Guitar Effects Generator Using DSP

By: Alex CzubakGorav Raheja

Advisor: Dr. Thomas L. Stewart

Outline Of Presentation

• Project Summary

• Patents and Standards

• Detailed Project Description

• Equipment And Parts List

• Schedule Of Tasks

Project Summary

• Creation of sound effects using digital signal processing

• Guitar sends audio signal

• Signal is modified and processed on DSP through effects filters

• User controls which effects and to what degree through GUI

Patents

• US Patent 6664460 – System for customizing musical effects using digital signal processing techniques, December 16, 2003

• US Patent 0147050 – System for simulating sound engineering effects, July 6, 2006

Project Description

• Guitars and Amplifier

• DSP Board

• GUI

• Filter Designs

Project Description

• Guitars and Amplifier

• DSP Board

• GUI

• Filter Designs

Guitars

• #1- Squier Stratocaster– 3 single-coil pickups– Produce clean lean sound– 60hz noise signal along with audio signal

Guitars

0 200 400 600 800 1000 1200 1400 1600 1800 2000

0

50

100

150

200

250

300

350

400

frequency (Hz)

Stratocaster FFT

Guitars

• #2-Squier Telecaster Custom– Two humbucker pickups– Two single coils with opposite polarities to

cancel the hum– Outputs a warmer and broader sound

GuitarsTelecaster Custom FFT

0 500 1000 1500 2000 2500

0

20

40

60

80

100

120

140

160

frequency (Hz)

Amplifier

• 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

Project Description

• Guitars and Amplifier

• DSP Board

• GUI

• Filter Designs

DSP Specifications

• DSP board used to convert signals from audio to digital and to create effects in digitalized format before returning signal to analog and being played.

• A/D converter – starts audio analog conversion to digitalized signal

• Effects- various effects put on the digitalized signal which starts with noise filter

• D/A converter – follows all the effects to put back in analog format

DSP Specifications

• A/D and D/A conversion shall sample at either 44,100 samples/sec or 48,000 samples/sec.

• Conversion, processing, re-conversion should take at most 1/sampling rate (real-time and recorded signals).

• Frequency ranges from 20Hz-20Khz (all human-audible frequencies).

• Typically, audio is converted to a 16-bit digital representation, so this shall be the complexity of the digital signal.

DSP Model

Project Description

• Guitars and Amplifier

• DSP Board

• GUI

• Filter Designs

GUI Specifications

• GUI designed on computer– Easier to set up in native Windows environment– Has to interface with DSP Board

• Drop down menu containing each filter• Default filter is distortion• Each filter shall have different options regarding

the filters and a check box to designate if the filter is on or off.

• Reverberation shall contain two value inputs- one for the delay order and one for the gain in the delay line.

GUI Specifications cont.

• Delay/Echo shall contain a slider and text box controlling the duration of the delay.

• Octaver contains only a check box• Volume Envelope contains a slider and

text box controlling how fast the sound reaches full potential after string is struck

• Chorus shall contain a slider and text box controlling the intensity of the effect and number of copied signals up to 4

GUI Specifications cont.

• Flanger contains a slider and text box adjusting the delay rate of the signal

• Phase shifter contains a slider and text box controlling the intensity of the phase change

GUI flowchart design

Project Description

• Guitars and Amplifier

• DSP Board

• GUI

• Filter Designs

Digital Effects

• Noise Filter

• Distortion

• Reverberation

• Delay/Echo

• Octaver

• Volume Envelope

• Chorus

• Flanger

• Phase Shifter

Noise Filter

• Only filter not User-defined

• Set to attenuate at 60 Hz from noise found in single-coil pickups

• Notch filter shall be used in order to pass all other frequencies.

• Gain set to 1 so filter does not distort incoming signal

Distortion

• Decides what amplitude limits will be and how much gain to add to the signal

• Gain amount shall boost the signal

• Amplitude limit shall clip the signal

• Values of gain shall range from 1 to 10, with 1 causing minimal clipping and 10 causing maximum clipping

Reverberation

• Magnitude response in frequency domain shall be 1 for all frequencies.

• User will decide the delay and gain block values for the filter (on scale of 1-10)

• Higher the gain value, the longer the sustain shall be

Reverb Test Filter

Scope

Gain

0.8

Discrete Impulse

Delay

z-4

R

R

z

zzH

1

)(

Reverb Filter Pole/Zero Diagram

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1Root Locus

Real Axis

Imag

inar

y A

xis

-1.5 -1 -0.5 0 0.5 1-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1Root Locus

Real Axis

Imag

inar

y A

xis

1st Order Design 4th Order Design

Reverb Test Filter Results

0 5 10 15 20 25

-0.2

0

0.2

0.4

0.6

0.8

n (samples)

Am

plitu

de

Impulse Response

Delay/Echo

• Shall determine the next occurrence of the signal played.

• Time range the user can input shall be from 50 milliseconds to 5 seconds

• 10-millisecond intervals

Octaver

• Filter shall act as a full-wave rectifier

• This will double the frequency, causing the note to sound one octave higher.

• On/Off selection will be used for this on the filter

Volume Envelope

• Allows the signal to gradually reach full value, taking out the initial attack of the notes

• Sound is similar to a note being played backwards

• Time for the signal to reach full value the user can input shall be from 10 milliseconds to 100 milliseconds at 1-millisecond intervals.

Chorus

• Allows a multiple-guitar sound

• Filter shall copy the signal and pass the copied signal through a delay from 30 to 40 ms

• User shall determine how many other signals are generated up to 4 and the rates of delay of each signal

Flanger

• Copies the signal and delays the copy by varying values less than 20 milliseconds

• The signal shall then be added back to the original signal, creating an audible sweeping effect

• The output may be fed back to create deeper • Limit of delay shall be between 5 and 15 milliseconds,

shifting 1ms every defined amount of time• Scale from 1 to 10, 1 representing delay change every 2

seconds and 10 representing delay changing every 200 milliseconds

Phase Shifter

• Signal copied, copy is modified, and the two signals are added together

• Phase is shifted on the copy rather than delaying the signal.

• This shall be created by passing the copied signal through eight cascaded all-pass filters with a feedback loop.

• User shall configure the filter by choosing the depth of the notches created in the frequency response when two signals are added.

Equipment List

• MATLAB software w/ Simulink and Signal Processing Toolbox

• Texas Instruments DSP board• Computer used in Lab• Fender Frontman 15R Guitar Amplifier• Squier Stratocaster Affinity Series Electric

Guitar• Squier Telecaster Custom Series Electric

Guitar

Schedule Of TasksWeek and Date Alex Czubak Gorav Raheja

Week 0: Winter Break 2007/2008Research of all-pass filter design, clipping signals,

frequency change Research of GUI design and programming

Week 1: January 24, 2008 Design and test of Noise Filter, Aid in GUI design Begin programming of GUI

Week 2: January 31, 2008 Design and Test Reverberation Filter Program GUI

Week 3: February,7,2008 Design and Test Distortion Filter Program GUI

Week 4: February 14, 2008 Design and Test Octaver Filter Program GUI, Aid in Octaver Filter Design

Week 5: February 21, 2008 Design Volume Envelope Filter Program GUI, Aid in Volume Envelope Filter

Week 6: February 28, 2008Continue Design of Volume Envelope and Test,

Help with GUI Program GUI

Week 7: March 6, 2008Finish Testing Volume Envelope, Design Flanger

Filter Program GUI

Week 8: March 13, 2008 Test Flanger, Begin design of Phase Shifter FilterDebug GUI, Look into design schemes for the

Chorus Filter

Week 9: Spring Break Research Phase Shifter Design Research Chorus Design

Week 10: March 27, 2008 Design and Test Phase Shifter Design Chorus Filter

Week 11: April 3, 2008 Design Delay/Echo Filter Design and Test Chorus Filter

Week 12: April 10, 2008Design and test Delay/Echo Filter, Begin Real-

time audio resting Begin Real-time audio testing

Week 13: April 17, 2008 Real-time implementation Debug GUI, Real-time audio testing

Week 14: April 24, 2008Real-time implementation, Work on presentation

and paper Work on presentation and paper

Week 15: May 1, 2008 Presentation Presentation

Bibliography"http://www.squierguitars.com - Strat (Rosewood)." Squier Guitars by

Fender. 10 Dec. 2007 <http://www.squierguitars.com/products/view_specs.php?fullpartno=0310600&name=Strat%26reg%3B+%28Rosewood%29>.

"http://www.squierguitars.com - Vintage Modified Telecaster Custom." Squier Guitars by Fender. 10 Dec. 2007 <http://www.squierguitars.com/products/view_specs.php?fullpartno=0327502&name=Vintage+Modified+Telecaster%26reg%3B+Custom>.

"http://www.fender.com - Frontman 15R." Fender.com. 10 Dec. 2007<http://www.fender.com/products//view_specs.php?fullpartno=0231501000&name=Frontman%26trade%3B+15R>.

Oboril, David, Miroslav Balik, et al. Proceedings of the COST G-6 Conference on Digital Audio Effects. “Modelling Digital Musical Effects for Signal Processors, Based on Real Effect Manifestation Analysis.” December 7-9, 2000: Verona, Italy.

BibliographyKarjalainen, Matti, Henri Penttinen and Vesa Valimaki. IEEE. “Acoustic

Sound from the Electric Guitar Using DSP Techniques.” 2000: Helsinki, Finland.

Fernandez-Cid, Pablo and Javier Casajus-Quiros. IEEE. “Multiband Approach to Digital Audio FX.” 2000: Madrid, Spain.

Verfaille, Vincent, Udo Zolzer and Daniel Arfib. IEEE Transactions on Audio, Speech, and Lauguage Processing. “Adaptive Digital Audio Effects (A-DAFx): A New Class of Sound Transformations.” Volume 14, Number 5. September 2006.

Qi, Yuting, John William Paisley and Lawrence Carin. IEEE Transactions on Audio, Speech, and Language Processing. “Music Analysis Using Hidden Markov Mixture Models.” Volume 55, Number 11. November 2007.

Keen, R.G. Guitar Effects FAQ. May 20, 2000. http://www.geofex.com/effxfaq/fxfaq.html

Bibliography

Caputi, Mauro J. IEEE. “Developing Real-Time Digital Audio Effects for Electric Guitar in an Introductory Digital Signal Processing Class.” 1998. <http://www.ewh.ieee.org/soc/es/Nov1998/01/BEGIN.HTM>

Stewart, Dr. Thomas L. Bradley University. Professor and Advisor. October 18, 2007.

"Harmony Central - Flanging." Harmony Central. 2007. 11 Dec. 2007 <http://www.harmony-central.com/Effects/Articles/Flanging/>.