Granular synthesis is another sound synthesis technique which operates on the microsound time scale. It is the fundamental theory behind pitch-shifting and time-stretching, as seen utilised in Auto-Tune, Melodyne, and Ableton Live's warping functionality. Let's take a look at how this technique works, and how it can also be creatively used to generate extraordinary evolving soundscapes.
OVERVIEW
Granular synthesis is quite similar in concept to sampling, however the samples are not played back in a conventional manor. It involves the process of breaking up these sound samples into 'grains', which can then be redistributed or reorganised into a sequence of grains, called a 'graintable' (Price, 2005). Ultimately a grain is a tiny piece of sonic data, known as a 'microsound', generally between 10 to 100 milliseconds in length (Roads, 2004). Each grain is comprised of the sonic content and its controlling envelope. The sonic content can be derived from any source: such as an audio sample, or simply a sine wave. The envelope is then used to shape the grain, whilst also preventing any distortion at its beginning or end (Opie, 2019). A detailed SOS article describes the process more practically below:
If the software made up a graintable which played back all the grains extracted from a given sample in their original sequence and at the original speed, then you'd hear the original sample reproduced. If the software played the sequence back more slowly, gaps would appear between the slices, so the current slice in the graintable is usually looped. Played back more quickly, each grain overlaps with the next one, or some grains get skipped depending on how the software works. To avoid clicks and glitches, each grain is faded in and out with a volume envelope, a process known as 'smoothing'. (Price, 2005)
Below is an example of granular synthesis. Note how the grains are initially distinct, before blending together to generate an entirely new timbre:
Interestingly, in the analogue days, the same effect could be achieved by literally cutting the magnetic tape reel with a blade into tiny sections, and reorganising it with sticky tape and a lot of time (Roads, 1988). However, with the exponential increase in computing power, it is now possible to recreate the effect digitally; much more accurately, and with much more versatility.
PRACTICAL USES
As explained above, manipulating the graintable is the basic principle of granular synthesis. But doing so in a variety of ways enables a variety of outcomes. Mantione (2017) describes three common approaches to granulation:
Replication: where a grain is extracted and repeated
Reordering: where grains are extracted and reordered
Merging: where grains are extracted from multiple sources and combined
Replication is the underlying process that Ableton Live uses for its warp function. When an audio clip is slowed down, the grains are spread out. With the assistance of complex algorithms, the resulting gaps can then be filled by replicating adjacent grains. This has the effect of stretching the clip, without affecting its pitch (as it usually would when stretching a sample).
Merging and reordering however, is much more synonymous with sound synthesis, and is what most people would generally associate with granular synthesis. Multiple grains can be layered on top of each other, and played at different speeds, phases, or levels (amongst other parameters, depending on choice of software) as desired. At low speeds of playback, the resulting sound is quite unique, often described as a 'cloud'. At high speeds, the result is heard as a note (or notes) of novel timbre. By varying the waveform, envelope, duration, spatial position, and density of the grains, many different sounds can be produced.
In contrast, rather than using replication to maintain a clip's pitch, it can alternatively be used to alter it; as is the case for Auto-Tune. This technique employs a much more complicated algorithm, involving FFT (Fast Fourier Transform). Essentially it deconstructs a complex signal into its constituent frequencies, and uses grains to manipulate the resulting waveform until the desired pitch is reached (IOP, 2012; HyperPhysics, 2015). Though practically it is extremely difficult to alter sharp transients; such as percussive hits, and some consonants such as "t" or "d". Currently, Melodyne is arguably the most advanced package for editing audio with granular synthesis, capable of both pitch-shifting and time-stretching (amongst other features), whilst catering for transients in a sophisticated way (Price, 2005).
To give you an idea of the potential of granular synthesis (combined with some previously learned knowledge of modular synthesis), below is a sample of what can be created using Clouds. This Eurorack module is a granular audio processor by Mutable Instruments. By combining the possibilities of granular synthesis with analogue modulation (note the patches to modulate the voltage, size, and freeze functions), surreal soundscapes can be created:
Granular synthesis is an extremely versatile technique that can be used for a variety of purposes. Conventionally, it can assist with pitch-shifting, amplitude modulation, and time stretching. Sonically, it can be used to create sound effects, design material for further processing, or even to produce complete musical works in their own right. More experimentally, using stereo or multichannel scattering and random reordering, it can create dynamic, organic, and unique sounds that often have an untamed quality and can produce unexpected treats that turn into song ideas. Price (2005) even commented that if you produce ambient or film music, a decent granular synth can do half your job for you ;)
Stay Tuned
- TA
REFERENCES
HyperPhysics. (2015). Fast fourier transforms. Retrieved from http://hyperphysics.phy-astr.gsu.edu/hbase/Math/fft.html
Institute of Physics. (2012). How does auto-tune pitch correction work? Retrieved from http://www.physics.org/article-questions.asp?id=75
Mantione, P. (2017). Introduction to granular synthesis. Retrieved from https://theproaudiofiles.com/granular-synthesis/
Opie, T. (2019). What is granular synthesis? Retrieved from https://granularsynthesis.com/guide.php
Price, S. (2005). Granular synthesis. Retrieved from https://www.soundonsound.com/techniques/granular-synthesis
Roads, C. (1988). Introduction to granular synthesis. Computer Music Journal, 12(2),11-13.
Roads, C. (2004). Microsound. Cambridge, MA: MIT press.
YouTube. (2015). Eurorack - Mutable Instruments Clouds. Retrieved from https://www.youtube.com/watch?v=zLj-YBy4Aa4
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