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

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Presentation on theme: "Guitar Effects Processor Using DSP Alex Czubak Gorav Raheja Advisor: Dr. Thomas L. Stewart."— Presentation transcript:

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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 HzNoise Component of Strat Signal

10 Guitars Used Squier Stratocaster –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 –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 5 th 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 Simulink Model of Flanger Effect Filter Flanged “NBC”

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 Delay/Echo Model Audio Test of Delay/Echo

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 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?


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