2. Guitar Effects Processor Using DSP
Alex Czubak
Gorav Raheja
Advisor: Dr. Thomas L. Stewart

3. Problems
Need for real-time effects generation for live performances and recording
Effects pedals exist, but better used for presets

4. Overview Overall Project GUI Interface Filter Design
Results and Conclusions

5. Overview Overall Project GUI Interface Filter Design
Results and Conclusions

6. Overall Project Guitar signal to DSP Passes through filters
User controls filters through GUI
Signal outputs to speaker

7. 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

8. 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

9. Cancelled: Noise Filter
FFT of signal shows pointlessness of filter
FFT of Strat: A-110 Hz
Noise Component of Strat Signal

10. 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

11. 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

12. 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

13. 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

14. Overview Overall Project GUI Interface Filter Design
Results and Conclusions

15. GUI Allows user to select and control effects
Interface simple and easy to use

16. GUI Software Design

17. 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

18. Tying GUI and simulink

19. Sample testing (no effects)

20. Sample test (with effects used)

21. Overview Recap of Overall Project GUI Interface Filter Design
Results and Conclusions

22. Filter Design: Overview
8 user-modifiable filters
Distortion
Volume Envelope
Octaver
Flanger
Phase Shifter
Chorus
Delay/Echo
Reverb
Control Signal: 110 Hz

23. 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

24. Filter Design: Volume Envelope
Signal attack is eliminated
Violin-type sound
Signal gradually approachs full value
Does so for each plucked note

25. Filter Design: Octaver
Octave Down
Halves frequency of signal
Output at same speed as input
55 Hz from MATLAB Code

26. 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

27. 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

28. 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

29. Filter Design: Chorus
Simulink Model of Chorus

30. Filter Design: Delay/Echo
Signal is split
Fixed delay determined by user
Audio Test of Delay/Echo
Delay/Echo Model

31. Filter Design: Reverb Delay-based filter
Attenuated feedback decays sound
Delay determines length of decay
Reverb Test Filter

32. Overview Recap of Overall Project GUI Interface Filter Design
Results and Conclusions

33. Results MATLAB 5 of 8 effects fully functional Octaver slows signal
Volume Envelope only for first note
Phase Shifter not adding any effect

34. Results GUI Connection to Simulink easier versus direct hard-coding
No real-time application, but Simulink connection is the step before that

35. 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

36. Results
Real-time demo

37. 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

38. 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

39. 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

40. And so…
We were able to bring the house down!!!

41. Questions?