Making Virtual Electric Guitars and Guitar Effects Using Faust and Octave

[Note: This appendix is newly under development for the 2008 edition of Physical Audio Signal Processing, and it therefore does not appear in the 2007 hardcopy edition. Most of this appendix is included in the RealSimple module [461], where a PDF version and associated downloadable software may be obtained.]

This appendix describes use of the Faust programming language^D.1by Yann Orlarey [344,171] to generate real-time DSP plugins from a high-level specification. An introductory tutorial appears in Appendix K of [460].^D.2The goal of this appendix is to present a series of working examples ranging from the simplest cases to richly responsive virtual instruments. It so happens that proceeding in historical order serves this goal quite well, at least initially. Another advantage of historical order is that there are no known patents on the synthesis techniques described. In summary, the focus of this appendix is to present and discuss software implementations of virtual electric guitars and associated effects, introduced in historical order initially followed by a special related topics.

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Subsections

• Karplus-Strong Digitar Algorithm
  • Exciting the Digitar String
  • MIDI Control of the KS Digitar in PD
  
  
• Extended Karplus-Strong Algorithm
  • Pick-Direction Lowpass Filter
  • Pick-Position Comb Filter
  • One-Zero String Damping Filter
  • Two-Zero String Damping Filter
  • Dynamic Level Lowpass Filter
    • Design 1: Impulse Invariant Method
    • Design 2: Bilinear Transform Method
    • Faust Implementation
  • Tuning the EKS String
    • Tuning by Linear Interpolation
    • Tuning by Allpass Interpolation
    • Tuning by Lagrange Interpolation
  • Adding String Stiffness
  • EKS Faust Listing
  • MIDI Control of an EKS Patch in PD
  • Generality of the EKS Algorithm
  
  
• Distortion and Amplifier Feedback
  • Cubic Nonlinear Distortion
    • Faust Implementation
  • Amplifier Feedback
  
  
• Segue to the Present
• Multiband Distortion
• Coupled Strings in Faust
• Tone Controls
• Speaker and Cabinet Modeling
  • Modeling a Twelve-Inch Guitar Speaker
  • Modeling Low-Frequency Loudspeaker Roll-Off
    • Faust Implementation
  • Modeling High-Frequency Loudspeaker Roll-Off
  
  
• Pickup Modeling
  • Generalized Pickup/Pick-Position Modeling
  
  
• Modeling a Pick
• Adding a Wah Pedal
  • Digitizing the CryBaby
    • Choice of Wah Filter Structure
    • Measuring the CryBaby Frequency Response
    • Notes regarding the matlab script in Fig.D.21:
    • Notes regarding invfreqsmethod listing in Fig.D.22:
    • The Digital CryBaby in Faust
    • Conclusions Regarding the Digital CryBaby
  • Wah Pedal Based on the Moog VCF
    • Faust Implementation
  • A 2D Male Vowel Pedal
  • Special Case: A ``YoYo'' Pedal
  • Special Case: An ``All Vowels'' Pedal
  
  
• Appendix A: Known Patents

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written by Julius Orion Smith III
Julius Smith's background is in electrical engineering (BS Rice 1975, PhD Stanford 1983). He is presently Professor of Music and Associate Professor (by courtesy) of Electrical Engineering at Stanford's Center for Computer Research in Music and Acoustics (CCRMA), teaching courses and pursuing research related to signal processing applied to music and audio systems. See http://ccrma.stanford.edu/~jos/ for details.