Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS
  • H04R1/00—Details of transducers, loudspeakers or microphones
  • H04R1/005—Details of transducers, loudspeakers or microphones using digitally weighted transducing elements
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS
  • H04R19/00—Electrostatic transducers
  • H04R19/04—Microphones

Definitions

• the invention relates to a method according to the preamble of claim 1 and to a sound receiving arrangement according to the preamble of claim 19.
• the object of the invention is to provide a method and a sound receiving arrangement in order to enable a direct conversion of an acoustic signal acting on the sound receptor of a sound receiver into digital information and thereby to meet the requirements with regard to dynamic range, noise and sufficient quantization.
• the invention is based on the idea of maintaining the principle of the capacitive converter for a “real” digital microphone, which principle has so far been unsurpassed in terms of dynamic range and noise behavior.
• the well-known and mature technology of the capacitive converter can thus be fully adopted.
• the capacitive transducer is included in a digitizing conversion process in such a way that the receptor (e.g. condenser membrane), on which the acoustic signal acts as sound pressure, is not deflected in a manner proportional to the signal strength, but approximately according to the invention by a counter-sound signal or by a counterforce is held at rest.
• the counter signal is derived from the controlled variable of a control loop which contains the sound receiver as a component, the controlled variable containing the information about the acoustic signal.
• Fig. 1 is a block diagram of a first embodiment of a digital signal
• Fig. 2 is a block diagram of a second embodiment of a digital signal
• Fig. 3 is a block diagram of a third embodiment of a digital signal
• Fig. 4 is a block diagram of an embodiment of an analog microphone according to the invention.
• the reference symbol 1 denotes a sound generator and the reference symbol 2 denotes a sound receiver, which can be the same or different in location and can be based on the same or different electro-acoustic transducer principles. It is essential that two oppositely directed, equally large forces act simultaneously on the sound receptor of the sound receiver 2, namely the force of the incident useful sound (acoustic signal) and the counterforce of a counter signal generated by the sound generator 1, which has the effect desired according to the invention that the sound receptor despite Exposure of the acoustic signal is largely held in its rest position. Every smallest deviation of the receptor from its rest position in the positive and negative direction can be evaluated directly as digital information "one" or "zero". The digital information thus arises directly at the receptor of the sound receiver 2.
• the sound generator 1 can generate a counter signal which is simultaneous with the acoustic signal incident on the sound receiver and is of the same magnitude as the acoustic signal
• the counter signal is derived from the controlled variable of a sufficiently fast control circuit, which the sound generator 1 and the sound receiver 2 as Contains ingredient.
• the acoustic transit time or the structural distance between sound generator 1 and sound receiver 2 decisively determine the achievable frequency bandwidth of the control loop and should therefore be as small as possible so that the control loop operates stably in the entire hearing frequency range.
• sound generator 1 and sound receiver 2 are of the same location, which means that the sound receptor (eg membrane) of the sound receiver 2 and the sound generator of the sound generator 1 are combined in a common component.
• sound generator 1 and sound receiver 2 have, for example, a common membrane. It is also advantageous if sound generator 1 and sound receiver 2 operate according to different electroacoustic transducer principles in order to avoid an undesired electrical bypass and thus crosstalk.
• the sound generator 1 can be implemented electrostatically or magnetically and the sound receiver 2 as a capacitor of a high-frequency resonant circuit.
• FIGS. 1 to 3 differ in how the digital information generated directly at the receptor of the sound receiver 2 is evaluated and how the control loop is designed.
• the control loop is designed in the form of a modified delta-sigma modulator, as described, for example, in the magazine Audio Professional, issue 3/4, 1995, pages 59 to 65. 1 as well as in all other FIGS. 2 to 4, the sound receiver 2 is implemented as a capacitor of a high-frequency resonant circuit with resonant circuit inductance 22.
• the incoming diaphragm first deflects the common diaphragm of the sounder / receiver combination 1/2 and detunes the HF resonant circuit due to the changing capacitance.
• the resonant circuit inductor 22 is part of a high-frequency demodulator 3 (phase or amplitude demodulator), which is indicated by an RF oscillator 37 and a demodulator diode 36 in the block of the RF demodulator 3.
• a long control characteristic curve, as is required in conventional condenser microphones, is not required for the HF demodulator 3, since the only thing that matters is that the deviations of the diaphragm of the sound transmitter / receiver combination 1/2 in the positive or negative direction from their idle position are correct to recognize.
• the RF demodulator 3 can therefore be designed with a very high sensitivity, which is of considerable advantage for the noise and dynamic behavior of the overall system.
• the output signal of the RF demodulator 3 is fed to a comparator 4, the output signal of which electrically represents the digital information generated directly at the receptor (membrane) of the sound receiver 2, ie the deviation of the membrane position in a positive or negative direction as an "O" signal or " 1 "signal.
• This digital signal represents a 1-bit word.
• the output signal of the comparator 4 controls the counting direction (up / down input) of a 4th -step counter 5, the clock input CLK of which is clocked by a clock generator 9 (CTL Network) with, for example, 64 times the sampling frequency (FS) of 48 kHz which is common in the digitization of audio signals.
• CTL Network clock generator 9
• the 4-bit word at the parallel outputs of the counter 5 is supplied on the one hand to a digital filter 10 and on the other hand to a 4-bit digital / analog converter 6.
• the 4-bit signal converted into an analog signal is routed through single or multi-stage integration and difference formation by means of a chain of difference and integration stages 7.1 to 7.N in order to statistically distribute the bit patterns created in the quantization process in the frequency transmission range and that Focus quantization noise in a frequency range above the hearing frequency range.
• the signal which arises at the end of the chain of differential and integrating stages 7.1 to 7.N is amplified in a driver amplifier 8, the output signal of which drives the sound generator 1.
• the control loop consisting of blocks 2, 3, 4, 5, 6, 7.1 to 7.N., 8 and 1 is thus closed. As already mentioned, due to the effect of this control loop, the forces acting on the membrane due to the incident sound are neutralized.
• the digital filter 10 at whose parallel inputs A, B, C and D the 4-bit word from the parallel outputs of the counter 5 is present, is clocked with the same clock frequency (3.072 MHz) as the counter 5.
• the filter 10 serializes the parallel 4-word, whereby due to the 64-fold oversampling a 20-bit signal 12 with the sampling frequency of 48 kHz at the output of the digital filter. 10 occurs.
• An FIR filter is preferably provided as the digital filter 10. In the case of digital filtering, the noise components in the 4-bit output signal of the counter 5 located above the listening area are also effectively suppressed.
• serial digital 20-bit output signal 12 can also be converted into any other data formats.
• a format converter 11 is indicated in FIG. 1, the serial input SER.IN of which the signal 12 is supplied.
• the clock input CLK and another, which serves the word synchronization FRM CTL input are connected to the clock 9.
• the optionally provided format converter 11 generates a parallel output signal at its multiple outputs, the first of which is designated with LSB (corresponding to the least significant bit) and the last with MSB (corresponding to the most significant bit).
• the format converter 11 has an output AES / EBU for an AES / EBU interface and a free output OTHER FORM for a selectable other digital format.
• the control circuit can be implemented as a 1-bit converter, as a modification of the embodiment according to FIG. 1, so that the counter 5 eliminates the output of the comparator 4 and connects it directly to the chain of differential and integrating stages 7.1 to 7.N.
• the modulated RF oscillation does not first have to be demodulated analogously and then digitized (using an RF demodulator 3 with a comparator 4 connected downstream), but can, as FIGS. 2 and 3 show, directly in a stage 30 into a (digital) 1-bit signal can be converted.
• the stage 30 contains a limiter amplifier or comparator 31, which converts the phase-modulated RF oscillation at the oscillating circuit coil 22 directly into a rectangular signal with a digital logic level.
• phase-locked RF clock oscillator 33 which excites the resonant circuit, consisting of the capacitive sound receiver 2 and the resonant circuit coil 22, via the coupling capacitor 35 and is synchronized by the clock oscillator 9 if necessary.
• a digital phase comparison between the digitized RF oscillation and the RF clock oscillator 33 immediately produces the 1-bit signal sequence which carries the information of the sound receptor deflection from the rest position. In the considered embodiment according to FIGS. 2 and 3, this function is performed by a D flip-flop.
• the 1-bit signal is now read into the digital filter 10 with the necessary oversampling, from which the desired quantization of the useful signal results, and is fed to the differential and integrating stages 7.1 to 7.N.
• the embodiment according to FIG. 3 differs from the embodiment according to FIG. 2 in that the difference and typical for a delta-sigma converter Integrating stages 7.1 to 7.N with digital filter 10 are omitted and replaced by a high-resolution analog-digital converter 50 (in the example considered as a counter) and a high-resolution digital-analog converter 60, so that the control loop is closed again.
• the digital output signal 120 is produced directly at the output of the analog-to-digital converter 50, which is shown as a serial signal in the example considered and which can be converted in the format converter 11 in the manner described above into digital output signals of any other format.
• FIGS. 1 to 3 shows, as it were, a "waste product" of the digital microphone according to FIGS. 1 to 3, an improved analog microphone, in which, in comparison to the circuit arrangement according to FIG. 1, only the sound receiver-sound transmitter combination 1/2, the HF demodulator 3 and the driver amplifier 8 have been retained.
• the demodulated RF signal (with a very small amplitude) at the output of the RF demodulator 3 is amplified only by means of an amplifier 20 in order to form an analog microphone output signal 23 of high quality.
• the driver signal for driving the sound generator 1 is also obtained in the amplifier 9 from the output signal 23.
• the analog output microphone output signal 23 can be converted into a digital signal by means of a conventional analog-digital converter 21, which is shown as a serial signal in the example shown.
• the advantages of the "real" digital microphone according to FIGS. 1 to 3 remain the advantages with regard to the low sound receptor deflection and the associated improvements described at the outset with regard to linear and non- linear distortions and sensitivity are obtained if the amplifier 20 is designed with a sufficiently large gain. For example, with a gain factor 100 of the amplifier 20, the membrane deflection of the sound receiver 2 and the electrical output signal of the sound receiver 2 are reduced by the corresponding amount.

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• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Acoustics & Sound (AREA)
• Signal Processing (AREA)
• Circuit For Audible Band Transducer (AREA)
• Investigating Or Analyzing Materials By The Use Of Ultrasonic Waves (AREA)
• Electric Clocks (AREA)
• Communication Cables (AREA)

Applications Claiming Priority (3)

Publications (2)

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ID=7789558

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Cited By (1)

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• 1996
  • 1996-03-27 DE DE19612068A patent/DE19612068A1/de not_active Withdrawn
• 1997
  • 1997-01-14 US US09/155,350 patent/US6697493B1/en not_active Expired - Fee Related
  • 1997-01-14 EP EP97900600A patent/EP0890291B1/fr not_active Expired - Lifetime
  • 1997-01-14 DE DE59704535T patent/DE59704535D1/de not_active Expired - Fee Related
  • 1997-01-14 JP JP53396297A patent/JP3534778B2/ja not_active Expired - Fee Related
  • 1997-01-14 AT AT97900600T patent/ATE205354T1/de not_active IP Right Cessation
  • 1997-01-14 WO PCT/EP1997/000131 patent/WO1997036454A1/fr not_active Ceased
  • 1997-01-14 DK DK97900600T patent/DK0890291T3/da active

Non-Patent Citations (1)

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