1. Self-Calibrating Audio Signal Equalization Greg Burns Wade Lindsey Kevin McLanahan Jack Samet

2. 2Group 15 - Wade Lindsey Project Scope In any closed room, standing waves exist that change the way audio signals arrive at the ear. In any closed room, standing waves exist that change the way audio signals arrive at the ear. Variations in amplifier design, speaker efficiency, and room geometry affect the frequency response, degrading it from flat-band operation. Variations in amplifier design, speaker efficiency, and room geometry affect the frequency response, degrading it from flat-band operation. The goal of this project is to automatically calibrate an audio signal to compensate for these effects. The goal of this project is to automatically calibrate an audio signal to compensate for these effects.

3. 3Group 15 - Wade Lindsey Audio Fundamentals Pink Noise is a randomly generated signal that exhibits a constant voltage per octave. Pink Noise is a randomly generated signal that exhibits a constant voltage per octave. A spectrum analyzer can be used to obtain the actual frequency response of an audio signal when placed in a test position in a room. A spectrum analyzer can be used to obtain the actual frequency response of an audio signal when placed in a test position in a room. A graphic equalizer can then be used to adjust the amplifier input to compensate for any deviations off flat-band response A graphic equalizer can then be used to adjust the amplifier input to compensate for any deviations off flat-band response

4. 4Group 15 - Wade Lindsey Block Diagram Spectrum Analyzer PIC Microcontroller Pink Noise Generator Audio Preamp MUXMUX Equalizer Sensor Array

5. 5Group 15 - Wade Lindsey Block Diagram Spectrum Analyzer PIC Microcontroller Pink Noise Generator Audio Preamp MUXMUX Equalizer Sensor Array

6. 6Group 15 - Wade Lindsey Equalizer Specifications 10 Bands (32, 64, 128, 256, 512, 1024, 2048, 4096, 8192, 16384 Hz) 10 Bands (32, 64, 128, 256, 512, 1024, 2048, 4096, 8192, 16384 Hz) Filters, input, and output constructed using LM351 op-amps Filters, input, and output constructed using LM351 op-amps Discrete components and 10kΩ DS1803 digital potentiometers Discrete components and 10kΩ DS1803 digital potentiometers

7. 7Group 15 - Wade Lindsey 10-Band Equalizer Circuit

8. 8Group 15 - Wade Lindsey Built Equalizer

9. 9Group 15 - Wade Lindsey Equalizer Response  Frequency response of equalizer with varying resistances tested with HP VEE.

10. 10Group 15 - Kevin McLanahan Block Diagram Spectrum Analyzer PIC Microcontroller Pink Noise Generator Audio Preamp MUXMUX Equalizer Sensor Array

11. 11Group 15 - Kevin McLanahan Block Diagram Spectrum Analyzer PIC Microcontroller Pink Noise Generator Audio Preamp MUXMUX Equalizer Sensor Array

12. 12Group 15 - Kevin McLanahan Pink Noise Specifications Creates pseudorandom digital noise for white noise in first stage at 3dB/dec Creates pseudorandom digital noise for white noise in first stage at 3dB/dec Second stage pink noise filter at -3dB/dec Second stage pink noise filter at -3dB/dec Frequency response 20 Hz – 20 kHz Frequency response 20 Hz – 20 kHz 33-bit resolution in shift register for pseudorandom number generation 33-bit resolution in shift register for pseudorandom number generation Line level output at 150mV rms Line level output at 150mV rms

13. 13Group 15 - Kevin McLanahan Pink Noise Generation  Equal voltage per octave across audio band.  FFT of Pink Noise viewed on oscilloscope.

14. 14Group 15 - Kevin McLanahan Block Diagram Spectrum Analyzer PIC Microcontroller Pink Noise Generator Audio Preamp MUXMUX Equalizer Sensor Array

15. 15Group 15 - Kevin McLanahan Block Diagram Spectrum Analyzer PIC Microcontroller Pink Noise Generator Audio Preamp MUXMUX Equalizer Sensor Array

16. 16Group 15 - Kevin McLanahan Spectrum Analyzer Samples input signal from microphone Samples input signal from microphone Performs an FFT (Fast Fourier Transform) algorithm to extract frequency components Performs an FFT (Fast Fourier Transform) algorithm to extract frequency components Compares relative frequency levels to optimal flat-band response Compares relative frequency levels to optimal flat-band response Samples microphone input at 19.2 μs Samples microphone input at 19.2 μs Sample length of 256 data points at 8-bit resolution Sample length of 256 data points at 8-bit resolution

17. 17Group 15 - Kevin McLanahan FFT Explained Implementing Cooley/Tukey FFT algorithm. Implementing Cooley/Tukey FFT algorithm. Has Big O of N log N Has Big O of N log N Takes Fourier matrix of power 2 (2 8 in our case) Takes Fourier matrix of power 2 (2 8 in our case) Breaks into 2 log N matrices and performs multiplications on roots of unity (e 2πihk/N ) Breaks into 2 log N matrices and performs multiplications on roots of unity (e 2πihk/N ) Ultimate result returns a vector with frequency, phase, and magnitude information. Ultimate result returns a vector with frequency, phase, and magnitude information.

18. 18Group 15 - Greg Burns Block Diagram Spectrum Analyzer PIC Microcontroller Pink Noise Generator Audio Preamp MUXMUX Equalizer Sensor Array

19. 19Group 15 - Greg Burns Block Diagram Spectrum Analyzer PIC Microcontroller Pink Noise Generator Audio Preamp MUXMUX Equalizer Sensor Array

20. 20Group 15 - Greg Burns Microcontroller Software Initialization Mode Calibration Mode Operation Mode Sets all initial variables and default settings. Outputs pink noise signal through speakers, receives spectral data from analyzer, and adjusts equalizer to compensate. Resets MUX to audio source and selects current room location to compensate.

21. 21Group 15 - Greg Burns Initialization Mode Sets system timers and interrupts Sets system timers and interrupts Configures input and output pins Configures input and output pins Defaults variables to initial conditions Defaults variables to initial conditions Initializes I 2 C transfers Initializes I 2 C transfers Sets digital pots to a predetermined ideal flat- band response Sets digital pots to a predetermined ideal flat- band response

22. 22Group 15 - Greg Burns Calibration Mode Gathers data from spectrum analyzer output Gathers data from spectrum analyzer output Compares current frequency response peaks to ideal response Compares current frequency response peaks to ideal response Adjusts digital potentiometers based upon previous comparison Adjusts digital potentiometers based upon previous comparison Repeats until current frequency response and ideal response fall within 5% tolerance Repeats until current frequency response and ideal response fall within 5% tolerance Calibrates for every room position Calibrates for every room position

23. 23Group 15 - Greg Burns Operation Mode Switches audio source from pink noise to preamp Switches audio source from pink noise to preamp Sets digital pots to specific values corresponding to room location Sets digital pots to specific values corresponding to room location Monitors Sensor Arrays for room location variations Monitors Sensor Arrays for room location variations

24. 24Group 15 - Jack Samet Block Diagram Spectrum Analyzer PIC Microcontroller Pink Noise Generator Audio Preamp MUXMUX Equalizer Sensor Array

25. 25Group 15 - Jack Samet Future Improvements Increased number of frequency bands on EQ Increased number of frequency bands on EQ Use of DSP processor for improved FFT performance Use of DSP processor for improved FFT performance Use of audio-grade tolerance components Use of audio-grade tolerance components Allow for wide variety of sensor array configurations Allow for wide variety of sensor array configurations

26. 26Group 15 - Jack Samet Conclusions Economically feasible and marketable Economically feasible and marketable Modular design allows for easy implementation, innovation, and reproduction Modular design allows for easy implementation, innovation, and reproduction Compatible with most modern stereo systems Compatible with most modern stereo systems Overall a universally usable product from personal to commercial applications Overall a universally usable product from personal to commercial applications

27. 27Group 15 Questions?

28. 28Group 15 Fin