4. Synthesis Fundamentals

Computer Music
: Synthesis, Composition, and Performance

Charles Dodge & Thomas A. Jerse

4. Synthesis Fundamentals

4.1 Computer Instruments, Unit Generators, and Sound-Synthesis Techniques


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In computer music, the term instrument refers to an algorithm that realizes (performs) a musical event. It is called upon by a computer program that is interpreting either a score stored in memory or the actions of a performer on a transducer. The instrument algorithm calculates the sample values ot an audio signal  using inputs, known as  parameters, received from the calling program. (...) When designing an instrument, the musician determines the number and nature of the parameters to be passed. These are based on a choice of which attributes of the sound will be controlled externally during the generation of the sound. An instrumental can also be designed to accept an audio signal in digital form as an input to be processed by the algorithm.


The ways to specify and provide control of computer instruments

(1) step-by-step program to generate sample values (at the lowest level)

(2) dividing a complete sound-generating algorithm into smaller, separate algorithms called unit generators (to improve both conceptual clarity and programming convenience)

(3) With signal-generating models, the musician chooses from a set of available synthesis techniques.
- synthesis-from-analysus techniques: additive synthesis & subtractive synthesis,
- distortion synthesis: frequency modulation (: distortion of the frequency of a tone) & waveshaping(: distortion of the waveform of a tone): Granular synthesis

(4) physical model


4.2 Signal Flowcharts

A signal flowchart is a graphical representation of the way in which unit generators are interconnected to form an instrument.

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The interconnection of unit generators
(1) An output can drive more than one input.
(2) Outputs may never be connected directly together.

Outputs can be combined by mathematical operations.
- adder: mix signals together
- subtracter
- multiplier: amplification
- divider: attenuation


4.3 The Oscillator

The unit generator fundamental to almost all computer sound synthesis is the oscillator. An oscillator generates a periodic waveform.

fig 4.2 flowchart symbol for an oscillator

ref.
http://en.wikipedia.org/wiki/Signal_generator