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Guitar Effects Processor Using DSP. Alex Czubak Gorav Raheja Advisor: Dr. Thomas L. Stewart. Problems. Need for real-time effects generation for live performances and recording Effects pedals exist, but better used for presets. Overview. Overall Project GUI Interface Filter Design

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guitar effects processor using dsp

Guitar Effects Processor Using DSP

Alex Czubak

Gorav Raheja

Advisor: Dr. Thomas L. Stewart

problems
Problems
  • Need for real-time effects generation for live performances and recording
  • Effects pedals exist, but better used for presets
overview
Overview
  • Overall Project
  • GUI Interface
  • Filter Design
  • Results and Conclusions
overview5
Overview
  • Overall Project
  • GUI Interface
  • Filter Design
  • Results and Conclusions
overall project
Overall Project
  • Guitar signal to DSP
  • Passes through filters
  • User controls filters through GUI
  • Signal outputs to speaker
project specs
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
cancelled original spec
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

cancelled noise filter
Cancelled: Noise Filter
  • FFT of signal shows pointlessness of filter

FFT of Strat: A-110 Hz

Noise Component of Strat Signal

guitars used
Guitars Used
  • Squier Stratocaster
    • 3 Single-coil pickups
    • 5-way selector switch
  • Squier Telecaster Custom
    • 2 Humbucker pickups
    • 3-Way Selector Switch
amplifiers used
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
dsp board used
DSP Board Used
  • Spectrum Digital TMS320C6713 DSK
    • DSP Chip: Texas Instruments C6713 @ 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
programs used
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
overview14
Overview
  • Overall Project
  • GUI Interface
  • Filter Design
  • Results and Conclusions
slide15
GUI
  • Allows user to select and control effects
  • Interface simple and easy to use
gui testing
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
overview21
Overview
  • Recap of Overall Project
  • GUI Interface
  • Filter Design
  • Results and Conclusions
filter design overview
Filter Design: Overview
  • 8 user-modifiable filters
  • Distortion
  • Volume Envelope
  • Octaver
  • Flanger
  • Phase Shifter
  • Chorus
  • Delay/Echo
  • Reverb

Control Signal: A @ 110 Hz

filter design distortion
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

filter design volume envelope
Filter Design: Volume Envelope
  • Signal attack is eliminated
  • Violin-type sound
    • Signal gradually approachs full value
    • Does so for each plucked note
filter design octaver
Filter Design: Octaver
  • Octave Down
    • Halves frequency of signal
    • Output at same speed as input

A @ 55 Hz from MATLAB Code

filter design flanger
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

filter design phase shifter
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
filter design chorus
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
filter design chorus29
Filter Design: Chorus

Simulink Model of Chorus

filter design delay echo
Filter Design: Delay/Echo
  • Signal is split
  • Fixed delay determined by user

Audio Test of Delay/Echo

Delay/Echo Model

filter design reverb
Filter Design: Reverb
  • Delay-based filter
    • Attenuated feedback decays sound
    • Delay determines length of decay

Reverb Test Filter

overview32
Overview
  • Recap of Overall Project
  • GUI Interface
  • Filter Design
  • Results and Conclusions
results
Results
  • MATLAB
    • 5 of 8 effects fully functional
    • Octaver slows signal
    • Volume Envelope only for first note
    • Phase Shifter not adding any effect
results34
Results
  • GUI
    • Connection to Simulink easier versus direct hard-coding
    • No real-time application, but Simulink connection is the step before that
results35
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
results36
Results
  • Real-time demo
conclusions
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
conclusions38
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
conclusions39
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
and so
And so…

We were able to bring the house down!!!