tags: music granular-synthesis synthesis audio composition digital mus-305 ece-402 mus-409

Granular Synthesis

Granular synthesis is a method of [synthesizing sound] that manipulates [sound] on the [microsound] level.

• like spray-painting; atomizing small portions or windows of a sound and rearranging them in new ways.
• a set of techniques for creating sound constructed from numerous individual sound grains (MUS 409)
  • extremely flexible and multi dimensional
  • no minimum and maximum to what we call a “grain”

Grain

A grain is a short sound [sample], typically 1-100 ms

• the smallest we could get is one [sample]
• lots of situations where we might have granular algorithms that stretch grains to 3-10 seconds - is it really a grain anymore?
• a gray-ish area between granular synthesis and just sampling
• often at or near the threshold of frequency/amplitude discrimination

Input signal segmented into grains, then recombined/resynthesized according to various parameters

Brief History

• Isaac Beekman, “corpuscular” theory of sound, Scientific Revolution (mid 16th-17th)
  • splattering of sound on the ear?
• Dennis Gabor, Acoustical Quanta and the Theory of Hearing (1964)
  • proposed that sound could be viewed and understood as quantum particles
  • you could make “any sound” using this particulate approach
  • Gabor constructed an optical/mechanical sound granulator (similar to [Light Tone Organ])
• Granular synthesis is a popular technique by virtue of its flexibility

Windowing

Windowing in granular synthesis is process of creating grains by applying a short [amplitude] [envelope].

• shaping the grain - the attack transients
• might be a bell curve, a percussive window function (short attack, long release), any shape under the rainbow is possible

Applications

It is a technique used in [music-composition] and production.

• invention of granular synthesis commonly attributed to Iannis Xenakis (Wikipedia)

Granular synthesis can be used both functionally and compositionally. Functionally, it can be used for time-stretching audio without changing [frequency]. Compositionally, using granular synthesis on sounds with significant [transients] (rather than sustained sounds) can create interesting gestures at the note level.

TODO: take more notes: https://www.izotope.com/en/learn/the-basics-of-granular-synthesis.html

Granular Synthesis Parameters

• waveform type - [sine wave], sampled sound, etc.
  • earliest fixed granular synthesis only worked on sine waves - there’s quite a lot you can do
• grain density/frequency - how many grains per second?
  • synchronous/asynchronous
  • synchronous = exact grains per second (grain frequency)
  • asynchronous = stochastic, random (approximate frequency)
• gap size/hop size - time between consecutive grains
  • more specifically, time between the onsets of adjacent grains
  • also called Inter-Onset Time (IOT)
• density/frequency and gap size/hop size seem to be related
  • language depends on the specific granular device
• grain duration
• grain pitch/transposition
• grain start position - from where in the original sample does the grain originate?
• grain pan (L/R)
• grain envelope/window function
  • triangle, rectangle, tukey, sine, percussive, reverse percussive

Duration/Spectrum Relationship

TODO: create separate note

• There is an inverse relationship between duration & spectrum bandwidth
• infinitely short sound (impulse) → infinitely wide spectrum
  • impulse response?
• likewise, longer TD events → narrower FD spectra:
  • distinct spectral peaks, esp. for sine waves and other simple waveforms
• unit impulse
• long vs. short grain window
  • granulated 500 Hz sine wave, 100 ms grain duration (pure frequency with a little spectrum widening)
  • granulated 500 Hz sine wave, 1 ms grain duration (wide, crackling broadband noise)
• consequences:
  • short grains → broader, noisier spectrum
  • sharp transients in grain window → similar effect
    • crackling, popping, glitchy texture
• longer grain duration → narrower spectrum, fewer frequency, “smoother” sound

Sources

• MUS 305 Lecture
• https://en.wikipedia.org/wiki/Granular_synthesis