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Guitar Effects Processor Using DSP
Alex Czubak Gorav Raheja Advisor: Dr. Thomas L. Stewart
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Problems Need for real-time effects generation for live performances and recording Effects pedals exist, but better used for presets
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Overview Overall Project GUI Interface Filter Design
Results and Conclusions
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Overview Overall Project GUI Interface Filter Design
Results and Conclusions
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Overall Project Guitar signal to DSP Passes through filters
User controls filters through GUI Signal outputs to speaker
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Project Specs 8 Effects filters in both parallel and series
Sampling Rate = 48,000 samples/sec GUI controls effects filters Real-time processing at a speed at most 1/sampling rate
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Cancelled Original Spec
Noise Filter Eliminates 60-Hz hum from single-coil pickups Sampling rate made design difficult Pole and zero practically overlap Multiband approach considered Z-Transform Function if sampling rate = 48000
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Cancelled: Noise Filter
FFT of signal shows pointlessness of filter FFT of Strat: A-110 Hz Noise Component of Strat Signal
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Guitars Used Squier Stratocaster Squier Telecaster Custom
3 Single-coil pickups 5-way selector switch Squier Telecaster Custom 2 Humbucker pickups 3-Way Selector Switch
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Amplifiers Used Fender Frontman 15R Guitar Amplifier
External Reverberation Potentiometer set to 0 so designed Reverberation effects can be tested Distortion channel, ignored to test designed filter Output: 15 watts into 8 ohms
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DSP Board Used Spectrum Digital TMS320C6713 DSK
DSP Chip: Texas Instruments 225 MHz 16 MB SDRAM 512 KB Flash Memory AIC23 Stereo Codec allowing 8-kHz to 96-kHz sampling rate A/D and D/A Converters only handle 2 Volt amplitude max
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Programs Used MATLAB and Simulink Code Composer 3.1
Quick conversion of audio for testing Graphical modeling of filters GUI design links with models Auto C-code generation for DSP board Code Composer 3.1 Programs code to board Only way to interface with board
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Overview Overall Project GUI Interface Filter Design
Results and Conclusions
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GUI Allows user to select and control effects
Interface simple and easy to use
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GUI Software Design
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GUI Testing Initial examples to understand GUI in MATLAB
Uploading/playing wave files Tying GUI through Simulink models Connecting GUI through Simulink to DSP board for “real time” implementation
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Tying GUI and simulink
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Sample testing (no effects)
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Sample test (with effects used)
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Overview Recap of Overall Project GUI Interface Filter Design
Results and Conclusions
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Filter Design: Overview
8 user-modifiable filters Distortion Volume Envelope Octaver Flanger Phase Shifter Chorus Delay/Echo Reverb Control Signal: 110 Hz
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Filter Design: Distortion
Boosts and clips signal Gain values from 1 to 50 Saturation at -0.5 and +0.5 Telecaster – A 5th Chord Simulink Distortion Model
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Filter Design: Volume Envelope
Signal attack is eliminated Violin-type sound Signal gradually approachs full value Does so for each plucked note
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Filter Design: Octaver
Octave Down Halves frequency of signal Output at same speed as input 55 Hz from MATLAB Code
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Filter Design: Flanger
Signal is split Passed through variable-time delay Controlled by sine wave at <= 1 Hz Maximum delay = 10 ms Flanged “NBC” Simulink Model of Flanger Effect Filter
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Filter Design: Phase Shifter
Similar to Flanger, but: All-pass filter instead of just delay Creates non-linearly spaced notches 2 filters = 1 notch 8 filters for 4 notches
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Filter Design: Chorus Similar to Flanger, but: 4 splits instead of 1
Creates multi-guitar sound User selects how many are on Sine waves run at 3 Hz and 6 Hz
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Filter Design: Chorus Simulink Model of Chorus
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Filter Design: Delay/Echo
Signal is split Fixed delay determined by user Audio Test of Delay/Echo Delay/Echo Model
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Filter Design: Reverb Delay-based filter
Attenuated feedback decays sound Delay determines length of decay Reverb Test Filter
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Overview Recap of Overall Project GUI Interface Filter Design
Results and Conclusions
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Results MATLAB 5 of 8 effects fully functional Octaver slows signal
Volume Envelope only for first note Phase Shifter not adding any effect
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Results GUI Connection to Simulink easier versus direct hard-coding
No real-time application, but Simulink connection is the step before that
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Results Real-Time 3 of 8 effects work properly
3 have variable-time delay issue “Popping” occurs Happens if effect is present in system 2 haven’t been finalized in Simulink
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Results Real-time demo
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Conclusions Effects Simulink and Code Composer allow quick real-time development Real-time variable-time delay a complicated matter Embedded M-file block not a simple solution for Volume Envelope
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Conclusions GUI Significant learning curve at first
Need to define all variables from workspace if used No info on connecting GUI to DSP board Simulation environment demonstrated good functionality
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Conclusions Future Ideas Effects GUI
Improved variable-time delay algorithm for DSP Board Add more effects to system Wah-wah Talk-Box Add pedal functionality to select effects on the fly USB or PC Card connection to laptop for portability GUI Allow real-time implementation More variable control for more dynamic effects
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And so… We were able to bring the house down!!!
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Questions?
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