Guitar Effects Processor Using DSP – Project Update

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Guitar Effects Processor Using DSP – Project Update Powered By Docstoc
					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
Results and Conclusions
            Overview
Overall Project
GUI Interface
Filter Design
Results and Conclusions
Overall Project
         • Guitar signal to DSP
         • Passes through filters
         • User controls filters
         through GUI
         • Signal outputs to speaker
           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
Noise Filter
– Eliminates 60-Hz hum from single-coil pickups
– Sampling rate made design difficult
     Pole and zero practically overlap




        Z-Transform Function if sampling rate = 48000
     Multiband approach considered
       Cancelled: Noise Filter
FFT of signal shows pointlessness of filter




 FFT of Strat: A-110 Hz     Noise Component of Strat Signal
            Guitars Used
Squier Stratocaster
– 3 Single-coil pickups
– 5-way selector switch
Squier Telecaster Custom
– 2 Humbucker pickups
– 3-Way Selector Switch
          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
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
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
            Overview
Overall Project
GUI Interface
Filter Design
Results and Conclusions
                  GUI
Allows user to select and control effects
Interface simple and easy to use
GUI Software Design
           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
Tying GUI and simulink
Sample testing (no effects)
Sample test (with effects used)
             Overview
Recap of Overall Project
GUI Interface
Filter Design
Results and Conclusions
            Filter Design: Overview
  8 user-modifiable filters
• Distortion
• Volume Envelope
• Octaver
• Flanger                     Control Signal: A @
                              110 Hz
• Phase Shifter
• Chorus
• Delay/Echo
• Reverb
     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
Signal attack is eliminated
Violin-type sound
 – Signal gradually approachs full value
 – Does so for each plucked note
      Filter Design: Octaver
Octave Down
– Halves frequency of signal
– Output at same speed as input




              A @ 55 Hz from MATLAB Code
         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
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
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: Chorus
                    Simulink Model
                    of Chorus
   Filter Design: Delay/Echo
Signal is split
Fixed delay determined by user




                             Audio Test of Delay/Echo


      Delay/Echo Model
          Filter Design: Reverb
Delay-based filter
– Attenuated feedback decays sound
– Delay determines length of decay




                                  -4
                                 z

     Discrete                   Delay
     Impulse

                          0.8

                        Gain



                                          Scope



                     Reverb Test Filter
             Overview
Recap of Overall Project
GUI Interface
Filter Design
Results and Conclusions
                     Results
MATLAB
–   5 of 8 effects fully functional
–   Octaver slows signal
–   Volume Envelope only for first note
–   Phase Shifter not adding any effect
                   Results
GUI
– Connection to Simulink easier versus direct hard-
  coding
– No real-time application, but Simulink connection is
  the step before that
                  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
                 Results
Real-time demo
            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
             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
              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…
We were able to bring the house down!!!
Questions?

				
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posted:8/16/2011
language:English
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