ECE4803B: Theory and Design of Music Synthesizers

Instructor: Prof.
Aaron Lanterman
Office: Centergy 5212 (often) or Bunger-Henry 323 (rarely)
Phone: 404-385-2548
E-mail:
lanterma@ece.gatech.edu
Course website: users.ece.gatech.edu/~lanterma/ece4803

When and where: MW, 4:30-6:00, Van Leer C457 (sent via real-time
video link to GTREP)

The photo: Aaron in the beginning stages of putting together
the MOTM-485
VCF, which is based on the diode-ring Sallen-Key filter from
the
Yamaha
GX-1 (in case you’re wondering, the answer is yes, I am the only prof on
my floor with a soldering iron!)

 

Aaron’s SDIY Pages

• Synth
  DIY Datasheet and Ap Note Collection
• Music synthesis
  patents collection, with some brief commentary
• Current
  modular synth manufacturers – look through these to get ideas for your
  own new designs, ideas for packaging, etc.

Homeworks

• Homework 1 (due 1/30)
• Homework 2 (due 2/8)
• Homework 3,
  Solutions (originaly due 2/22,
  but extended to 5 PM – can slip under my Bunger Henry 323 office door –
  I’ll come grab them before heading out for the weekend)
• Homework 4 ,
  Solutions (due 4/1)
• Homework 5,
  Solutions (due 3/15)
• Homework 6 ,
  Solutions (due 4/1)

Lectures

Lectures may be downloaded as
RealPlayer
files. Warning: They’re pretty big (150 to 200 MB). If you find these
lectures useful, please consider making a small donation (maybe $25 or
thereabouts, although any amount is appreciated)
to the Georgia Tech Foundation earmarked to go towards
my synthesizer research; the funds will go towards parts and equipment
for student projects.
Here
are instructions on how to donate.

• 1/9 –
  40 Years of Music Synthesis, Part I (Moog/Buchla up to DX7)
• 1/11 – 40 years of Music Synthesis, Part II
  (DX7 and after)
• 1/18 –
  Meet the Korg MS-20, a typical analog semimodular synth
• 1/23 –
  Op amp review, part I (resistive circuits)
• 1/25 –
  Overview of Music Technology Projects – guest lecture by
  Gil Weinberg
• 1/30 –
  Op amp review, part II (first-order RC circuits)
• 2/1 –
  Operational Transconductance Amplifiers (OTA)
  (with VCA example), Norton
  op amps
• 2/6 –
  Voltage Controlled Oscillators (VCO): Sawtooth Core;
  visit to
  the ECE4006 labs
• 2/8 –
  Voltage
  Controlled Oscillators (VCO): Triangle Core; distribution
  of the MOTM kits
• 2/13 –
  Analog Waveshaping, Part I: saw->pulse, saw->triangle,
  triangle->sine, Serge wave multiplier demo
  Suggested references:
  • R. Williams,
    Triangle to Sine Conversion with OTAs
  • M.H. Miller,
    “Triangle
    to Sine Conversion (Nonlinear
    Function Fitting)”, ECE414 Notes
  • R.G. Meyer, W.M.C. Sansen, S. Lui, S. Peeters,
    
    “The Differential Pair as a Triangle-Sine Wave Converter”,
    IEEE J. of
    Solid-State Circuits, June 1976, pp. 418-420.
  • G. Klein,
    Accurate Triangle-Sine Converter
  • Far-out ideas:
    • H. Hassan, FET
      Differential Amplifier as a Tri-Wave to Sine Converter,
      Proc. 36th Southeastern Symposium on System Theory, 2004, pp. 427-430
    • Z. Tang, O. Ishizuka, H. Matsumoto,
      MOS Triangle-to-Sine Wave Convertor Based on
      Subthreshold Operation, Electronics Letters,
      Vo. 26, No. 23, Nov. 8, 1990, pp. 1983-1985.
• 2/15 –
  Analog Waveshaping, Part II: Ken Stone’s wavefolder,
  Buchla’s diodeless deadband circuit, Buchla’s timbre generator
• 2/20 –
  Single-pole OTA-based VCFs (and MOTM kit progress)
• 2/22 –
  Four-pole VCFs with negative feedback
• 2/27 –
  Properties of Second-order filters
• 3/1 –
  Sallen-Key VCF theory; Buchla LPG example (Vactrol-based S-K)
• 3/13 –
  Sallen-Key
  OTA-based examples; State-variable filter theory
  (show & tell of assembled MOTM kits)
• 3/15 –
  State-variable VCF examples
• 3/27 –
  Transistor Ladder (Moog) and Diode Ladder VCFs, and a few other odds
  and ends
• 3/29 –
  Exponential voltage-to-current conversion
• 4/3 –
  Sample playback and the dangers of aliased digital oscillators
• 4/5 –
  Alias-free synthesis of classic analog waveforms; digital state
  variable filters (At some point, I say “I don’t know why you need a delay
  here.” I have no idea why I said that… clearly you need a delay when you
  code it up. I said some nonsense about stability – that’s not the issue.
  Ignore anything I say that’s nonsense.) (First part of the lecture was devoted
  to ads for some student activities, so you can skip ahead.)
• 4/12 –
  Digital emulation of a SSM2040/Prophet 5-style filter
  (You can ignore anything after where I say “let’s try
  matching the half-power point,” or something like that; I ran out of note
  material and tried to freewheel it, and spun off into oblivion.
  I was also just generally brain dead that day…)
• 4/17 – Impulse invariance techniques
  (alas, this appears to not have been taped…
  sorry…)
• 4/19 –
  Demo of SSM2040/Prophet 5-style emulation VCF;
  Waveshaping and Chebychev Polynomials
• 4/24 –
  Additive Synthesis
• 4/26 – FM Synthesis

References

We will draw material from numerous sources: book, articles, patents,
and particularly schematics and descriptions posted on websites. Think of
google as the main class text.

So far, I’ve drawn material from the following books (which I’d recommend
getting if you want to pursue the topic beyond this course):

• Hal Chamberlin, Musical Applications of Microprocessors, 2nd
  Edition, Hayden, 1982; if you
  get just one book, this is THE book to get. Although it has
  “microprocessors” in the title, it has a superb section on analog circuits.
  NOS (New Old Stock – meaning old, but unused) copies are available for
  purchase from Jeff Dec ($50 + shipping); e-mail
  jdec@mindspring.com
• Barry Klein, Electronic Music Circuits, SAM, 1982. Long out
  of print, but photocopies can be purchased directly from
  barry.l.klein@wdc.com

Highly Tentative Outline

• Intro: 40 Years of Music Synthesizers
• Overview of a typical “modular” synthesizer
  • Control voltage concept; gates and triggers; signal standards
  • MS-20 demo
  • Reaktor demo
• Voltage Controlled Oscillators (VCO)
  • Saw and Triangle Cores
  • V-to-I Exponential Conversion
  • Basic waveshaping: saw->tri recitification, tri->sin warping
• Digital oscillators
  • Sample recording and playback; constant vs. variable D/A clock rates
  • Wavetables
  • The evils of aliasing
  • Band-limited impulse trains
• Complex analog waveshaping circuits
  • Deadband addition (Don Buchla style)
  • Wavefolder cascade (Serge style)
• Digital waveshaping
  • The evils of aliasing
  • Chebychev polynomials
• Voltage Controlled Filters (VCF)
  • Analog filter topologies
    • Four-pole buffered with negative feedback
    • Four-pole unbuffered with negative feedback
    • State Variable
    • Sallen-Key
  • Variable gain/resistance techniques
    • Vactrols
    • Operational transconductance amplifiers
    • Dynamic diode resistance
  • The Moog transistor ladder filter
• Digital emulations of analog filters
• Additive synthesis
  • Analysis/resynthesis
• Frequency Modulation (FM)/Phase Modulation (PM) synthesis
• Physical modeling synthesis
  • The wave equation
  • Travelling wave solutions and waveguides
  • Excitation models: plucking, blowing, stick/slip bowing