EP0890291B1 - Process and arrangement for converting an acoustic signal to an electrical signal - Google Patents

Abstract

To facilitate direct conversion to digital form of an acoustic signal acting on the acoustic receptor of an acoustic receiver while satisfying requirements of dynamic range, noise and adequate quantization, the following is proposed: the acoustic receptor should be exposed to a counter-signal when the acoustic signal acts on it in such a way that the acoustic receptor is largely maintained in its rest state despite the action of the acoustic signal. The counter-signal is derived from the control variable of a control circuit which is a component of the acoustic receptor. The control variable contains the information on the acting acoustic signal. Any deviation of the receptor from its rest state immediately generates a digital "nought" or "one."

Description

The invention relates to a method according to the preamble of claim 1 and a sound receiving arrangement according to the preamble of claim 19.

The efforts so far to create a "real" digital microphone without analog Building an intermediate step did not go beyond theoretical considerations. These considerations are based on the sound receptor (e.g. membrane) an electroacoustic sounder in terms of its position or movement to be measured optically or by means of ultrasound, for example by evaluating Interference patterns or of runtime effects, the digitization of measured information etc. done by a counting process. Such a process is given, for example, in GB-A-2 077 074. The sound is over two Sound receptors recorded, which acoustically in the direction of the incident sound are connected in series. The emitted by both sound receptors Signal voltages are offset by an amount that results from the sound propagation time between the two sound receptors arranged at a certain distance. By comparing and digitizing these two signals, a 1-bit DPCM signal is created which generates an up-down counter for conversion into a bit parallel Digital signal is supplied.

With the purely electrical conversion of analog audio signals into a corresponding one Digital signal are now available converters that special Requirements for converting audio signals are already sufficient. The are high resolution, linearity and low self-noise. These properties are achieved in particular by so-called sigma-delta converters, such as these for example from US-A-5 181 032 and US-A-5 191 332 are known. Both known sigma-delta converter, the audio signal is fed into a control loop, wherein the feedback feedback signal is via a 1-bit or a conventional multi-bit AD converter and a corresponding back converter to be led. In the generated digital 1-bit or multi-bit data stream Analog audio signal information through the temporal relationship of the digital 0/1 states shown. This is done using digital filtering and reformatting desired digital output signal obtained. Such a control loop system provides a modulator synchronized by a supplied clock, whereby by Splitting the information in the modulator into several signal paths and different signal treatment, favorable noise and resolution properties can be achieved.

All known converters for the direct generation of a digital signal from a however, acoustic input signals are unsuitable for studio microphones because they in terms of dynamic range, noise and sufficient quantization with analog Studio microphones can't keep up.

In contrast, the object of the invention is a method and a Sound receiving arrangement to specify a direct conversion from one to the Sound receptor of a sound signal acting acoustic signal in a digital To enable information and the requirements regarding dynamic range, Noise and sufficient quantization to meet.

This object is achieved by the characterizing features of the independent claims 1 and 19 solved.

Advantageous refinements and developments of the invention Procedures result from subclaims 2 to 18.

Advantageous refinements and developments of the invention Sound receiving arrangement result from subclaims 20 to 36.

The invention is based on the consideration that has so far been made with regard to dynamic range and noise behavior unsurpassed principle of the capacitive converter for a to keep "real" digital microphone. The well-known and mature Capacitive converter technology can thus be fully adopted. The capacitive transducer is transformed into a digitizing process included that the receptor (e.g. condenser membrane) on which the acoustic signal acts as sound pressure, not in one of the signal strength is deflected proportionally, but according to the invention by a Counter-sound signal or held almost at rest by a counterforce becomes. The counter signal is derived from the controlled variable of a control loop, which contains the sound receiver as a component, the controlled variable being the Contains information about the acoustic signal. As a result of the persistence of the receptor in its reverberant rest position are known to Condenser microphones characteristic curve errors, which depend on the position of the receptor depend and lead to signal distortions, as well as mechanical natural resonances of the receptor, which determines the frequency response and the pulse behavior of the electrical Affect output signal, practically no longer effective. Furthermore are Measures for passive attenuation of the receptor, as they are known Condenser microphones required for linearization are accepted a deterioration in sensitivity, practically no longer in the invention required so that the sensitivity of a trained according to the invention Converter is significantly improved. It is essential that the only minor Residual deflections of the receptor can be evaluated in such a way that only information about the direction of the deviation from the rest position arises and this information is represented as digital "zero" or "one". This means that the comparator function as a directly on the sound receptor elementary function of each analog-digital conversion process without an analog intermediate signal obtained from the sound receiver is needed.

Fig. 1

ein Blockschaltbild einer ersten Ausführungsform eines digitalen Mikrofons nach der Erfindung;

Fig. 2

ein Blockschaltbild einer zweiten Ausführungsform eines digitalen Mikrofons nach der Erfindung;

Fig. 3

ein Blockschaltbild einer dritten Ausführungsform eines digitalen Mikrofons nach der Erfindung, und

Fig. 4

ein Blockschaltbild einer Ausführungsform eines analogen Mikrofons nach der Erfindung.

The invention is explained in more detail with reference to the exemplary embodiments shown in the drawings. It shows:

Fig. 1

a block diagram of a first embodiment of a digital microphone according to the invention;

Fig. 2

a block diagram of a second embodiment of a digital microphone according to the invention;

Fig. 3

a block diagram of a third embodiment of a digital microphone according to the invention, and

Fig. 4

a block diagram of an embodiment of an analog microphone according to the invention.

In Figures 1 to 4, the reference numeral 1 is a sound generator and with the Reference numeral 2 denotes a sound receiver, which is the same or different locations can be and on the same or different electro-acoustic Converter principles can be based. It is essential that the sound receptor of the Sound receiver 2 two oppositely directed, equally large forces simultaneously act, namely the force of the incident useful sound (acoustic signal) and the counterforce of a counter signal generated by the sounder 1, which the invention has the desired effect that the sound receptor despite Exposure of the acoustic signal is largely kept in its rest position. Every smallest deviation of the receptor from its rest position in positive and negative direction can be immediately as digital information "one" or "zero" evaluate. The digital information is created directly at the receptor of the Sound receiver 2.

So that the sounder 1 can generate a counter signal which is simultaneous with the there is an acoustic signal incident on the sound receiver and the same amount As large as the acoustic signal, the counter signal becomes a controlled variable sufficiently fast control circuit derived, the sounder 1 and the Contains sound receiver 2 as a component. The acoustic runtime or the structural The distance between sound generator 1 and sound receiver 2 largely determines the achievable frequency bandwidth of the control loop and should therefore, if possible be small so that the control loop works stably in the entire hearing frequency range. For the practical implementation, it is therefore favorable if sound generator 1 and Sound receiver 2 are the same location, which is equivalent to the fact that the sound receptor (e.g. membrane) of the sound receiver 2 and the sound generator of the sound generator 1 are combined in a common component, i.e. sound generator 1 and Sound receiver 2, for example, have a common membrane. It is furthermore favorable if sound generator 1 and sound receiver 2 according to different Electroacoustic transducer principles work to remove an unwanted electrical Avoid bypass and thus crosstalk. For example, the Sounder 1 electrostatic or magnetic and the sound receiver 2 as Capacitor of a high-frequency resonant circuit can be realized.

The exemplary embodiments shown in FIGS. 1 to 3 differ in how the digitally generated directly at the receptor of the sound receiver 2 Information is evaluated and how the control loop is designed.

In the embodiment according to FIG. 1, the control loop is in the form of a modified one Delta-sigma modulator, such as that in the Journal Audio Professional, Issue 3/4, 1995, pages 59 to 65.

The sound receiver 2 is in Fig. 1 as in all other figures 2 to 4 as Capacitor of a high-frequency resonant circuit with resonant circuit inductance 22 realized. The common membrane of the Sounder-sound receiver combination 1/2 first deflected and detuned the RF resonant circuit due to the changing capacitance. The resonant circuit inductance 22 is part of a high-frequency demodulator 3 (phase or Amplitude demodulator), which by an RF oscillator 31 and Demodulator diode 32 is indicated in the block of the RF demodulator 3. A Long control characteristic, as is the case with conventional condenser microphones is not required for the RF demodulator 3, since it is only it depends on the deviations of the membrane of the sound transmitter-sound receiver combination 1/2 in a positive or negative direction from its rest position recognizable with the correct sign. The RF demodulator 3 can therefore be very high Sensitivity are designed, which is of considerable advantage for the noise and Dynamic behavior of the overall system is.

The output signal of the RF demodulator 3 is fed to a comparator 4, whose output signal is at the receptor (membrane) of the sound receiver 2 directly represents digitally generated digital information, i.e., the Deviation of the diaphragm position in a positive or negative direction as an "O" signal or "1" signal. This digital signal represents a 1-bit word. To make this a multi-bit word, in the example shown a 4-bit word generate, the output signal of the comparator 4 controls the counting direction (Up / Down input) of a 4-stage counter 5, the clock input CLK of one Clock 9 (CTL Network) with, for example, 64 times that at Digitization of audio signals with a standard sampling frequency (FS) of 48 kHz becomes. As a result of this oversampling with 64 x 48 kHz (= 3.072 MHz) the temporal resolution of the 1-bit word by the ratio of "zeros" and "Ones" is displayed, increased according to the amount of oversampling. To the Parallel outputs A, B, C and D of the counter 5 creates a 4-bit signal that the Information about the amplitude of the acoustic incident on the sound receiver 2 Contains signals. However, the quantization of the information does not only result amplitude-oriented (4-bit word). As a result of oversampling the 1-bit word on When the counter 5 is received, the quantization of the information also results in a time-oriented manner according to the temporal relationship between different 4-bit words.

The 4-bit word on the parallel outputs of the counter 5 becomes one digital filter 10 and on the other hand a 4-bit digital / analog converter 6 fed. The 4-bit signal converted into an analog signal is or multi - stage integration and difference formation using a chain of Difference and Intergierstufen 7.1 to 7.N passed to the in the quantization process resulting bit patterns statistically in the frequency transmission range distribute and the quantization noise in a frequency range above the Focus hearing frequency range. That at the end of the chain of difference and Intergierstufen 7.1 to 7.N resulting signal is in a driver amplifier 8 amplified, whose output signal drives the sounder 1. The control loop from the Blocks 2, 3, 4, 5, 6, 7.1 to 7.N., 8 and 1 are now closed. How nice mentioned, as a result of the effect of this control loop, those by the incident The forces acting on the membrane are neutralized.

The digital filter 10, at the parallel inputs A, B, C and D the 4-bit word of the parallel outputs of the counter 5 is at the same clock frequency (3.072 MHz) clocked like the counter 5. The filter 10 serializes the parallel 4-word, due to the 64-fold oversampling, a 20-bit signal 12 with the 48 kHz sampling frequency at the output of the digital filter. 10 occurs. As digital filter 10, an FIR filter is preferably provided. With the digital Filtering also the noise components located above the listening area in the 4-bit output signal of counter 5 effectively suppressed.

It is understood that the 20-bit serial digital output signal 12 can also be in any other data formats can be converted. For this purpose, a format converter is shown in FIG. 1 11 indicated, the serial input SER.IN fed the signal 12 becomes. The clock input CLK and another, which serves the word synchronization FRM CTL input are connected to the clock 9. The optional one Format converter 11 produces a parallel output signal on its Multiple outputs, the first of which has LSB (corresponding to the least significant Bit) and the last with MSB (corresponding to the most significant bit) are designated. Furthermore, the format converter 11 has an output AES / EBU for an AES / EBU interface and a free OTHER output FORM for a selectable other digital format.

The control loop can be modified from the embodiment according to FIG. 1 as a 1-bit converter be carried out so that the output 5 when the counter 5 is omitted of the comparator 4 directly with the chain of differential and integration stages 7.1 to 7.N is connected. Furthermore, the modulated RF oscillation does not need to be demodulated first and then digitized (using an RF demodulator 3 with a downstream comparator 4), but can; like Figures 2 and 3 show, immediately converted in a stage 30 into a (digital) 1-bit signal become. The stage 30 contains a limiter amplifier or comparator 31 which the phase-modulated RF oscillation at the oscillating circuit coil 22 directly into one Rectangular signal converted with digital logic level. Another component is the phase-locked RF clock oscillator 33, which is the resonant circuit consisting of the capacitive sound receiver 2 and the oscillating circuit coil 22, via the coupling capacitor 35 excites and is synchronized by the clock oscillator 9 if necessary. Through a digital phase comparison between the digitized HF oscillation and the RF clock oscillator 33 immediately generates the 1-bit signal sequence, which the Information of the sound receptor deflection from the rest position carries. By doing considered embodiment according to FIGS. 2 and 3 this function is represented by a D flip-flop executed. The 1-bit signal is now with the required Oversampling, from which the desired quantization of the useful signal results, read into the digital filter 10 and the differential and integration stages 7.1 to 7.N fed.

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 eliminated and by one high-resolution analog-digital converter 50 (in the example considered as a counter trained) and a high-resolution digital-to-analog converter 60 are replaced, so that the control loop is closed again. In this case, is created immediately on Output of the analog-digital converter 50, the digital output signal 12, which in the considered example is shown as a serial signal and which in the previous described in the format converter 11 in any other formatted digital Output signals can be converted.

4 is the "waste product" of the digital microphone according to FIG. 1, so to speak to 3 shows an improved analog microphone, in which compared to the 1 only the sound receiver-sound generator combination 1/2, the RF demodulator 3 and the driver amplifier 8 were retained. The demodulated RF signal (with very small amplitude) at the output of the RF demodulator 3 is only amplified by means of an amplifier 20 in order to analog microphone output signal 23 to form high quality. From the output signal 23 is also in the amplifier 8, the driver signal for driving the sound generator 1 won. If desired, the analog output microphone output signal 23 in a conventional analog-to-digital converter 21 Digital signal can be converted, which in the example shown as serial signal is shown. The one converted to an analog microphone 4 remain from the advantages of the "real" digital microphone Microphones according to Figures 1 to 3, the advantages with regard to the low sound receptor deflection and the associated improvements explained at the beginning in terms of linear and non-linear distortions and sensitivity obtained if the amplifier 20 with a sufficiently large gain is trained. For example, with a gain factor of 100 Amplifier 20, the membrane deflection of the sound receiver 2 and that electrical output signal of the sound receiver 2 by the appropriate amount reduced.

Claims (36)

1. Process for converting an acoustic signal acting on a sound receptor of a sound receiver (2) to an electrical signal, characterized in that, upon action of the acoustic signal, a counter-signal is applied to the sound receptor in such a way that the sound receptor is maintained substantially in its neutral position despite action of the acoustic signal, the counter-signal is derived from a controlled variable of a closed-loop control circuit (1, 2, 3, 4, 5, 6, 7.1 to 7.N, 8) which comprises the sound receiver (2) as a component, and the controlled variable containing information on the acting acoustic signal, and each deviation of the receptor from its neutral position directly generates the digital information "zero" or "one".
2. Process according to Claim 1, characterized in that the counter-signal is generated by a sound source (1) which is acoustically coupled to the sound receiver (2).
3. Process according to Claim 1, characterized in that the counter-signal is generated by a sound source (1) and the sound receptor is provided as a component of a sound source / sound receiver combination which both receives and emits sound.
4. Process according to any one of Claims 1 to 3, characterized in that a diaphragm is provided as a sound receptor.
5. Process according to any one of Claims 1 to 3, characterized in that a spring-mounted component or component fashioned as a spring is provided as a sound receptor.
6. Process according to any one of Claims 1 to 5, characterized in that the sound source (1) and the sound receiver (2) are constructed according to any electroacoustic converter principles.
7. Process according to Claim 1, characterized in that deflections of the sound receptor are converted directly to a digital signal by means of a comparator (31).
8. Process according to Claim 7, characterized in that the digital signal is converted back to an analog signal by means of a digital-analog converter (6') for the purpose of obtaining the counter-signal.
9. Process according to any one of Claims 1 to 8, characterized in that the closed-loop control circuit operates according to the principle of a single-stage or multi-stage delta-sigma modulator, the receptor being included in the comparator function of the delta-sigma modulator.
10. Process according to Claim 9, characterized in that the delta-sigma modulator is of a single-bit or multi-bit type.
11. Process according to any one of Claims 1 to 10, characterized in that the sound receptor modulates the phase and/or amplitude of a HF resonant circuit, the capacitive component of which is the sound receiver (2).
12. Process according to Claim 11, characterized in that the HF resonant circuit is connected to a HF demodulator (3) which demodulates the phase-modulated and/or amplitude-modulated HF oscillation.
13. Process according to Claim 11, characterized in that the phase-modulated HF oscillation is directly digitized by a limiter comparator (31) and the digitized HF oscillation is converted directly by a digital phase comparator (32) to a digital signal carrying the receptor information.
14. Process according to Claim 1, characterized in that the deflections of the sound receptor are converted to an electrical analog signal which, following amplification (20), is applied to the sound source (1) as a counter-signal (Fig. 4).
15. Process according to Claim 14, characterized in that the analog electrical output signal is converted (21) to a digital signal.
16. Process according to any one of Claims 7 to 13, characterized in that the digital signal is filtered (10) in such a way that the time information is transformed into amplitude information.
17. Process according to Claim 16, characterized in that the transformed digital signal is converted to another data format, information being transformed from the time plane into the amplitude plane.
18. Process according to either of Claims 16 or 17, characterized in that a FIR filter is used as a digital filter (10).
19. Sound receiving arrangement, with a sound receiver (2) in which a sound receptor is provided, characterized in that, upon action of an acoustic signal, a counter-signal is applied to the sound receptor in such a way that the sound receptor is maintained substantially in its neutral position despite action of the acoustic signal, the counter-signal is derived from a controlled variable of a closed-loop control circuit (1, 2, 3, 4, 5, 6, 7.1 to 7.N, 8) which comprises the sound receiver (2) as a component, and the controlled variable containing information on the acting acoustic signal, and each deviation of the receptor from its neutral position directly generates the digital information "zero" or "one".
20. Sound receiving arrangement according to Claim 19, characterized in that the counter-signal is generated by a sound source (1) which is acoustically coupled to the sound receiver (2).
21. Sound receiving arrangement according to Claim 19, characterized in that the counter-signal is generated by a sound source (1) and the sound receptor is provided as a component of a sound source / sound receiver combination which both receives and emits sound.
22. Sound receiving arrangement according to any one of Claims 19 to 21, characterized in that a diaphragm is provided as a sound receptor.
23. Sound receiving arrangement according to any one of Claims 19 to 21, characterized in that a spring-mounted component or component fashioned as a spring is provided as a sound receptor.
24. Sound receiving arrangement according to any one of Claims 19 to 23, characterized in that the sound source (1) and the sound receiver (2) are constructed according to any electroacoustic converter principles.
25. Sound receiving arrangement according to Claim 19, characterized in that deflections of the sound receptor are converted directly to a digital signal by means of a comparator (31).
26. Sound receiving arrangement according to Claim 25, characterized in that the digital signal is converted back to an analog signal by means of a digital-analog converter (6') for the purpose of obtaining the counter-signal.
27. Sound receiving arrangement according to any one of Claims 1 to 26, characterized in that the closed-loop control circuit operates according to the principle of a single-stage or multi-stage delta-sigma modulator, the receptor being included in the comparator function of the delta-sigma modulator.
28. Sound receiving arrangernent according to Claim 27, characterized in that the delta-sigma modulator is of a single-bit or multi-bit type.
29. Sound receiving arrangement according to any one of Claims 19 to 28, characterized in that the sound receptor modulates the phase and/or amplitude of a HF resonant circuit, the capacitive component of which is the sound receiver (2).
30. Sound receiving arrangement according to Claim 29, characterized in that the HF resonant circuit is connected to a HF demodulator (3) which demodulates the phase-modulated and/or amplitude-modulated HF oscillation.
31. Sound receiving arrangement according to Claim 29, characterized in that the phase-modulated HF oscillation is directly digitized by a limiter comparator (31) and the digitized HF oscillation is converted directly by a digital phase comparator (32) to a digital signal carrying the receptor information.
32. Sound receiving arrangement according to Claim 19, characterized in that the deflections of the sound receptor are converted to an electrical analog signal which, following amplification (20), is applied to the sound source (1) as a counter-signal (Fig. 4).
33. Sound receiving arrangement according to Claim 32, characterized in that the analog electrical output signal is converted (21) to a digital signal.
34. Sound receiving arrangement according to any one of Claims 25 to 31, characterized by a digital filter (10) for filtering the digital signal in such a way that the time information is transformed into amplitude information.
35. Sound receiving arrangement according to Claim 34, characterized in that the transformed digital signal is converted to another data format, information being transformed from the time plane into the amplitude plane.
36. Sound receiving arrangement according to either of Claims 34 or 35, characterized in that a FIR filter is used as a digital filter (10).

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