected to an electrical circuit in order to convert and process the movement of the membrane 7 and thus the coil 11 in the magnetic field when the blowing pressure is applied into a correspondingly behaving control signal, here a control voltage for the playback unit. The circuit is shown in a block diagram, the individual elements ("blocks") of which relate to individual circuits as are known per se under the respective names, so that their detailed explanation can be dispensed with.

The electrical circuit has a generator 12 which generates a square-wave voltage with a constant generator frequency which is in the range of the resonance frequency frequency of the previously described vibration system. The square-wave voltage passes through a low-pass filter 13 to round off the flanks and, via line 14 and the coil 11 connected to it, sets the diaphragm 7 and thus also the other parts of the vibration system into vibrations of a corresponding frequency.

The resonance vibrations generate standing waves in the dynamic pressure chamber 6, which accelerate or slow down the noise pulses occurring during blowing, depending on their frequency position, and thus "synchronize" with the resonance frequency. In this way, the noise pulses in the useful signal range are emphasized in the resonance frequency range, so that they can be filtered out more easily in the subsequent circuit.

The square-wave voltage of the generator 12 is deformed by the vibrations of the membrane 7 and thus the coil 11, because the membrane 7 and the coil 11 no longer follow the square-wave voltage properly due to the excitation in the resonance region, but instead execute sinusoidally shaped vibrations. The type of deformation depends on the distance between the generator frequency and the resonance frequency. If both are the same, the deformation is approximately symmetrical. If the generator frequency is smaller or larger than the resonance frequency, the deformation "moves" more according to the distance between the two frequencies to the ascending or descending branch of an amplitude.

This "migration" is brought about by differently applying diaphragm pressure to the diaphragm 7, since, as already described above, this results in a change in the resonance frequency. Then it runs fixed generator frequency away with the result that the deformation of the amplitudes of the generator voltage shift. The changes in the blowing pressure, which is supposed to bring about a corresponding change in the dynamics, therefore produce a proportional deformation of the amplitude of the generator voltage with the change in the resonance frequency caused thereby. The degree of deformation can then be processed into a control signal due to the proportionality to the blowing pressure.

For this purpose, a trigger 15 is initially provided, in which the deformed voltage pulses are converted back into a square wave voltage. The trigger 15 scans, as will be seen in more detail from FIG. 2, the deformed voltage pulses with an upper and a lower trigger point, the trigger points "migrating" in the phase direction when the blowing pressure changes with the deformation of the amplitudes. The trigger points are distributed in such a way that there is a phase shift between the square-wave voltage of the generator 12 and the square-wave voltage generated by the trigger 15, the amount of the phase shift being proportional to the deformations and thus ultimately proportional to the blowing pressure. When identity between the generator frequency and Rsonanzfrequenz a phase shift of 90 ° is set, if deviation of the resonance frequency up the phase shift is small and downwardly greater than 9 ₀ °.

The two square-wave voltages generated by the generator 12 and trigger 15 go via lines 16, 17 into a phase comparator 18. This forms a comparison square-wave voltage with one of the phase shifts Exercise corresponding clock ratio, ie the larger the phase shift, the shorter the square-wave pulses with a high level compared to those with a low level, the frequency being the generator frequency.

The comparison square-wave voltage is then converted into an analog voltage signal in an integrator 19. This integrator 19 is also designed as a low-pass filter and thus as a frequency filter. Its cut-off frequency here is 2oo Hz. Above this cut-off frequency, it acts as a barrier, so that the noise pulses synchronized to the resonance frequency of one kHz are filtered out, ie eliminated. The outgoing analog signal is therefore free from influences from the range above 2oo Hz and thus all noise pulses.

In a subsequent operational amplifier 20, the analog voltage is amplified to a drive voltage 21 that can be used by the playback device. The amplification does not have to be linear, but can also be done exponentially in such a way that a certain increase in the control voltage 21 towards higher blow pressures requires increasing blow pressure changes. In this way, extensive adaptation to the blowing pressure dynamic behavior in actual instruments can be achieved.

The upper limit of the dynamic range naturally has a limit, namely if the distance between the generator frequency and the resonance frequency has become too large due to very high blowing pressure, for further noteworthy deformations of the square-wave voltage of the generator 12 and thus cause a corresponding phase shift between this and the trigger square wave voltage. However, it can be increased if the generator frequency tracks the resonance frequency, but not as quickly as this. In this way, the resonant frequency of the generator frequency runs away more slowly, so that the frequency spacing, which limits the dynamic range, is only reached at higher blowing pressures.

The above-described tracking of the resonance frequency can be achieved in that the generator frequency is subjected to a voltage control, that is to say can be raised or lowered by changing a control voltage. So that this takes place synchronously with the resonance frequency, but only more slowly, the generator 12 can be connected to the output of the operational amplifier 20 via a connecting line 22 (shown in broken lines). Since the drive voltage 21 present there corresponds to the respective resonance frequency of the oscillation system in the blower converter 1, the generator frequency is tracked by the drive voltage 21, a potentiometer 23 in the connecting line 22 ensuring that the tracking is slowed down. By adjusting the potentiometer 23, the slowdown of the tracking can be adjusted as required.

The voltage controllability of the generator 12 can also be used for so-called zero point stabilization. Such a stabilization should be provided in order to keep the set distance between the generator frequency and the resonance frequency constant at zero dynamic pressure, that is to say without the diaphragm 7 being subjected to blowing pressure. or if the distance changes, the generator frequency can be traced back to the set distance regardless of the actual value of the resonance frequency. Such changes in distance can in particular be brought about by different air pressures and by the effects of moisture and have the consequence that the control voltage also changes, which is of course undesirable. In addition, changes in distance can occur when the blower converter 1 is switched on in that the capacitors of the circuit are initially discharged. Both can be eliminated by tracking the generator frequency to the specified distance from the resonance frequency.

For this purpose, a stabilization circuit is provided which automatically adjusts the generator frequency to the respective resonance frequency when the blowing pressure transducer 1 is switched on but not acted upon. It consists of two comparators 26, 27 connected in parallel lines 24, 25 to the control voltage 21, each with subsequent diodes 28, 29 with different blocking directions, and an integrator 3o after connecting the lines 24, 25, the high-resistance output of which is connected to the generator 12. This reacts when voltage is applied to input 31 so that the generator frequency increases when the voltage is reduced. A limiting resistor 32 is additionally installed in line 25.

The comparators 26, 27 have different threshold voltages and different behavior. The threshold voltage of the first comparator 26 is at a control voltage 21, which is slightly above that The resonant frequency corresponds to the generator frequency. If this threshold voltage is undershot, a high output level is produced in the first comparator 26.

The threshold voltage of the second comparator 27 is higher _i namely at a control voltage 21 which corresponds to a resonance frequency which is so far above the generator frequency that the threshold voltage is not exceeded due to self-adjustment of the resonance frequency and the control voltage 21 generated thereby. However, unlike the first comparator 26, the second comparator 27 has a low output level when the threshold voltage is undershot, and a high output level when it is exceeded.

• Beim Einschalten des Blaswandlers 1 ist die Spannung am Eingang 31 des Generators 12 noch relativ niedrig, weil der Integrator 3o bzw. dessen Kondensator noch entladen ist. Aufgrund dessen schwingt der Generator 12 mit einer Frequenz, die wesentlich oberhalb der Resonanzfrequenz liegt. Entsprechend wird die Rechteckspannung des Generators 12 in der Spule 11 derart verformt, daß die durch den Triger 15 bewirkte Phasenverschiebung über 90⁰ liegt. Bei einer so hohen Phasenverschiebung ist auch das Taktverhältnis der Vergleichsrechteckspannung nach dem Phasenvergleicher 18 derart, daß die daraus gebildete Analogspannung nach dem Integrator 19, die sich zudem wegen des dort ebenfalls vorhandenden Kondensators auch erst aufbauen muß, und damit die Ansteuerungsspannung 21 unterhalb der Schwellspannungen beider Komperatoren 26, 27 liegt. Der erste Komperator 26 führt somit . hohen Ausgangspegel, während der zweite Komperator 27 niedrigen hat.

The zero point stabilization automated in this way works as follows:

• When the blower converter 1 is switched on, the voltage at the input 31 of the generator 12 is still relatively low because the integrator 3o or its capacitor is still discharged. Because of this, the generator 12 vibrates at a frequency that is substantially above the resonance frequency. Accordingly, the square-wave voltage of the generator 12 is deformed in the coil 11 such that the Triger 15 caused by the phase shift is about 90 ^0th With such a high phase shift, the clock ratio of the comparison square-wave voltage after the phase comparator 18 is such that the analog voltage formed therefrom after the integrator 19, which also has to build up because of the capacitor also present there, and thus the drive voltage 21 below the threshold voltages of both Comparators 26, 27 is located. The first comparator 26 thus leads . high output level, while the second comparator 27 has low.

The comparator 26 now charges the integrator 3o or its capacitor because of the diode 28 switched in the forward direction, the limiting resistor 32 ensuring that the integrator 3o is charged faster than it discharges again via the diode 29 and the second comparator 27 could. When the integrator 3o is charged, the control voltage at the input 31 of the generator 12 also rises, causing its frequency to decrease accordingly. As a result of the approximation to the instantaneous resonance frequency, the deformation of the square-wave voltage moves in the direction of lower phase shifts to the square-wave voltage generated in trigger 15, as a result of which the control voltage 21 increases until it has reached the threshold voltage of the first comparator 26.

The generator frequency is then just above the resonant frequency and the phase shift slightly above 9 ₀ °. The first comparator 26 then switches to a low level so that the integrator 3o is no longer charged.

However, this discharges again immediately via the limiting resistor 32, the diode 29 and the second comparator 27, which is switched to a low level, so that the control voltage for the generator 12 drops and the frequency thereof increases again. This, in turn, continues until the control voltage 21 has dropped so far as a result of the generator frequency rising relative to the resonance frequency that the first comparator 26 switches back to a high level. so that the integrator 3o is recharged, so the generator frequency drops again. The entire system therefore oscillates around the threshold voltage of the comparator 26, as a result of which the generator frequency is kept practically constant at a value which is somewhat above the resonance frequency.

If the diaphragm 7 is now subjected to a useful signal, that is to say the blowing pressure, the resonance frequency of the vibration system is shifted far upward, as a result of which the control voltage 21 also increases accordingly. In any case, this increase is so high that the threshold voltage of the second comparator 27 is exceeded. This then switches to a high output level, which is blocked by the diode 29, but on the other hand also prevents the integrator 3o from being discharged. Since the other diode 28 likewise makes discharge impossible, the control voltage of the integrator 3o and thus the generator frequency remain constant during the example of the device. An adjustment of the generator frequency, which would then be undesirable, is prevented in this way, unless the tracking already described above via the connecting line 22 and the potentiometer 23 is provided. In both cases, the value of the control voltage 21 is determined by the distance between the resonance frequency, which is dependent on the respective blowing pressure, and the generator frequency, which is either kept constant or slower.

It also follows from this that the dynamic range of the blow converter 1 lies above the threshold voltage of the second comparator 27. Underneath drive voltages 21 are for the playback device filtered out so that they have no influence on the dynamics.

During a break, the resonance frequency drops again due to the lack of blowing pressure, but often no longer up to the initial value to which the generator frequency was set. The resonance frequency may have shifted upwards, in particular due to moisture influences. This is undesirable because higher control voltages 21 would then result with a certain blowing pressure than at the beginning.

However, since the threshold voltage of the second comparator 27 is selected to be so high that the control voltage 21 of a resonance frequency adjusted in this way is normally always lower at zero blowing pressure, the second comparator 27 switches back to a low level during a pause, so that the integrator 3o is above it begins to discharge. The control voltage at the input 31 of the generator 12 thus drops, as a result of which the generator frequency increases accordingly until it is again somewhat above the resonance frequency. Here, namely, the control voltage 21 has again reached a value due to the increasing phase shift, which causes the first comparator 26 to switch to a high level, so that the integrator 3o is recharged. The phase is then reached again in which the system oscillates around the threshold voltage of the first comparator 26, that is to say the generator frequency is practically kept at the same value.

Fig. 2 shows in its sub-figures a, b and c the deformation of the square wave voltage of the generator 12 in the Coil 11 and the resulting phase shift of the square-wave voltage generated by the trigger 15. In all sub-figures, the generator voltage 33 at the output of the generator 12 is at the top, in the middle the voltages 34a, b, c deformed in the coil 11 in accordance with the respective distance between the generator and resonance frequency, and at the bottom the associated trigger voltages 35 a, b, c applied to each other at the same time. The dash-dotted vertical lines separate the individual sub-figures 2a, 2b and 2c.

Auxiliary lines are drawn to represent the voltages 34a, b, c deformed in the coil 11, namely a center line and two outer lines at the top and bottom to indicate the maximum and minimum amplitudes and two inner lines on which the upper lines indicated by slashes and lower trigger points 36, 37. As can be seen, the trigger 15 is set so that it switches shortly before reaching the amplitude maxima and minima. This is done inversely, i.e. before the amplitude maximum is reached, it switches to low trigger output voltage and vice versa.

In Fig. 2a, the resonance frequency is greater than the generator frequency 33. This corresponds to a Blasdruckbeaufschlagung the membrane 7. The deformation of the voltage 34a is such that the phase shift is smaller than 38 9 ₀ °. This phase shift becomes even smaller with increasing blowing pressure.

2b, the resonance frequency is identical to the generator frequency 33. The result is a deformed one Voltage 34b, which is practically sinusoidal and therefore symmetrical. The phase shift 38b then has the exact value of 9. ₀ °.

In FIG. 2 c, the phase shift 38 c has increased to over 90 ° due to a corresponding deformation of the voltage 34 c, because the resonance frequency is lower than the generator frequency 33. These conditions are present in the circuit according to the exemplary embodiment when the blowing converter 1 is not subjected to blowing pressure, that is to say at zero dynamic pressure.

Claims (13)

1.Device for converting a dynamic pressure forming a useful signal, in particular of the blower pressure in a blower converter for volume control of an electronic musical instrument, into an electrical variable which changes with the value of the useful signal as a control signal, for example a voltage, with a dynamic pressure chamber in which one the occurring frequencies and rise times of the useful signals responding membrane is used sufficiently fast, which is connected to a mechanoelectric converter with a circuit for detecting the membrane movement and processing in the control signal, characterized in that dynamic pressure chamber (6), membrane (7) and converter ( lo, 11) are designed so that they are a vibration Form a system with a common resonance frequency, which lies above the frequency range of the useful signals, the circuit generating a voltage pulse or an alternating voltage in the range of the resonance frequency of the oscillation system, at least in the case of a generator (12) generating zero back pressure, for exciting the membrane (7) and an evaluation circuit for detection the change in resonance frequency due to the application of the useful signal to the membrane (7) and a filter device (19) for eliminating signals at least in the region of the resonance frequency of the vibration system. 2. Apparatus according to claim 1, characterized in that the vibration system includes a defined on the side of the diaphragm (7) facing away from the dynamic pressure chamber (6), defined rear space (8), the resonance frequency of which is at least in the range of the resonance frequency of the other parts of the vibration system . 3. Apparatus according to claim 1 or 2, characterized in that the resonance frequencies of the parts of the vibration system are practically identical. 4. Device according to one of claims 1 to 3, characterized in that the filter device (19) is designed as a low-pass filter with a cutoff frequency above the useful signal range but below the resonance frequency. 5. Device according to one of claims 1 to 4, characterized in that the generator (12) generates a square wave voltage (33) and the evaluation circuit Deformation of the rectangular pulses in the transducer (lo, 11) is detected and processed into a corresponding control signal (21). 6. The device according to claim 5, characterized in that a trigger circuit (15) for converting the deformed square wave pulses (34) into a square wave voltage (35) is provided, the trigger points (36, 37) are such that the square wave voltage generated (35) compared to the deformed one has a phase shift (38) proportional to the respective deformation, which is processed into the actuation signal (21). 7. The device according to claim 6, characterized in that a phase comparator (18) for converting the phase shift (38) of the two square-wave voltages (33, 35) is provided in a comparison square-wave voltage with a clock ratio corresponding to the respective phase shift (38) and in that the phase comparator (18) is followed by an integrator (19) for converting the comparison square-wave voltage into an analog voltage corresponding to the clock ratio, which can optionally be used increasingly as a control signal (21). 8. The device according to claim 7, characterized in that the integrator (19) is followed by an amplifier (2o), which has an exponential characteristic with such a characteristic that to achieve a certain increase in the control signal (21) with increasing back pressure a larger Back pressure change is required. 9. Device according to one of claims 4 to 8, characterized in that the generator frequency is voltage controlled and of the generator (12) is engaged with the drive signal (21) so connected that the generator frequency of the resonance frequency in a ratio less is tracked as a 1, wherein the _N achführungsverhältnis is optionally adjustable. lo. Device according to one of claims 1 to 9, characterized in that a stabilizing circuit is provided for automatically adapting the generator frequency to the resonance frequency at zero back pressure in at least one direction. 11. The device according to claim lo, characterized in that the stabilizing circuit from a comparator (26) applied to the control signal (21), an integrator (3o) for forming a control voltage for the voltage-controllable generator (12) and an interposed diode (28 ) to prevent the integrator (3o) from discharging, the threshold voltage of the comparator (26) being at a control signal (21) in which the generator frequency roughly corresponds to the resonance frequency. 12. The device according to claim 11, characterized; that the comparator (26) has a high output level below its threshold voltage and the generator frequency drops when the control voltage is raised. 13. Device according to claims 11 and 12, characterized in that parallel to the first comparator (26), a second, also on the integrator (3o) acting comparator (27) is provided, the threshold voltage is above a range of the control signal (21) that is self-ver Position of the resonance frequency can result upwards, this comparator (27) switches to a low output level when it falls below its threshold voltage, and that behind the second comparator (27) a diode (29) in the blocking direction and a limiting resistor (32) is provided.

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