Guitar Effects Processor Using DSP

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(No Transcript)
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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
• 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 C6713 _at_ 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
• 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 A _at_ 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

A _at_ 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 lt 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 havent 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
• 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?