Guitar Effects Generator Using DSP By: Alex Czubak Gorav 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 Stratocaster FFT 400 350 300 250 200 150 100 50 0 0 200 400 600 800 1000 1200 1400 1600 1800 2000 frequency (Hz) Guitars • #2-Squier Telecaster Custom – Two humbucker pickups – Two single coils with opposite polarities to cancel the hum – Outputs a warmer and broader sound Guitars Telecaster Custom FFT 160 140 120 100 80 60 40 20 0 0 500 1000 1500 2000 2500 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 • Flanger • Distortion • Phase Shifter • Reverberation • Delay/Echo • Octaver • Volume Envelope • Chorus 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 -4 z Discrete Delay Impulse 0.8 Gain Scope z R H ( z) 1 z R Reverb Filter Pole/Zero Diagram Root Locus 1 Root Locus 1 0.8 0.8 0.6 0.6 0.4 0.4 0.2 Imaginary Axis 0.2 Imaginary Axis 0 0 -0.2 -0.2 -0.4 -0.4 -0.6 -0.6 -0.8 -0.8 -1 -1 -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 1 Real Axis Real Axis 1st Order Design 4th Order Design Reverb Test Filter Results Impulse Response 0.8 0.6 0.4 Amplitude 0.2 0 -0.2 0 5 10 15 20 25 n (samples) 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 Tasks Week and Date Alex Czubak Gorav Raheja Research of all-pass filter design, clipping Week 0: Winter Break 2007/2008 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 Continue Design of Volume Envelope and Test, Week 6: February 28, 2008 Help with GUI Program GUI Finish Testing Volume Envelope, Design Flanger Week 7: March 6, 2008 Filter Program GUI Debug GUI, Look into design schemes for the Week 8: March 13, 2008 Test Flanger, Begin design of Phase Shifter Filter 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 Design and test Delay/Echo Filter, Begin Real- Week 12: April 10, 2008 time audio resting Begin Real-time audio testing Week 13: April 17, 2008 Real-time implementation Debug GUI, Real-time audio testing Real-time implementation, Work on presentation Week 14: April 24, 2008 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=02315 01000&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. Bibliography Karjalainen, 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/B EGIN.HTM> Stewart, Dr. Thomas L. Bradley University. Professor and Advisor. October 18, 2007. "Harmony Central - Flanging." 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