1.1 Introduction
With the development of industrial production, transportation, urban construction, and population density, the increase in household facilities (audio, air conditioning, television, etc.) and environmental noise have become increasingly serious, and it has become a major public pollution of the human social environment. Therefore, the monitoring of environmental noise has become a closely watched issue. The real-time noise spectrum analyzer is an indispensable device for measuring and analyzing noise signals. It is a common tool for professional noise monitoring and audio signal research and application. It is widely used.
The traditional analog audio spectrum analyzer has obvious shortcomings. The hardware implementation is complicated. It can only measure the amplitude of the frequency, lacks the phase information, and is bulky. It is inconvenient to carry and cannot be measured in real time in complex noise scenes. Requirements for modern environmental noise measurements. A modern spectrum analyzer based on Fast Fourier Transform (FFT) decomposes the measured signal into discrete frequency components by Fourier operation to achieve the same results as traditional spectrum analyzers. The new spectrum analyzer uses a digital method to directly sample the input signal by an analog/digital converter (ADC), and then obtains a spectrum distribution map through FFT processing to realize audio spectrum analysis.
1.2 Project Background / Motivation
The AVR EVK1105 development kit used in this project is based on the AT32UC3A0512 microcontroller. It has a built-in hardware multiplier, supports DSP instruction set, 64K SRAM, and has powerful fixed-point computing capability, so it can fully meet the data operation requirements in digital signal processing; and AVR The EVK1105 development kit is equipped with TLV320AIC23B low-power stereo audio codec chip, supports MIC and LINE IN input modes, and has programmable gain adjustment for both input and output. Integrated analog-to-digital conversion (ADC) components are available in 8K. Provides 16-bit sampling in the frequency range of 96K, which can achieve high data sampling accuracy; QVGA (320*240) full-color LCD display can well display the waveform and spectrum of noise signals and good users interface.
Therefore, the project makes full use of the hardware and software resources provided by the AVR EVK1105 development kit, and implements a real-time noise spectrum analyzer based on Wi-Fi control by digital signal processing. The real-time noise spectrum analyzer adopts a digital method to directly obtain sampling data from an analog/digital converter (ADC), and uses a FIR digital filtering algorithm and an FFT algorithm to obtain a spectrum distribution map of a real-time noise signal, and simultaneously calculates a noise-related parameter, and realizes Real-time noise measurement and analysis. The noise spectrum analyzer achieves good linearity and high resolution, and adds Wi-Fi wireless control modules to perform complex noise and field noise measurement tasks in unattended environments. The device is small in size, easy to operate, and easy to carry.
Second, the demand analysis2.1 Functional requirements
1) Realize the parameter measurement function of the input noise signal:
a) display a real-time waveform of the noise signal;
b) displaying the octave and 1/3 octave spectrum of the real-time noise signal;
c) Measuring the relevant parameters of the real-time noise signal:
?? Sound pressure level Lp based on A, C, Z weighted noise signals;
??Maximum, minimum sound pressure level measurement (A, C weighting), peak sound pressure level (C weighting), equivalent continuous sound pressure level Leq (A, C weighting);
?? Noise signal cumulative percentage n sound level Ln (A, C weighted);
2) Wi-Fi-based wireless network connection to achieve remote device control and achieve noise measurement in an unmanned environment;
3), SD card to achieve data storage, playback function;
4) Calibration: Acoustic calibration, calibrated with a sound calibrator.
2.2 Performance requirements
(1) Measurement range: 30~120dB;
(2) octave bandwidth: 31.5~16KHz;
(3) 1/3 octave bandwidth: 20Hz~20KHz;
(4) Frequency resolution: 20Hz;
Third, the program design3.1 System function realization principle
The system mainly uses the audio data input interface or microphone of AVR EVK1105 development board to obtain noise signal data, and uses the TVL3230AIC23B low-power stereo audio codec chip on the development board to realize 16-bit A/D conversion to realize analog signal to Digital signal conversion, and use the DSP instruction set of AT32UC3A0512 to realize FIR digital filtering and FFT algorithm, obtain the spectrum data of the audio signal, calculate the relevant parameters of the audio signal, and display it on the full-color LCD screen on the development board in real time. Waveforms, spectrograms, and values ​​of related parameters of the noise signal. The collected data can also be stored in the SD card slot through the SD card slot on the development board for subsequent data playback and analysis.
The system also supports Wi-Fi-based wireless network interface for remote control operation of the device, such as measurement parameter setting, measurement start and stop commands, etc., to achieve measurement of noise parameters in an unmanned environment. Thereby completing the monitoring and analysis function of the noise signal.
The system hardware block diagram is shown in Figure 1:
Figure 1 system hardware block diagram
3.2 Hardware platform selection and resource configuration
1. Hardware platform:
The system uses the AVR EVK1105 development board, and the AVR EVK1105 is an evaluation kit based on the AT32UC3A0512.
EVK1105 development board hardware resources use:
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