Transcript Self-Calibrating Audio Signal Equalization Greg Burns Wade Lindsey

Self-Calibrating Audio
Signal Equalization
Greg Burns
Wade Lindsey
Kevin McLanahan
Jack Samet
Project Scope
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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.
The goal of this project is to automatically
calibrate an audio signal to compensate for these
effects.
Group 15 - Wade Lindsey
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Audio Fundamentals
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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 graphic equalizer can then be used to adjust
the amplifier input to compensate for any
deviations off flat-band response
Group 15 - Wade Lindsey
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Block Diagram
Sensor
Array
PIC
Microcontroller
Spectrum
Analyzer
Pink
Noise
Generator
Audio
Preamp
M
U
X
Group 15 - Wade Lindsey
Equalizer
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Block Diagram
Sensor
Array
PIC
Microcontroller
Spectrum
Analyzer
Pink
Noise
Generator
Audio
Preamp
M
U
X
Group 15 - Wade Lindsey
Equalizer
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Equalizer Specifications
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10 Bands (32, 64, 128, 256, 512, 1024, 2048,
4096, 8192, 16384 Hz)
Filters, input, and output constructed using
LM351 op-amps
Discrete components and 10kΩ DS1803 digital
potentiometers
Group 15 - Wade Lindsey
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10-Band Equalizer Circuit
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Built Equalizer
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Equalizer Response
 Frequency response of equalizer with varying
resistances tested with HP VEE.
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Block Diagram
Sensor
Array
PIC
Microcontroller
Spectrum
Analyzer
Pink
Noise
Generator
Audio
Preamp
M
U
X
Group 15 - Kevin McLanahan
Equalizer
10
Block Diagram
Sensor
Array
PIC
Microcontroller
Spectrum
Analyzer
Pink Noise
Generator
M
U
X
Equalizer
Audio
Preamp
Group 15 - Kevin McLanahan
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Pink Noise Specifications
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Creates pseudorandom digital noise for white
noise in first stage at 3dB/dec
Second stage pink noise filter at -3dB/dec
Frequency response 20 Hz – 20 kHz
33-bit resolution in shift register for
pseudorandom number generation
Line level output at 150mV rms
Group 15 - Kevin McLanahan
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Pink Noise Generation
 Equal voltage
per octave across
audio band.
 FFT of Pink
Noise viewed on
oscilloscope.
Group 15 - Kevin McLanahan
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Block Diagram
Sensor
Array
PIC
Microcontroller
Spectrum
Analyzer
Pink
Noise
Generator
Audio
Preamp
M
U
X
Group 15 - Kevin McLanahan
Equalizer
14
Block Diagram
Sensor
Array
PIC
Microcontroller
Pink
Noise
Generator
Spectrum
Analyzer
Audio
Preamp
M
U
X
Group 15 - Kevin McLanahan
Equalizer
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Spectrum Analyzer
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Samples input signal from microphone
Performs an FFT (Fast Fourier Transform)
algorithm to extract frequency components
Compares relative frequency levels to optimal
flat-band response
Samples microphone input at 19.2 μs
Sample length of 256 data points at 8-bit
resolution
Group 15 - Kevin McLanahan
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FFT Explained
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Implementing Cooley/Tukey FFT algorithm.
Has Big O of N log N
Takes Fourier matrix of power 2 (28 in our case)
Breaks into 2 log N matrices and performs
multiplications on roots of unity (e2πihk/N)
Ultimate result returns a vector with frequency,
phase, and magnitude information.
Group 15 - Kevin McLanahan
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Block Diagram
Sensor
Array
PIC
Microcontroller
Spectrum
Analyzer
Pink
Noise
Generator
Audio
Preamp
M
U
X
Group 15 - Greg Burns
Equalizer
18
Block Diagram
Sensor
Array
PIC
Microcontroller
Spectrum
Analyzer
Pink
Noise
Generator
Audio
Preamp
M
U
X
Group 15 - Greg Burns
Equalizer
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Microcontroller Software
Initialization
Mode
Sets all initial variables and
default settings.
Calibration
Mode
Outputs pink noise signal
through speakers, receives
spectral data from analyzer,
and adjusts equalizer to
compensate.
Operation
Mode
Resets MUX to audio source
and selects current room
location to compensate.
Group 15 - Greg Burns
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Initialization Mode
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Sets system timers and interrupts
Configures input and output pins
Defaults variables to initial conditions
Initializes I2C transfers
Sets digital pots to a predetermined ideal flatband response
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Calibration Mode
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Gathers data from spectrum analyzer output
Compares current frequency response peaks to
ideal response
Adjusts digital potentiometers based upon
previous comparison
Repeats until current frequency response and
ideal response fall within 5% tolerance
Calibrates for every room position
Group 15 - Greg Burns
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Operation Mode
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Switches audio source from pink noise to
preamp
Sets digital pots to specific values corresponding
to room location
Monitors Sensor Arrays for room location
variations
Group 15 - Greg Burns
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Block Diagram
Sensor
Array
PIC
Microcontroller
Spectrum
Analyzer
Pink
Noise
Generator
Audio
Preamp
M
U
X
Group 15 - Jack Samet
Equalizer
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Future Improvements
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Increased number of frequency bands on EQ
Use of DSP processor for improved FFT
performance
Use of audio-grade tolerance components
Allow for wide variety of sensor array
configurations
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Conclusions
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Economically feasible and marketable
Modular design allows for easy implementation,
innovation, and reproduction
Compatible with most modern stereo systems
Overall a universally usable product from
personal to commercial applications
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Questions?
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Fin
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