Electronic Music
Dr Ian Drumm
Granular Synthesis
• Aims
– An introduction to Granular Synthesis
• Learning Outcomes
– Grains as elements of sound
– Control parameters
– Applications
Basic Concept
• At t<20ms 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
Grain’s Amplitude Envelope
Attack, Sustain and Decay sections
• Three part linear
• Gaussian
1 ( t ) 2 / 2 2
A(t ) e
2
σ is standard deviation
μ is mean
• Pulse – sound like wood block taps
• Narrow envelopes – crackling and popping
Implementation
• Waveform generator X Envelope generator
• Control on a grain by grain basis makes this
technique powerful
Control Data
• Method comes into it’s 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
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
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
Cloud Shapes
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 don’t change
can be thought of as monochrome.
Transchrome and polychrome variations in cloud
give richer and dynamic sounds.
AGS: Control Parameters
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).