Electronic Music

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Electronic Music

• Dr Ian Drumm

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Granular Synthesis

• Aims
• An introduction to Granular Synthesis
• Learning Outcomes
• Grains as elements of sound
• Control parameters
• Applications

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Basic Concept

• At tlt20ms we would not perceive successive tone
  bursts as single events
• Ideal suggests sound composed of successive
  elements of sound grains
• A grain is in effect a shaped tone bust
• More complex sounds from lots and lots of grains

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Grains Amplitude Envelope

• Attack, Sustain and Decay sections
• Three part linear
• Gaussian
• Pulse sound like wood block taps
• Narrow envelopes crackling and popping

s is standard deviation µ is mean
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Implementation

• Waveform generator X Envelope generator
• Control on a grain by grain basis makes this
  technique powerful

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Control Data

• Method comes into its own if grains vary on a
  grain by grain basis
• Individual grain parameters we might want to vary
  include
• duration
• envelope type
• amplitude
• frequency
• waveform type
• If the waveform is synthetic you will need at
  least an extra parameter for index into a look
  table
• If the waveform is a sample you might want to
  specify start position in the sample and the
  wavefile it is taken from
• High grain densities give an explosion in the
  number of control parameters required

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Sophisticated implementation

• Need automatic high level scheme
• Specify a few global parameters
• e.g. change of spectrum with time hence system
  takes care of generating all the different grains
  for us
• Several such high level schemes suggested that
  tend to allow experiment/artistic control rather
  that analytical/scientific control

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Example of a high level scheme

• AGS (Asynchronous granular synthesis)
• Sound produced described by the pattern of
  granules on the time/frequency plain.
• Patterns described as clouds.
• (cumulus, stratus, etc).
• Cloud parameters include
• Start time and duration
• Bandwidth
• Grain Density
• Amplitude envelope
• Spatial distribution of grains within the cloud

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Cloud Shapes
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Macroscopically varying grain parameters within
the cloud

• Grain duration shorter grain durations have
  higher bandwidths resultant sonic textures
  perceived as crackling long grain durations
  give smoother sounds. An AGS system will let you
  vary durations via mathematical functions that
  can be dependant on random numbers or time,
  frequency, etc.
• Grain waveform waveforms that dont change can
  be thought of as monochrome. Transchrome and
  polychrome variations in cloud give richer and
  dynamic sounds.

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AGS Control Parameters
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Advantages / Disadvantages

• Basic concept attractive (but not quite correct)
• Not suited to having an analysis stage (because
  not generally true acoustic theory)
• Therefore not a good emulative technique for
  classic musical timbres
• Excels at some natural sounds difficult to
  produce with other methods (e.g. crackling fire,
  water gurgling, wind gusts, explosions).