A filter circuit applied to speech audio processing

Abstract

The utility model discloses a filter circuit applied to voice audio processing, including microphone, primary amplification high pass filter circuit, secondary amplification low pass filter circuit and automatic gain control circuit, the microphone is electrically connected with primary amplification high pass filter circuit, and secondary amplification low pass filter circuit is electrically connected with primary amplification high pass filter circuit and automatic gain control circuit, the microphone is used to convert the vibration of sound into weak electric signal. The utility model discloses a circuit structure that high gain preamplification and band pass filter cooperation are adopted, and automatic gain control is introduced, effectively realizes the remarkable restraint circuit inherent noise and environmental interference noise from source, simultaneously automatically adapts the big dynamic change of input signal, finally exports a high signal -to -noise ratio, no clipping distortion and amplitude stable high -quality voice signal, greatly promotes the overall effect of voice audio processing.

Description

Technical Field

[0001] This utility model relates to the field of filtering circuit technology, and in particular to a filtering circuit applied to voice audio processing. Background Technology

[0002] Voice and audio processing technology plays a core role in modern communication, speech recognition, audio recording and various intelligent interactive devices. Its primary task is to clearly and accurately pick up and enhance the target speech signal from a complex acoustic environment. In this process, the performance of the analog front-end processing circuit, especially the filtering circuit, directly determines the upper limit of the signal quality of the subsequent digital processing system. In the existing analog front-end design of voice acquisition, circuits with amplification and filtering functions are usually used to condition the signal output of the microphone.

[0003] However, the operational amplifiers and resistors in the filtering circuit automatically generate voltage noise and current noise during operation. These noises are superimposed on the weak speech signal, reducing the signal-to-noise ratio and thus affecting the processing effect of speech audio. In view of the above, this application proposes a filtering circuit for speech audio processing. Utility Model Content

[0004] The purpose of this invention is to address the shortcomings of existing technologies by proposing a filtering circuit for speech audio processing.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A filtering circuit for speech audio processing includes a microphone, a first-stage amplification high-pass filter circuit, a second-stage amplification low-pass filter circuit, and an automatic gain control circuit. The microphone is electrically connected to the first-stage amplification high-pass filter circuit, and the second-stage amplification low-pass filter circuit is electrically connected to the first-stage amplification high-pass filter circuit and the automatic gain control circuit.

[0007] The microphone is used to convert sound vibrations into weak electrical signals.

[0008] The first-stage amplification high-pass filter circuit is used to amplify the weak signal output by the microphone with high gain.

[0009] The two-stage amplified low-pass filter circuit is used to filter out high-frequency noise above the speech frequency range;

[0010] The automatic gain control circuit is used to detect the amplitude of the output signal in real time and compare it with an internally set reference level.

[0011] Preferably, the first-stage amplification high-pass filter circuit includes a resistor R1. One end of the resistor R1 is electrically connected to pin 2 of the microphone. The other end of the resistor R1 is electrically connected to one end of the capacitor C1 and one end of the resistor R2. The other end of the capacitor C1 is electrically connected to pin 1 of the operational amplifier OP1. Pins 2 and 3 of the operational amplifier OP1 are electrically connected to one end of the resistor R3 and one end of the capacitor C2, respectively. The other end of the resistor R2 is electrically connected to pin 4 of the operational amplifier OP1. Pin 4 of the operational amplifier OP1 is electrically connected to one end of the resistor R5.

[0012] Preferably, the secondary amplification low-pass filter circuit includes an operational amplifier OP2. Pin 1 of the operational amplifier OP2 is electrically connected to the other end of the resistor R5. Pin 2 of the operational amplifier OP2 is electrically connected to one end of the resistor R4 and one end of the capacitor C3. The other end of the capacitor C3 and pin 3 of the operational amplifier OP2 are both grounded. The other end of the resistor R4 is electrically connected to the other end of the resistor R3 and the other end of the capacitor C2.

[0013] Preferably, the automatic gain control circuit includes an operational amplifier OP3. Pin 1 of operational amplifier OP3 is electrically connected to one end of resistor R6 and one end of resistor R7. The other end of resistor R7 is grounded. The other end of resistor R6 is electrically connected to pin 1 of operational amplifier OP2. Pin 3 of operational amplifier OP3 is electrically connected to one end of resistor R8. Pin 5 of operational amplifier OP3 is electrically connected to one end of resistor R9. The other end of resistor R9 is electrically connected to pin 1 of operational amplifier OP2. One end of resistor R9 is electrically connected to… One end of capacitor C4 is connected to ground. The other end of capacitor C4 and the other end of resistor R8 are both grounded. Pin 4 of operational amplifier OP3 is electrically connected to one end of capacitor C5 and one end of resistor R10. The other end of capacitor C5 is electrically connected to pin 2 of error integrator IC. Pin 3 of error integrator IC is electrically connected to one end of resistor R11. The other ends of resistor R10 and resistor R11 are both grounded. Pin 1 of error integrator IC is electrically connected to one end of capacitor C6. The other end of capacitor C6 is electrically connected to one end of resistor R12.

[0014] Preferably, the high-pass cutoff frequency of the first-stage amplification high-pass filter circuit is set between 6kHz and 10kHz, and the low-pass cutoff frequency of the second-stage amplification low-pass filter circuit is set between 80Hz and 150Hz, together forming a bandpass filter suitable for the human speech frequency range.

[0015] Preferably, the operational amplifiers OP1 and OP2 are packaged in an external dual operational amplifier integrated circuit chip.

[0016] Preferably, all electronic components of the microphone, the first-stage amplification high-pass filter circuit, the second-stage amplification low-pass filter circuit, and the automatic gain control circuit are integrated on a single printed circuit board.

[0017] Compared with existing technologies, the beneficial effects of this utility model are:

[0018] 1. By adopting the "pre-amplification high gain" strategy, the weak microphone signal is immediately amplified at the very beginning of the signal chain, making its amplitude much greater than the noise introduced by subsequent filtering and the circuit itself. This design suppresses the influence of noise from the source, which can significantly improve the signal-to-noise ratio of the entire system and output a purer voice signal.

[0019] 2. By combining a first-stage amplification high-pass filter circuit and a second-stage amplification low-pass filter circuit, a bandpass filter with clear boundaries is formed, which can effectively filter out low-frequency vibration noise, wind noise, high-frequency hissing and radio frequency interference with concentrated energy, making the speech component in the output signal more prominent and greatly improving the clarity of speech. In addition, with the built-in automatic gain control circuit, it can adaptively process input signals of different intensities.

[0020] This invention employs a circuit structure that combines high-gain preamplifier and bandpass filter with automatic gain control. This effectively suppresses inherent circuit noise and environmental interference noise at the source, while automatically adapting to large dynamic changes in the input signal. Ultimately, it outputs a high-signal-to-noise ratio, clipping-free, and amplitude-stable high-quality voice signal, greatly improving the overall effect of voice audio processing. Attached Figure Description

[0021] Figure 1 This is a block diagram of a filtering circuit for speech audio processing proposed in this utility model;

[0022] Figure 2 This utility model provides a circuit diagram showing the connection between a microphone, a first-stage high-pass amplification filter circuit, and a second-stage low-pass amplification filter circuit in a filtering circuit used for speech audio processing.

[0023] Figure 3 This invention provides a circuit diagram of an automatic gain control circuit for use in a filtering circuit for voice audio processing. Detailed Implementation

[0024] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present utility model. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments.

[0025] Reference Figure 1-3A filtering circuit for voice audio processing includes a microphone, a first-stage amplification high-pass filter circuit, a second-stage amplification low-pass filter circuit, and an automatic gain control circuit. The microphone is electrically connected to the first-stage amplification high-pass filter circuit, and the second-stage amplification low-pass filter circuit is electrically connected to the first-stage amplification high-pass filter circuit and the automatic gain control circuit. All electronic components of the microphone, the first-stage amplification high-pass filter circuit, the second-stage amplification low-pass filter circuit, and the automatic gain control circuit are integrated on a single printed circuit board.

[0026] A microphone is used to convert sound vibrations into weak electrical signals; the microphone used is an analog electret condenser microphone.

[0027] The first-stage high-pass filter circuit is used to amplify the weak signal output by the microphone with high gain. The first-stage high-pass filter circuit includes a resistor R1, one end of which is electrically connected to pin 2 of the microphone. The other end of the resistor R1 is electrically connected to one end of a capacitor C1 and one end of a resistor R2. The other end of the capacitor C1 is electrically connected to pin 1 of the operational amplifier OP1. Pins 2 and 3 of the operational amplifier OP1 are electrically connected to one end of a resistor R3 and one end of a capacitor C2, respectively. The other end of the resistor R2 is electrically connected to pin 4 of the operational amplifier OP1. Pin 4 of the operational amplifier OP1 is electrically connected to one end of a resistor R5.

[0028] Among them, resistor R1 is a pull-up resistor, and resistor R2, capacitor C2 and resistor R3 form a feedback network;

[0029] The operation of the first-stage high-pass filter circuit is as follows: the AC signal output from the microphone is blocked by capacitor C1 and then sent to the non-inverting input of operational amplifier OP1. At the same time, the feedback network composed of resistor R2, capacitor C2 and resistor R3 works together to form a high gain amplification of 1+(R2 / R3) times for the high-frequency voice signal, while the low-frequency noise is suppressed by the capacitive reactance attenuation of capacitors C1 and C2. Finally, the mid-to-high frequency signal that has been initially amplified and purified is sent out from the output of operational amplifier OP1 through isolation resistor R5.

[0030] The two-stage amplification low-pass filter circuit is used to filter out high-frequency noise above the speech frequency range. The two-stage amplification low-pass filter circuit includes an operational amplifier OP2. Pin 1 of the operational amplifier OP2 is electrically connected to the other end of the resistor R5. Pin 2 of the operational amplifier OP2 is electrically connected to one end of the resistor R4 and one end of the capacitor C3. The other end of the capacitor C3 and pin 3 of the operational amplifier OP2 are both grounded. The other end of the resistor R4 is electrically connected to the other end of the resistor R3 and the other end of the capacitor C2.

[0031] The operation of the two-stage amplification low-pass filter circuit is as follows: the signal from resistor R5 is connected to the inverting input of operational amplifier OP2. Its feedback network consists of resistor R4 and capacitor C3. When the low-frequency voice signal passes through, capacitor C3 exhibits high capacitive reactance, and the circuit amplifies normally at a certain gain. However, when high-frequency noise components appear, the capacitive reactance of C3 decreases, forming a negative feedback path, which diverts the high-frequency signal components to ground, thereby filtering out high-frequency noise while retaining and amplifying the effective voice band.

[0032] The high-pass cutoff frequency of the first-stage amplification high-pass filter circuit is set between 6kHz and 10kHz, and the low-pass cutoff frequency of the second-stage amplification low-pass filter circuit is set between 80Hz and 150Hz. Together, they form a bandpass filter suitable for the human speech frequency range. Operational amplifiers OP1 and OP2 are packaged in an external dual operational amplifier integrated circuit chip.

[0033] The automatic gain control (AGC) circuit is used to detect the amplitude of the output signal in real time and compare it with an internally set reference level. The AGC circuit includes operational amplifier OP3. Pin 1 of operational amplifier OP3 is electrically connected to one end of resistor R6 and one end of resistor R7. The other end of resistor R7 is grounded. The other end of resistor R6 is electrically connected to pin 1 of operational amplifier OP2. Pin 3 of operational amplifier OP3 is electrically connected to one end of resistor R8. Pin 5 of operational amplifier OP3 is electrically connected to one end of resistor R9. The other end of resistor R9 is connected to pin 1 of operational amplifier OP2. 1. Electrical connection: One end of resistor R9 is electrically connected to one end of capacitor C4. The other end of capacitor C4 and the other end of resistor R8 are both grounded. Pin 4 of operational amplifier OP3 is electrically connected to one end of capacitor C5 and one end of resistor R10. The other end of capacitor C5 is electrically connected to pin 2 of error integrator IC. Pin 3 of error integrator IC is electrically connected to one end of resistor R11. The other ends of resistor R10 and the other end of resistor R11 are both grounded. Pin 1 of error integrator IC is electrically connected to one end of capacitor C6. The other end of capacitor C6 is electrically connected to one end of resistor R12.

[0034] The resistors R7 and R8 and the capacitor C4 form a precision full-wave rectifier circuit, which converts the AC amplitude of the output signal into DC voltage.

[0035] This invention employs a circuit structure that combines high-gain preamplifier and bandpass filter with automatic gain control. This effectively suppresses inherent circuit noise and environmental interference noise at the source, while automatically adapting to large dynamic changes in the input signal. Ultimately, it outputs a high-signal-to-noise ratio, clipping-free, and amplitude-stable high-quality voice signal, greatly improving the overall effect of voice audio processing.

[0036] Working principle: When in use, the microphone converts the sound signal into a weak electrical signal. This signal first enters the first-stage amplification high-pass filter circuit composed of operational amplifier OP1 through coupling capacitor C1. At the same time, the high-pass network composed of capacitor C1 and resistor R2 in series is responsible for blocking low-frequency noise below 80Hz. Meanwhile, operational amplifier OP1 works together with resistors R2 and R3 to amplify the effective frequency band signal, achieving initial signal amplitude enhancement and initial low-frequency noise filtering. The amplified signal is transmitted through resistor R5 to the second-stage amplification low-pass filter circuit composed of operational amplifier OP2, resistor R4, and capacitor C3. Through multi-stage RC filtering, high-frequency components above 6kHz are precisely attenuated, completing further shaping of the speech frequency band.

[0037] The signal, after two stages of filtering and amplification, then enters the automatic gain control (AGC) stage. On one hand, it is fed to the output buffer stage composed of operational amplifier OP3 via resistor R6. On the other hand, the signal amplitude information is converted into a DC voltage by a precision rectifier and detector circuit composed of resistors R8 and R9 and capacitor C4. This DC voltage, along with the reference voltage Vref set by resistor R11, is fed into the error integrator IC for comparison and amplification. The error integrator IC, through the integration action of capacitor C6 and resistor R12 in its feedback network, generates a smooth control voltage Vc by integrating with a specific time constant. When the output signal is too strong, the control... The control voltage Vc decreases, thereby reducing the overall gain. When the output signal is too weak, the control voltage Vc increases, thereby increasing the overall gain. This achieves dynamic stability of the output amplitude, ensuring that the subsequent ADC acquires a voice signal with constant amplitude and optimal signal-to-noise ratio. By adopting a circuit structure that combines high-gain preamplifier and bandpass filter with automatic gain control, the inherent noise of the circuit and environmental interference noise are significantly suppressed from the source. At the same time, it automatically adapts to large dynamic changes in the input signal, and finally outputs a high-quality voice signal with high signal-to-noise ratio, no clipping distortion, and stable amplitude, which greatly improves the overall effect of voice audio processing.

[0038] The above description is only a preferred embodiment of the present utility model, but the protection scope of the present utility model is not limited thereto. Any equivalent substitutions or changes made by those skilled in the art within the technical scope disclosed in the present utility model, based on the technical solution and the inventive concept of the present utility model, should be included within the protection scope of the present utility model.

Claims

1. A filtering circuit for speech audio processing, characterized in that, It includes a microphone, a first-stage amplification high-pass filter circuit, a second-stage amplification low-pass filter circuit, and an automatic gain control circuit. The microphone is electrically connected to the first-stage amplification high-pass filter circuit, and the second-stage amplification low-pass filter circuit is electrically connected to the first-stage amplification high-pass filter circuit and the automatic gain control circuit. The microphone is used to convert sound vibrations into weak electrical signals. The first-stage amplification high-pass filter circuit is used to amplify the weak signal output by the microphone with high gain. The two-stage amplified low-pass filter circuit is used to filter out high-frequency noise above the speech frequency range; The automatic gain control circuit is used to detect the amplitude of the output signal in real time and compare it with an internally set reference level.

2. The filtering circuit for speech audio processing according to claim 1, characterized in that, The first-stage amplification high-pass filter circuit includes a resistor R1. One end of the resistor R1 is electrically connected to pin 2 of the microphone. The other end of the resistor R1 is electrically connected to one end of the capacitor C1 and one end of the resistor R2. The other end of the capacitor C1 is electrically connected to pin 1 of the operational amplifier OP1. Pins 2 and 3 of the operational amplifier OP1 are electrically connected to one end of the resistor R3 and one end of the capacitor C2, respectively. The other end of the resistor R2 is electrically connected to pin 4 of the operational amplifier OP1. Pin 4 of the operational amplifier OP1 is electrically connected to one end of the resistor R5.

3. A filtering circuit for speech audio processing according to claim 2, characterized in that, The two-stage amplification low-pass filter circuit includes an operational amplifier OP2. Pin 1 of the operational amplifier OP2 is electrically connected to the other end of resistor R5. Pin 2 of the operational amplifier OP2 is electrically connected to one end of resistor R4 and one end of capacitor C3. The other end of capacitor C3 and pin 3 of the operational amplifier OP2 are both grounded. The other end of resistor R4 is electrically connected to the other end of resistor R3 and the other end of capacitor C2.

4. A filtering circuit for speech audio processing according to claim 3, characterized in that, The automatic gain control circuit includes an operational amplifier OP3. Pin 1 of operational amplifier OP3 is electrically connected to one end of resistor R6 and one end of resistor R7. The other end of resistor R7 is grounded. The other end of resistor R6 is electrically connected to pin 1 of operational amplifier OP2. Pin 3 of operational amplifier OP3 is electrically connected to one end of resistor R8. Pin 5 of operational amplifier OP3 is electrically connected to one end of resistor R9. The other end of resistor R9 is electrically connected to pin 1 of operational amplifier OP2. One end of resistor R9 is electrically connected to one end of capacitor C4. The other end of capacitor C4 and the other end of resistor R8 are both grounded. Pin 4 of operational amplifier OP3 is electrically connected to one end of capacitor C5 and one end of resistor R10. The other end of capacitor C5 is electrically connected to pin 2 of error integrator IC. Pin 3 of error integrator IC is electrically connected to one end of resistor R11. The other ends of resistor R10 and the other end of resistor R11 are both grounded. Pin 1 of error integrator IC is electrically connected to one end of capacitor C6. The other end of capacitor C6 is electrically connected to one end of resistor R12.

5. A filtering circuit for speech audio processing according to claim 1, characterized in that, The high-pass cutoff frequency of the first-stage amplification high-pass filter circuit is set between 6kHz and 10kHz, and the low-pass cutoff frequency of the second-stage amplification low-pass filter circuit is set between 80Hz and 150Hz, together forming a bandpass filter suitable for the human speech frequency range.

6. A filtering circuit for speech audio processing according to claim 4, characterized in that, The operational amplifiers OP1 and OP2 are packaged in an external dual operational amplifier integrated circuit chip.

7. A filtering circuit for speech audio processing according to claim 1, characterized in that, All electronic components of the microphone, the first-stage high-pass filter circuit, the second-stage low-pass filter circuit, and the automatic gain control circuit are integrated on a single printed circuit board.

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