Audio signal generating device and method

Abstract

The invention discloses an audio signal generation device and method, relates to the technical field of acoustic measurement, and solves the problems of single function, low output amplitude frequency, low signal quality and high cost of an audio signal generator in the prior art. According to the method, a main control unit, an audio data playing unit, a multi-stage low-pass filter unit and a program control precision attenuator unit are included, a digital signal processing technology is adopted, a hardware circuit is simplified, the hardware cost can be reduced, multiple audio signal generation functions are included, the performance is excellent, and the method can be suitable for multiple scenes. The tail-stage amplification circuit adopts a filter design thought, supports output of high-frequency sinusoidal signals and reduces high-frequency noise in the circuit at the same time, so that the total distortion of the output signals is as low as 0.01% or below within the frequency range of 10-40 kHz, the highest output frequency is increased to 1 MHz, the lowest output frequency reaches 0.05 Hz, and the verification requirements of octave and fractional octave filters are met.

Description

Technical Field

[0001] The present application relates to the field of acoustic measurement technology, and in particular to an audio signal generating device and method. Background Art

[0002] Audio signal generator is a portable signal generating device, which is mainly used for hall sound testing and noise monitoring system verification. It is developed with digital signal processing technology and modular design. It has the advantages of multi-function, high performance, small size, low power consumption and easy operation.

[0003] Currently, there are relatively few portable audio signal generators on the market that have high precision, low distortion, precise attenuation, high-quality small signal generation, and low background noise. Audio signal generators that meet both low distortion and small signal output are often expensive and bulky, making them inconvenient to carry. Therefore, a portable, multifunctional, high-precision, low-distortion, high-quality small signal generation, long working time, and stable performance audio signal generator is the development trend.

[0004] For example, the audio signal generator model YCR-SG030 only supports a maximum output signal frequency of 20kHz, and supports only a few types of output signals, which cannot meet the sound level meter calibration requirements. Another example is the B&K3161 audio signal generator, which only supports an output frequency of 204kHz, which cannot meet the sound level meter filter calibration requirements, and is expensive. There are almost no similar competing products in the domestic market. As an important component of acoustic instruments, it is particularly important to have a multifunctional audio signal generator that can meet various calibration requirements.

[0005] The existing audio signal generator technology has the following main disadvantages:

[0006] 1. In the JJG 676-2019 vibration meter calibration procedure, the frequency range requirements for the comparative vibration standard device and the absolute vibration standard device are both as low as 0.1 Hz, while the audio signal generator in the prior art is difficult to reach an output frequency of 0.1 Hz.

[0007] 2. In the calibration of acoustic and vibration measuring instruments, it is necessary to meet the requirements of JJG 449-2014 Octave and Fractional Octave Filters and JJF 1555-2015 Octave and 1 / 3 Octave Filter Type Evaluation Outline. Both documents put forward requirements for signal generators. In particular, JJF 1555-2015 clearly states that the total distortion of the output signal of the signal generator should not be greater than 0.01% for the test of the first-level filter within the frequency range of 10Hz~40kHz. It is difficult for audio signal generators on the market to meet this requirement.

[0008] 3. According to JJG 449-2014 Octave and Fractional Octave Filters and JJF 1555-2015 Octave and 1 / 3 Octave Filter Type Evaluation Outline, one of the relative attenuation measurement requirements is that if the octave and 1 / 3 octave filters cover 80kHz, the output frequency of the audio signal generator needs to reach 999997.9857Hz. It is difficult for audio signal generators on the market to meet this requirement.

[0009] 4. The audio signal generator in the prior art has a single function and mostly uses hardware circuits to generate signals. The signal types only support a few waveform outputs such as sine waves and swept sine waves. When used as a signal source for acoustic devices that require complex signal outputs, it is often necessary to carry several instruments.

[0010] 5. The signal quality of the audio signal generator in the prior art is difficult to meet the requirements. As the signal source of the device in the acoustic field, it has strict requirements on parameters such as total distortion, attenuation accuracy, small signal accuracy, and background noise. In the application scenario where the sound level meter range is expanded, the low-frequency and low-voltage signal output can no longer meet the calibration requirements. Summary of the invention

[0011] The purpose of the present application is to overcome the problems of the prior art such as single function of audio signal generator, low output amplitude frequency, low signal quality and high cost, and to provide an audio signal generating device and method.

[0012] In a first aspect, an audio signal generating device is provided, comprising a main control unit, wherein the main control unit is electrically connected to an audio data playback unit, wherein the audio data playback unit is electrically connected to a multi-stage low-pass filter unit, wherein the multi-stage low-pass filter unit is electrically connected to a programmable precision attenuator unit, wherein an output end of the programmable precision attenuator unit is electrically connected to a BNC interface, wherein both the multi-stage low-pass filter unit and the programmable precision attenuator unit are control-connected to the main control unit, wherein the main control unit is used to calculate and generate a specified AC signal and output a signal through the audio data playback unit, and wherein the main control unit is further used to control the multi-stage low-pass filter unit to select a low-pass filter of a corresponding frequency according to the frequency of the output signal and to control the attenuation amplitude of the signal by the programmable precision attenuator unit.

[0013] In some possible implementations, a power management unit is also included, the power management unit includes an isolated AC transformer circuit for connecting to the mains, the isolated AC transformer circuit is electrically connected to a rectifier and filter circuit, the rectifier and filter circuit is electrically connected to a rechargeable power supply and a linear voltage regulator circuit, the rechargeable power supply and the linear voltage regulator circuit are electrically connected to the main control unit, the audio data playback unit, the multi-stage low-pass filter unit and the programmable precision attenuator unit through a path selection module, wherein the path selection module is used to detect whether the isolated AC transformer circuit is connected to the mains, if not connected to the mains, it is powered by the rechargeable power supply, if connected to the mains, it is powered by the linear voltage regulator circuit.

[0014] In some possible implementations, the path selection module includes a power detection module, a control module and a first relay, wherein the power detection module is used to detect whether the isolated AC transformer circuit is connected to the mains and send the detection result to the control module, and the control module is used to control the first relay to select a rechargeable power supply or a linear voltage regulator circuit for power supply according to the detection result.

[0015] In some possible implementations, the main control unit, audio signal playback unit, multi-stage low-pass filter unit, programmable precision attenuator unit and power management unit are all arranged in a shell, the shell is embedded with an external power interface for connecting to the mains, the input end of the isolated AC transformer circuit is electrically connected to the external power interface, and the BNC interface is arranged on the surface of the shell.

[0016] In some possible implementations, the main control unit is also electrically connected to a touch screen and a control panel, and the touch screen and the control panel are both arranged on the surface of the shell.

[0017] In some possible implementations, the main control unit is also electrically connected to a DB9 interface and an RJ45 interface, and the DB9 interface and the RJ45 interface are both arranged on the surface of the shell.

[0018] In some possible implementations, the audio data playback unit includes a precision digital-to-analog converter and a direct digital frequency synthesizer, the precision digital-to-analog converter and the direct digital frequency synthesizer are both electrically connected to a main control unit, the output end of the precision digital-to-analog converter is electrically connected to a first adding circuit, the output end of the direct digital frequency synthesizer is electrically connected to a second adding circuit, the first adding circuit and the second adding circuit are respectively electrically connected to two static contacts of a second relay, the moving contact of the second relay is electrically connected to a differential-to-single-ended circuit, the second relay is control-connected to the main control unit, and the differential-to-single-ended circuit is electrically connected to a multi-stage low-pass filter unit.

[0019] In some possible implementations, the programmable precision attenuator unit includes a sixth relay, a signal amplifier, a -10db attenuator, a precision operational amplifier and a π-type resistance attenuation network, the moving contact of the sixth relay is electrically connected to the output end of the low-pass filter unit, and the two static contacts of the sixth relay are electrically connected to the seventh relay and the -10db attenuator, respectively, wherein one of the static contacts of the sixth relay is electrically connected to the moving contact of the seventh relay, the two static contacts of the seventh relay are electrically connected to the signal amplifier and the single-ended electrical signal output bus, respectively, the output end of the signal amplifier is electrically connected to the single-ended electrical signal output bus, the output end of the -10db attenuator is electrically connected to the precision operational amplifier, the output end of the precision operational amplifier is electrically connected to the π-type resistance attenuation network, the π-type resistance attenuation network is electrically connected to the single-ended electrical signal output bus through a number of eighth relays, the single-ended electrical signal output bus is connected to a BNC interface and a single-ended to differential unit, and the sixth relay, the seventh relay and the eighth relay are all controlled and connected to the main control unit.

[0020] In a second aspect, a method for generating an audio signal is provided, including a method for controlling an audio signal generating device as described in any one of the implementations of the first aspect, the method comprising:

[0021] S100, obtaining a signal type and signal parameters set by a user, wherein the signal type includes a sine signal, white noise, narrowband white noise, pink noise, narrowband pink noise, a swept frequency sine wave, a swept amplitude sine wave and a burst tone, and the signal parameters include frequency, amplitude and attenuation;

[0022] S200, generating a specified signal according to the signal type and signal parameters, and outputting the signal to a multi-stage low-pass filter unit through an audio data playback unit;

[0023] S300, according to the frequency of the signal, select a low-pass filter of a corresponding frequency in the multi-stage low-pass filter unit to filter the signal, wherein, if the frequency of the signal is in the range of (200KHz-1MHz], select a 1MHz low-pass filter for filtering; if the frequency of the signal is in the range of (80KHz-200KHz], select a 1MHz low-pass filter and a 200KHz low-pass filter in sequence for filtering; if the frequency of the signal is in the range of (40KHz-80KHz], select a 1MHz low-pass filter, a 200KHz low-pass filter and an 80KHz low-pass filter in sequence for filtering; if the frequency of the signal is in the range of (0KHz-40KHz], select a 1MHz low-pass filter, a 200KHz low-pass filter, an 80KHz low-pass filter and a 40KHz low-pass filter in sequence for filtering;

[0024] S400, outputting the filtered signal to the program-controlled precision attenuation unit, using the program-controlled precision attenuation unit to amplify the filtered signal or attenuate it in a step unit of -10dB, and outputting the signal processed by the program-controlled precision attenuation unit through a BNC interface.

[0025] This application has the following beneficial effects:

[0026] 1. The audio signal generating device of the present application adopts digital signal processing technology, simplifies the hardware circuit, can reduce hardware costs, and includes multiple audio signal generating functions, has excellent performance, and can be applied to a variety of scenarios.

[0027] 2. The final-stage amplifier circuit of the audio signal generating device of the present application adopts a filter design concept, which supports the output of high-frequency (maximum 1MHz) sinusoidal signals while reducing the high-frequency noise in the circuit, so that the total distortion of the output signal is as low as less than 0.01% within the frequency range of 10Hz-40kHz.

[0028] 3. The output signal amplitude upper limit of the audio signal generating device of the present application is high, supporting a maximum of 20Vrms (Z-weighted) sinusoidal signal output, and the output signal amplitude lower limit is low, supporting a minimum of 10μVrms (Z-weighted) sinusoidal signal output.

[0029] 4. The audio signal generating device of the present application adopts a design shared by a precision digital-to-analog converter and a direct digital frequency synthesizer, which takes into account the output quality of both low-frequency analog signals and high-frequency analog signals to the greatest extent. The maximum output frequency is increased to 1MHz, and the minimum output frequency reaches 0.05Hz, which meets the requirements for octave and fractional octave filter calibration.

[0030] 5. The audio signal generating device of the present application utilizes the differential output characteristics of the precision digital-to-analog converter, and uses an addition circuit to further increase the maximum output value of the precision digital-to-analog converter, thereby improving the signal-to-noise ratio of the precision digital-to-analog converter output. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application.

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0033] Figure 1is a structural block diagram of an audio signal generating device according to Embodiment 1 of the present application;

[0034] Figure 2 is a structural block diagram of a power management unit in the audio signal generating device of Example 1 of the present application;

[0035] Figure 3 is a structural block diagram of an audio data playback unit in an audio signal generating device according to Embodiment 1 of the present application;

[0036] Figure 4 is a structural block diagram of a multi-stage low-pass filter unit in an audio signal generating device according to Embodiment 1 of the present application;

[0037] Figure 5 is a structural block diagram of a program-controlled precision attenuator unit in the audio signal generating device of Example 1 of the present application;

[0038] Figure 6 is a stereoscopic diagram of the audio signal generating device of Example 1 of the present application;

[0039] Figure 7 is a front view of the audio signal generating device of Example 1 of the present application;

[0040] Figure 8 is a rear view of the audio signal generating device of Example 1 of the present application;

[0041] Fig. 9 is a program hierarchy diagram of the main control unit in the audio signal generating device of Example 1 of the present application;

[0042] Fig.10 This is a flowchart of the audio signal generating method of Example 2 of the present application.

[0043] Reference numerals: 100, main control unit; 200, audio data playback unit; 201, precision digital-to-analog converter; 202, direct digital frequency synthesizer; 203, first addition circuit; 204, second addition circuit; 205, second relay; 206, differential to single-ended circuit; 300, multi-stage low-pass filter unit; 301, 1MHz low-pass filter; 302, 200KHz low-pass filter; 303, 80KHz low-pass filter; 304, 40KHz low-pass filter; 305, third relay; 306, fourth relay; 307, fifth relay; 400, programmable precision attenuator unit; 401, sixth relay; 402, signal amplifier; 40 3. -10db attenuator; 404. precision operational amplifier; 405. π-type resistor attenuation network; 406. seventh relay; 407. eighth relay; 409. single-ended electrical signal output bus; 500. BNC interface; 600. power management unit; 601. isolated AC transformer circuit; 602. rectifier filter circuit; 603. rechargeable power supply; 604. linear voltage regulator circuit; 605. channel selection module; 6051. power detection module; 6052. control module; 6053. first relay; 700. housing; 701. external power interface; 702. touch screen; 703. control panel; 704. DB9 interface; 705. RJ45 interface. DETAILED DESCRIPTION

[0044] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0045] Example 1

[0046] like Figure 1As shown, an audio signal generating device involved in Embodiment 1 of the present application includes a power management unit 600, a main control unit 100, an audio data playback unit 200, a multi-stage low-pass filter unit 300 and a programmable precision attenuator unit 400. Specifically, the main control unit 100 is electrically connected to the audio data playback unit 200, the audio data playback unit 200 is electrically connected to the multi-stage low-pass filter unit 300, the multi-stage low-pass filter unit 300 is electrically connected to the programmable precision attenuator unit 400, and the output end of the programmable precision attenuator unit 400 is electrically connected to the BNC interface 5 00, the multi-stage low-pass filter unit 300 and the programmable precision attenuator unit 400 are both controlled and connected to the main control unit 100, wherein the main control unit 100 is used to calculate and generate a specified AC signal and output the signal through the audio data playback unit 200. The main control unit 100 is also used to control the multi-stage low-pass filter unit 300 to select a low-pass filter of a corresponding frequency according to the output signal frequency and to control the attenuation amplitude of the signal by the programmable precision attenuator unit 400. The power management unit 600 is used to generate a system power supply to provide power for the entire device and has over-current and over-voltage protection functions.

[0047] like Figure 2As shown, the power management unit 600 includes an isolated AC transformer circuit 601 for connecting to the mains. The isolated AC transformer circuit 601 mainly uses an isolated AC transformer to convert the 220V mains into isolated AC power, and at the same time isolates the circuit interference caused by multiple devices being connected to the mains at the same time. The isolated AC transformer circuit 601 is electrically connected to a rectifier filter circuit 602. The rectifier filter circuit 602 is used to rectify the AC power to obtain a stable DC power supply. The rectifier filter circuit 602 is electrically connected to a rechargeable power supply 603 and a linear voltage regulator circuit 604. The rectifier filter circuit 602 can charge the rechargeable power supply 603, and can also power subsequent circuit modules through the linear voltage regulator circuit 604. The rechargeable power supply 603 has multiple functions such as overcharge protection, over-discharge protection and overcurrent protection, and can send information such as charging status and residual current to the main control unit 100. The display screen shows that the rechargeable power supply 603 can be a rechargeable lithium battery, a rechargeable nickel-cadmium battery, etc. The linear voltage regulator circuit 604 is used to perform voltage conversion and voltage regulation on the power supply output by the rectifier and filter circuit 602 to obtain a stable and low-noise DC voltage to power circuits such as the main control unit 100, the audio data playback unit 200, the multi-stage low-pass filter unit 300 and the programmable precision attenuator unit 400. The rechargeable power supply 603 and the linear voltage regulator circuit 604 are electrically connected to the main control unit 100, the audio data playback unit 200, the multi-stage low-pass filter unit 300 and the programmable precision attenuator unit 400 through the path selection module 605, wherein the path selection module 605 is used to detect whether the isolated AC transformer circuit 601 is connected to the mains. If not, the rechargeable power supply 603 is used to supply power. If connected to the mains, the linear voltage regulator circuit 604 is used to supply power.

[0048] Specifically, the path selection module 605 includes a power detection module 6051, a control module 6052 and a first relay 6053, wherein the power detection module 6051 is used to detect whether the isolated AC transformer circuit 601 is connected to the mains and send the detection result to the control module 6052, and the control module 6052 is used to control the first relay 6053 to select the rechargeable power supply 603 or the linear voltage regulator circuit 604 for power supply according to the detection result. When the 220V mains is not connected, the control module 6052 controls the first relay 6053 to disconnect the linear voltage regulator circuit 604, and the subsequent main control unit 100 and other circuits are powered by the rechargeable power supply 603; when the 220V mains is connected, the control module 6052 controls the first relay 6053 to disconnect the rechargeable power supply 603, and the subsequent main control unit 100 and other circuits are powered by the linear voltage regulator circuit 604. This ensures that the rechargeable power source 603 only works in the charging or discharging state, avoids the situation where the rechargeable power source 603 is used while being charged, improves the safety and service life of the rechargeable power source 603 when in use, and at the same time minimizes the impact of the electrical noise generated when the rechargeable power source 603 is charged on the background of subsequent circuits.

[0049] like Figure 6-Figure 8 As shown, it also includes a shell 700, a main control unit 100, an audio signal playback unit, a multi-stage low-pass filter unit 300, a programmable precision attenuator unit 400 and a power management unit 600 are all arranged in the shell 700, the shell 700 is embedded with an external power interface 701 for connecting to the mains, the input end of the isolation AC transformer circuit 601 is electrically connected to the external power interface 701, the BNC interface 500 is arranged on the surface of the shell 700, the main control unit 100 is also electrically connected to a touch screen 702 and a control panel 703, the touch screen 702 and the control panel 703 are both arranged on the surface of the shell 700, the main control unit 100 is also electrically connected to a DB9 interface 704 and an RJ45 interface 705, the DB9 interface 704 and the RJ45 interface 705 are both arranged on the surface of the shell 700, the DB9 interface 704 and the RJ45 interface 705 are respectively used for serial communication and network communication, and the host computer is connected through these two interfaces, so as to realize automatic control.

[0050] like Figure 7 FIG. 7 is a front view of the housing 700. In this embodiment, the control panel 703 includes the following 15 buttons:

[0051] (1) On / off button, used to turn on and off the audio signal generating device;

[0052] (2) Parameter ± key: used to adjust the parameter at the output signal cursor position;

[0053] (3) Cursor ± keys: adjust the cursor position;

[0054] (4) 10dB± key, 1dB± key, 0.1dB± key: adjust the amplitude of the output signal, the adjustment steps are 10dB, 1dB and 0.1dB respectively;

[0055] (5) Frequency key: It is a shortcut key. When the output signal is a sine signal, click this key, the cursor on the display interface jumps to the frequency, and a numeric keyboard is displayed, allowing the user to quickly set the frequency of the output signal.

[0056] (6) Save key: save the current output signal type and signal parameters;

[0057] (7) Exit key: After clicking this key, the cursor exits and the parameter ± is used to select the frequency of the output signal;

[0058] In addition, the touch screen 702 uses a 7-inch capacitive screen with a resolution of 1024*600. The instrument can be operated by both touch screen and physical buttons, which is convenient for users to use.

[0059] like Fig. 9 As shown in FIG. 1 , it is a program hierarchy diagram of the main control unit 100. The main functions of the main control unit 100 are as follows:

[0060] (1) Used to determine the type of signal that needs to be output, calculate and generate a specified AC signal, and output it through the audio data playback unit 200 to achieve signal generation;

[0061] (2) Determine the characteristics of the signal currently to be output, such as frequency and amplitude, and control the corresponding relay through the IO port of the main control unit 100 to select which group of filters to output the signal;

[0062] (3) Controlling the attenuation amplitude of the programmable precision attenuator unit 400 through the IO port of the main control unit 100;

[0063] (4) Control the display of the display screen, the buttons of the control panel 703, and project processing, etc.;

[0064] (5) Control other necessary auxiliary components.

[0065] It should be noted that the generated electrical signal can be set according to the needs of the user. The data of all signals are generated by the main control unit 100, and no additional signal generating circuit is required. The main control unit 100, the audio data playback unit 200, the multi-stage low-pass filter unit 300, and the programmable precision attenuator unit 400 constitute the signal generating system, and the rest are necessary auxiliary components.

[0066] The audio signal generating device of this embodiment has multiple signal generating functions such as sine signal, white noise, narrow-band white noise, pink noise, narrow-band pink noise, swept frequency sine wave, swept amplitude sine wave, burst tone, etc., and has excellent performance and can be applied to various occasions.

[0067] like Figure 3 As shown, the audio data playback unit 200 includes a precision digital-to-analog converter 201, a direct digital frequency synthesizer 202 and a differential-to-single-ended circuit 206. The precision digital-to-analog converter 201 and the direct digital frequency synthesizer 202 are both electrically connected to the main control unit 100. The precision digital-to-analog converter 201 uses a high-performance audio DAC chip. The main control unit 100 outputs the digital signal to the DAC chip through the I2S interface to generate a high-quality analog signal; the direct digital audio synthesizer uses a 14-bit DDS chip. The main control unit 100 sends the required frequency, amplitude, phase and other parameters through the SPI interface. Sent to the DDS chip to generate a high-speed analog signal; the output end of the precision digital-to-analog converter 201 is electrically connected to the first adding circuit 203, the output end of the direct digital frequency synthesizer 202 is electrically connected to the second adding circuit 204, the first adding circuit 203 and the second adding circuit 204 are electrically connected to the two static contacts of the second relay 205 respectively, the moving contact of the second relay 205 is electrically connected to the differential-to-single-ended circuit 206, the second relay 205 is controlled and connected to the main control unit 100, and the differential-to-single-ended circuit 206 is electrically connected to the multi-stage low-pass filter unit 300.

[0068] It should be noted that audio data playback refers to the process of using a DAC chip and a DDS chip to convert a digital signal output from the main control unit 100, after DAC conversion or DDS conversion, through a differential to single-ended short circuit and a low-pass filter to output the signal. Since the DAC chip and the DDS chip have a dual-channel output function, the main control unit 100 can control the two channels of the DAC chip or the DDS chip to output the same analog signal, and the first addition circuit 203 and the second addition circuit 204 are designed to add the same analog signal output from the two channels, thereby obtaining an analog signal that is twice the output of the single channel, thereby improving the signal-to-noise ratio of the analog signal. The signal is then filtered by a low-pass filter to reduce the distortion of the signal. The amplitude, frequency and other parameters of the DAC and DDS output signals can be controlled by the main control unit 100.

[0069] In order to improve the quality of the output low-frequency signal, the use of the precision digital-to-analog converter 201 is necessary. However, when the high-frequency signal is output, the sampling rate of the precision digital-to-analog converter 201 is generally low, and can only reach a sampling rate of 192kHz, resulting in few sampling points in each cycle. The precision digital-to-analog converter 201 used in this embodiment, when connected to the main control unit 100 through the I2S interface, can only achieve a sampling rate of 192kHz at most, that is, the maximum frequency output is only 80kHz. In order to achieve a frequency range of up to 1MHz, this embodiment uses a DDS chip as an output chip for high-frequency signals, which supports up to 80MHz sampling. The output of the DAC chip and the DDS chip is selected by controlling the second relay 205 through the main control unit 100, and a design shared by DAC and DDS is adopted, which takes into account the output quality of the low-frequency analog signal and the high-frequency analog signal to the greatest extent, and the maximum output frequency is increased to 1MHz, and the minimum output frequency reaches 0.05Hz, which meets the octave and fractional octave filter verification requirements.

[0070] like Figure 4 As shown, the multi-stage low-pass filter unit 300 includes a 1 MHz low-pass filter 301, a 200 KHz low-pass filter 302, an 80 KHz low-pass filter 303 and a 40 KHz low-pass filter 304 connected in sequence, the input end of the 1 MHz low-pass filter 301 is electrically connected to the output end of the audio data playback unit 200, the 1 MHz low-pass filter 301 and the 200 KHz low-pass filter 302 are electrically connected to the two static contacts of the third relay 305, respectively, the 80 KHz low-pass filter 303 and the 40 KHz low-pass filter 304 are electrically connected to the two static contacts of the fourth relay 306, respectively, the moving contact of the third relay 305 and the moving contact of the fourth relay 306 are electrically connected to the two static contacts of the fifth relay 307, the moving contact of the fifth relay 307 is electrically connected to the programmable precision attenuator unit 400, and the third relay 305, the fourth relay 306 and the fifth relay 307 are all electrically connected to the main control unit 100.

[0071] It should be noted that the multi-stage low-pass filter unit 300 refers to the analog signal output by the audio data playback unit 200, which is filtered by a multi-stage MFB filter circuit. The MFB filter can achieve different frequency responses by changing the resistance and capacitance values, making it suitable for various filtering requirements, from low-pass, high-pass to band-pass, band-stop and other filter designs. Moreover, the MFB filter usually has a higher quality factor, that is, the MFB filter can achieve a steep roll-off characteristic and better frequency selection performance.

[0072] In this embodiment, the maximum frequency of the sine wave signal is 1 MHz, and the multi-stage low-pass filter unit 300 is provided with four stages of low-pass filters of 1 MHz, 200 kHz, 80 kHz, and 40 kHz to filter the signal.

[0073] When the output signal frequency is above 200kHz and below 1MHz, the main control unit 100 connects the third relay 305 and the fifth relay 307 to the 1MHz low-pass filter 301, and the signal output by the audio data playback unit 200 passes through the 1MHz low-pass filter 301 and is output to the program-controlled precision attenuator unit 400;

[0074] When the output signal frequency is above 80kHz and below 200kHz, the main control unit 100 connects the third relay 305 and the fifth relay 307 to the 200kHz low-pass filter, and the signal output by the audio data playback unit 200 passes through the 1MHz low-pass filter 301 and the 200kHz low-pass filter, and then is output to the programmable precision attenuator unit 400.

[0075] When the output signal frequency is above 40kHz and below 80kHz, the main control unit 100 disconnects the third relay 305 and connects the fourth relay 306 and the fifth relay 307 to the 80kHz low-pass filter. The signal output by the audio data playback unit 200 passes through the 1MHz low-pass filter 301, the 200kHz low-pass filter and the 80kHz low-pass filter, and is output to the programmable precision attenuator unit 400.

[0076] When the output signal frequency is 40kHz or below, the main control unit 100 disconnects the third relay 305 and connects the fourth relay 306 and the fifth relay 307 to the 40kHz low-pass filter. The signal output by the audio data playback unit 200 passes through a 1MHz low-pass filter 301, a 200kHz low-pass filter, an 80kHz low-pass filter and a 40kHz low-pass filter, and then is output to the programmable precision attenuator unit 400.

[0077] In this embodiment, when the signal is output, the low-pass filter of the passband corresponding to the current signal frequency is selected through the third relay 305, the fourth relay 306 and the fifth relay 307, and then the signal is output, which can effectively ensure the quality of the signal output to reduce signal distortion.

[0078] like Figure 5As shown, the programmable precision attenuator unit 400 includes a sixth relay 401, a signal amplifier 402, a -10db attenuator 403, a precision operational amplifier 404 and a π-type resistor attenuation network 405, the moving contact of the sixth relay 401 is electrically connected to the output end of the low-pass filter unit, and the two static contacts of the sixth relay 401 are electrically connected to the seventh relay 406 and the -10db attenuator 403, wherein one of the static contacts of the sixth relay 401 is electrically connected to the moving contact of the seventh relay 406, and the two static contacts of the seventh relay 406 are electrically connected to the signal amplifier 402 and the single-ended electrical signal output bus 409, wherein the signal amplifier 402 is a 2x signal amplifier 402, and the signal amplifier 402 is The output end of the attenuator 402 is electrically connected to the single-ended electrical signal output bus 409, the output end of the -10 dB attenuator 403 is electrically connected to the precision operational amplifier 404, the output end of the precision operational amplifier 404 is electrically connected to the π-type resistor attenuation network 405, the π-type resistor attenuation network 405 is electrically connected to the single-ended electrical signal output bus 409 through a plurality of eighth relays 407, the single-ended electrical signal output bus 409 is connected to the BNC interface 500 and the single-ended to differential unit, the sixth relay 401, the seventh relay 406 and the eighth relay 407 are all connected to the main control unit 100, wherein the programmable precision attenuator unit 400 is mainly used to provide a 2-fold gain to the signal or to attenuate in a step unit of -10 dB. The attenuation amplitude of the output signal is controlled by the main control unit 100 through the eighth relay 407.

[0079] Since most precision operational amplifiers 404 generally have a relatively small output current in order to improve product performance and reduce product background noise, if the output of the precision operational amplifier 404 is directly connected to the π-type resistor attenuation network 405, when the output signal voltage amplitude is large, the output current of the precision operational amplifier 404 is insufficient, causing the signal to be unable to be fully output, increasing the distortion of the output signal and reducing the signal quality. Increasing the resistance of the π-type resistor attenuation network 405 will cause the output resistance of the system to be too high. Even if a follower is added after the π-type resistor attenuation network 405 to adjust the output impedance, it is still impossible to avoid the problems of high distortion, high background noise, low signal-to-noise ratio, etc. caused by adding a new active device at the signal output end.

[0080] In this embodiment, when the signal output voltage amplitude is large and does not need to be attenuated or high voltage output is required, the output of the precision operational amplifier 404 is disconnected from the π-type resistor attenuation network 405 through the eighth relay 407, and the precision operational amplifier 404 directly outputs the signal or directly outputs it after passing through the 2x signal amplifier 402, thereby avoiding the problem caused by insufficient output power when the precision operational amplifier 404 outputs a large signal. The 2x signal amplifier 402 is only connected when a large signal is output, and the connection of the 2x signal amplifier 402 is disconnected when a small signal is output, thereby ensuring the signal-to-noise ratio of the small signal to the greatest extent. At the same time, when the output signal voltage amplitude is large, since the π-type resistor attenuation network 405 is not connected, the circuit power consumption is further reduced and the heat generation is reduced.

[0081] Due to the performance problem of the operational amplifier, its electrical noise in the high frequency band is relatively large, so Figure 5 The signal amplifier 402 in the circuit adopts an MFB type low-pass filter circuit design with an amplification factor of 2 and a cut-off frequency of 1MHz. It does not affect the frequency response characteristics of the overall circuit, and can minimize the high-frequency interference that is most likely to occur in the circuit. The final amplifier circuit adopts a filter design concept, which supports the output of high-frequency (maximum 1MHz) sinusoidal signals while reducing the high-frequency noise in the circuit, so that the total distortion of the output signal is as low as less than 0.01% within the frequency range of 10Hz-40kHz.

[0082] When the signal needs to be attenuated, it first passes through the -10db attenuator 403 composed of resistors, and then uses the precision operational amplifier 404 to adjust the output impedance, and then connects to the π-type resistor attenuation network 405, and the output of the π-type resistor attenuation network 405 is controlled by the eighth relay 407. This scheme attenuates the maximum voltage amplitude of the signal connected to the π-type resistor attenuation network 405 by 10dB, so that the output current of the precision operational amplifier 404 is less than its maximum output current, ensuring the quality of the output signal. At the same time, the active device is designed at the front end of the π-type resistor attenuation network 405, which guarantees the high signal-to-noise ratio of the output signal and the low background noise of the system to the greatest extent.

[0083] Example 2

[0084] like Fig.10 As shown, a method for generating an audio signal according to Embodiment 2 of the present application includes:

[0085] S100, obtaining a signal type and signal parameters set by a user, wherein the signal type includes a sine signal, white noise, narrowband white noise, pink noise, narrowband pink noise, swept frequency sine wave, swept amplitude sine wave and burst tone, and the signal parameters include frequency, amplitude and attenuation;

[0086] S200, generating a specified signal according to the signal type and signal parameters, and outputting the signal to the multi-stage low-pass filter unit 300 through the audio data playback unit 200;

[0087] S300, according to the frequency of the signal, select the low-pass filter of the corresponding frequency in the multi-stage low-pass filter unit 300 to filter the signal, wherein, if the frequency of the signal is in the range of (200KHz-1MHz], select the 1MHz low-pass filter for filtering; if the frequency of the signal is in the range of (80KHz-200KHz], select the 1MHz low-pass filter and the 200KHz low-pass filter 302 to filter in sequence; if the frequency of the signal is in the range of (40KHz-80KHz], select the 1MHz low-pass filter, the 200KHz low-pass filter 302 and the 80KHz low-pass filter 303 to filter in sequence; if the frequency of the signal is in the range of (0KHz-40KHz], select the 1MHz low-pass filter, the 200KHz low-pass filter 302, the 80KHz low-pass filter 303 and the 40KHz low-pass filter 304 to filter in sequence;

[0088] S400, output the filtered signal to the program-controlled precision attenuation unit, use the program-controlled precision attenuation unit to amplify the filtered signal or attenuate it with a step unit of -10dB, and output the signal processed by the program-controlled precision attenuation unit through the BNC interface 500.

[0089] It should be noted that, for other specific implementations of the audio signal generating method in this embodiment, reference can be made to the specific implementations of the audio signal generating device described above, which will not be described again here to avoid redundancy.

[0090] The above are only preferred specific implementations of the present application; however, the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical solution and its improved ideas of the present application within the technical scope disclosed in the present application, which should be included in the protection scope of the present application.

Claims

1. An audio signal generating device, characterized in that: The invention comprises a main control unit, wherein the main control unit is electrically connected to an audio data playback unit, the audio data playback unit is electrically connected to a multi-stage low-pass filter unit, the multi-stage low-pass filter unit is electrically connected to a programmable precision attenuator unit, the output end of the programmable precision attenuator unit is electrically connected to a BNC interface, the multi-stage low-pass filter unit and the programmable precision attenuator unit are both control-connected to the main control unit, wherein the main control unit is used to calculate and generate a specified AC signal and output a signal through the audio data playback unit, and the main control unit is also used to control the multi-stage low-pass filter unit to select a low-pass filter of a corresponding frequency according to the frequency of the output signal and to control the attenuation amplitude of the signal by the programmable precision attenuator unit.

2. The audio signal generating device according to claim 1, characterized in that: It also includes a power management unit, which includes an isolated AC transformer circuit for connecting to the mains, the isolated AC transformer circuit is electrically connected to a rectifier and filter circuit, the rectifier and filter circuit is electrically connected to a rechargeable power supply and a linear voltage regulator circuit, the rechargeable power supply and the linear voltage regulator circuit are electrically connected to a main control unit, an audio data playback unit, a multi-stage low-pass filter unit and a programmable precision attenuator unit through a path selection module, wherein the path selection module is used to detect whether the isolated AC transformer circuit is connected to the mains, if not, it is powered by the rechargeable power supply, if connected to the mains, it is powered by the linear voltage regulator circuit.

3. The audio signal generating device according to claim 2, characterized in that: The path selection module includes a power detection module, a control module and a first relay, wherein the power detection module is used to detect whether the isolated AC transformer circuit is connected to the mains and send the detection result to the control module, and the control module is used to control the first relay to select a rechargeable power supply or a linear voltage regulator circuit for power supply according to the detection result.

4. The audio signal generating device according to claim 2, characterized in that: It also includes a shell, in which the main control unit, the audio signal playing unit, the multi-stage low-pass filter unit, the programmable precision attenuator unit and the power management unit are all arranged. The shell is embedded with an external power interface for connecting to the mains power, the input end of the isolated AC transformer circuit is electrically connected to the external power interface, and the BNC interface is arranged on the surface of the shell.

5. The audio signal generating device according to claim 4, characterized in that: The main control unit is also electrically connected to a touch screen and a control panel, and the touch screen and the control panel are both arranged on the surface of the shell.

6. The audio signal generating device according to claim 4 or 5, characterized in that: The main control unit is also electrically connected to a DB9 interface and an RJ45 interface, and both the DB9 interface and the RJ45 interface are arranged on the surface of the shell.

7. The audio signal generating device according to claim 1 or 2, characterized in that: The audio data playback unit includes a precision digital-to-analog converter and a direct digital frequency synthesizer, both of which are electrically connected to a main control unit, an output end of the precision digital-to-analog converter is electrically connected to a first adding circuit, an output end of the direct digital frequency synthesizer is electrically connected to a second adding circuit, the first adding circuit and the second adding circuit are electrically connected to two static contacts of a second relay respectively, a moving contact of the second relay is electrically connected to a differential-to-single-ended circuit, the second relay is control-connected to the main control unit, and the differential-to-single-ended circuit is electrically connected to a multi-stage low-pass filter unit.

8. The audio signal generating device according to claim 7, characterized in that: The multi-stage low-pass filter unit includes a 1MHz low-pass filter, a 200KHz low-pass filter, an 80KHz low-pass filter and a 40KHz low-pass filter connected in sequence, the input end of the 1MHz low-pass filter is electrically connected to the output end of the audio data playback unit, the 1MHz low-pass filter and the 200KHz low-pass filter are electrically connected to the two static contacts of the third relay, respectively, the 80KHz low-pass filter and the 40KHz low-pass filter are electrically connected to the two static contacts of the fourth relay, respectively, the moving contact of the third relay and the moving contact of the fourth relay are electrically connected to the two static contacts of the fifth relay, respectively, the moving contact of the fifth relay is electrically connected to the programmable precision attenuator unit, and the third relay, the fourth relay and the fifth relay are all electrically connected to the main control unit.

9. The audio signal generating device according to claim 8, characterized in that: The programmable precision attenuator unit includes a sixth relay, a signal amplifier, a -10db attenuator, a precision operational amplifier and a π-type resistance attenuation network. The moving contact of the sixth relay is electrically connected to the output end of the low-pass filter unit, the two static contacts of the sixth relay are electrically connected to the seventh relay and the -10db attenuator, respectively, the two static contacts of the seventh relay are electrically connected to the signal amplifier and the single-ended electrical signal output bus, the output end of the signal amplifier is electrically connected to the single-ended electrical signal output bus, the output end of the -10db attenuator is electrically connected to the precision operational amplifier, the output end of the precision operational amplifier is electrically connected to the π-type resistance attenuation network, the π-type resistance attenuation network is electrically connected to the single-ended electrical signal output bus through a plurality of eighth relays, the single-ended electrical signal output bus is connected to a BNC interface and a single-ended to differential unit, and the sixth relay, the seventh relay and the eighth relay are all controlled and connected to the main control unit.

10. A method for generating an audio signal, characterized in that: Used to control the audio signal generating device according to any one of claims 1 to 9, the method comprising: S100, obtaining a signal type and signal parameters set by a user, wherein the signal type includes a sine signal, white noise, narrowband white noise, pink noise, narrowband pink noise, a swept frequency sine wave, a swept amplitude sine wave and a burst tone, and the signal parameters include frequency, amplitude and attenuation; S200, generating a specified signal according to the signal type and signal parameters, and outputting the signal to a multi-stage low-pass filter unit through an audio data playback unit; S300, according to the frequency of the signal, select a low-pass filter of a corresponding frequency in the multi-stage low-pass filter unit to filter the signal, wherein, if the frequency of the signal is in the range of (200KHz-1MHz], select a 1MHz low-pass filter for filtering; if the frequency of the signal is in the range of (80KHz-200KHz], select a 1MHz low-pass filter and a 200KHz low-pass filter in sequence for filtering; if the frequency of the signal is in the range of (40KHz-80KHz], select a 1MHz low-pass filter, a 200KHz low-pass filter and an 80KHz low-pass filter in sequence for filtering; if the frequency of the signal is in the range of (0KHz-40KHz], select a 1MHz low-pass filter, a 200KHz low-pass filter, an 80KHz low-pass filter and a 40KHz low-pass filter in sequence for filtering; S400, outputting the filtered signal to the program-controlled precision attenuation unit, using the program-controlled precision attenuation unit to amplify the filtered signal or attenuate it in a step unit of -10dB, and outputting the signal processed by the program-controlled precision attenuation unit through a BNC interface.

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