1. Developing a Versatile Audio Synthesizer TJHSST Computer Systems Lab
Victor Shepardson
Developing a Versatile Audio Synthesizer
TJHSST Computer Systems Lab

2. Sound and its Digital Representation22
Sound and its Digital Representation
Waveforms:
Pulse Code Modulation:
signal amplitude at regular intervals represented by a binary integer

3. Methods of Synthesis -Subtractive -Sampling -Additive -FM33
Methods of Synthesis
-Subtractive
-Early analog machines
-Oscillator and filter stages
-Sampling
-Very effective at imitation
-Light on processing
-Memory needed for samples
-Additive
-FM

4. Additive Synthesis -Fourier -Summing Oscillators -Fourier Transforms44
Additive Synthesis
-Fourier
-Periodic functions can be decomposed to spectra:
Amplitude, frequency and phase of sine waves
-Summing Oscillators
-Fourier Transforms

5. FM Synthesis -Frequency Modulation:55
FM Synthesis
-Frequency Modulation:
-One audio band signal modulates another
-Analog: hard
-Digital: easy
-Digital Oscillators
-Powerful Controls:
-M:C ratio
-Modulation Index

6. Cross Coupled Oscillators66
Cross Coupled Oscillators
-The output of each oscillator is coupled to an input of another
-Convergent/divergent spectra
-Buzzing, hissing “natural” sonorities

7. Synthesizer Elements -Time Functions -Mixing Blocks77
Synthesizer Elements
-Time Functions -Mixing Blocks
-Digital Oscillators -Notation Objects

8. Frequency/Amplitude Functions88
Frequency/Amplitude Functions
And Mixers
Functions:
No input, output a floating point
Constant or time dependent
-Mixers:
Operate on inputs based on control signal
Freq
OUT
Control
OUT
IN1 CTRL
Mix (+)
OUT

9. Oscillators -Frequency and Amplitude inputs -Has a waveform99
Oscillators
-Frequency and Amplitude inputs
-Has a waveform
-At each time step, computes the next value based on waveform and momentary frequency
Freq
OUT
Amp
OUT
FREQ AMP
Oscillator
(sine)
OUTPUT

10. Notes and Note Sequences
Notes and Note Sequences
-Note objects contain information about pitch, duration, and envelope shape
-Note sequences are lists of note objects
-can be generated from strings of notation
-can, in turn, generate corresponding freq/amp functions

11. Implementing Additive Synthesis
Implementing Additive Synthesis

12.
Implementing FM

13.
More Complex FM

14.
References
Chowning, J., "The Synthesis of Complex Audio Spectra by Means of Frequency Modulation". Journal of the Audio Engineering Society 21(7), pp , 1973.
Moore, R., Elements of Computer Music, Prentice Hall, Englewood Cliffs, NJ, 1990.
Valsamakis, N. and Miranda, E. R., "Iterative sound synthesis by means of cross-coupled digital oscillators", Digital Creativity 16(2), pp , 2005.