S14: Spectrum Analyzer for Audio Frequency Signals
Contents
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Spectrum Analyzer for Audio Frequency Signals
Abstract
We plan to build a Spectrum Analyzer for Audio Frequency signals. Our device is able to display frequencies in audio of up to 4 kHz, which covers the most of the of the frequency range of typical music. The main inspiration for our project was applications of Music visualizers which are seen in many softwares like Windows Media Player.
Introduction
A Spectrum analyzer is used in measuring the magnitude of an input signal versus a frequency for a certain frequency range of an instrument. The primary use of a Spectrum analyzer is to measure power of spectrum of unknown or known signals. An input signal that a spectrum analyzer measure is electrical, however, signals like acoustic pressure or optical waves can also be measured by use of an appropriate transducer.
By analyzing the spectra of electrical signals, dominant frequency, power, distortion, harmonics, bandwidth, and other spectral components of a signal can be observed that are not easily detectable in time domain waveforms. These parameters are useful in the characterization of electronic devices, such as wireless transmitters.
The display of a Spectrum analyzer has frequency on the horizontal axis and the amplitude displayed on the vertical axis. In general observation, a Spectrum analyzer looks like an oscilloscope and, in fact, some lab instruments can function either as an oscilloscope or a spectrum analyzer.
Objectives
The main objective of our project was to display the audio input given to the mic through an LED display. The range of frequency was kept to 4K Hz as it covers most of the frequency range for a typical musical instrument. The LED matrix will be able to display change in the audio signal correspondingly.
The scope of the project was divided into 3 main parts :
- ADC interfacing with the audio input through mic
- Performing FFT calculations on the LPC1758 board and communication of the same to LED matrix.
- Interfacing of the 16 X 32 LED matrix with LPC1758 board
Team Members & Responsibilities
- Anand Dumbre
- ADC interfacing + LED Interfacing
- Chinmay Vaidya
- Fast Fourier Transforms + Hardware.
- Kevin Beadle
- LED interfacing
Schedule
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| Week# | Date | Planned Task | Actual Task |
|---|---|---|---|
| 1 | 03/13/14 | Order & receive parts. | Ordered the parts.late by 1 week as parts were not available |
| 2 | 03/20/14 | Interface microphone/LED strip to SJ One board. | Obtained the parts. Started work on Microphone and LED. |
| 3 | 03/27/14 | Design band pass filter to reduce noise. | Done |
| 4 | 04/03/14 | Analyze audio signals with Matlab using FFT. | The waveforms were not coming out properly. FFT code was working alright |
| 5 | 04/10/14 | Write code to process audio signal on SJ One board. | FFT code working fine. |
| 6 | 04/17/14 | Write algorithm to output audio signal to LED strip. | ADC and FFT output coming out properly |
| 7 | 04/24/14 | Test algorithm using different audio sources. | Tested using various Youtube audio. Still working on porting of LED strip. |
| 8 | 05/01/14 | Finalize project firmware. | |
| 9 | 05/08/14 | Finalize project demonstration. | |
| 10 | 05/13/14 | Finalize project report. |
Parts List & Cost
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| Component Name | Quantity | Cost per Item | Total Cost |
|---|---|---|---|
| Audio Amplifier Board | 1 | 25$ | 25$ |
| LPC1758 Board | 2 | 70$ | 140$ |
| LED Matrix (16 X 32) | 1 | 35$ | 35$ |
| Wires | 50 | 0.5$ | 25$ |
Design & Implementation
Hardware Design
The flow of our Hardware datapath is very linear. The audio board with Mic was interfaced with the LPC1758 board by connecting the audio, envelope, gate,Vcc and Ground ports to the board. The input from mic is fed to the ADC on the board. The ADC is internally connected to the processor. The FFT calculations are done on the board and the output of the FFT is given to other LPC1758 board by UART communication. The LPC1758 board is interfaced with the LED matrix. The block diagram of our Spectrum analyzer hardware is shown below.
Each block diagram hardware design will be explained as follows:
- Audio Input : The audio input can be provided by playing a song or even just by talking into the mic
- Audio Amp & Filter design: The audio amp board had an in-built mic which provided the input. Filter design was implemented and the filter was direct connected to the audio board. The filter design was implemented as shown in the image.
- LPC1758 Board (ADC + FFT): The LPC1758 board has an in-built ADC. The output from audio board is connected to ADC of the board. The audio, envelope, gate, Vcc and ground ports from audio board will be connected to ADC ports. All the FFT calculations are software based and computed directly on the processor.
- LPC1758 Board (for LED matrix interfacing) : The communication between the two LPC1758 boards is done by UART. The UART communication uses Tx and Rx ports of both the boards.
- 16 x 32 LED Matrix : The LED matrix is connected to LPC1758 board by connecting the A,B,C,R1,B1,R2,B2,G1,G2,Clk,OE and Latency of the Matrix to the port pins of LPC1758 board. The connections is as shown in the image below.
File:Spring14 SpectrumAnalyzer1.jpgFile:Spring14 SpectrumAnalyzer2.jpg
Hardware Interface
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Software Design
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Implementation
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Testing & Technical Challenges
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Include sub-sections that list out a problem and solution, such as:
My Issue #1
The main issue was obtaining correct parts for the audio amplifier board and LED strip. The gain of amplifier needed to correct for required frequency. Also, the parts were not available on Websites. Resolution: checked the forums on the websites to obtain more information about the boards. Placed an order for deliver when available on the Adafruit and Sparkfun.
My Issue #2
We required the timer1 for ADC. However, the timer1 was configured for the I2C bus. Hence, we changed the I2C bus ports to timer2 and used the timer1 for ADC
My Issue #3
Adafruit Led strip had a library for Arduino. We need to port it to LPC in order to get our LED strip working.However, there are timing issues as the clock frequencies are not same for both. Issue is not resolved yet.
Conclusion
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Project Video
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Project Source Code
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References
Acknowledgement
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References Used
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Appendix
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