Stacking is an arrangement technique that is often interchanged with the term layering. However, there is a distinction – at least for the purposes of this article. Stacking produces a composite sound made up of similar timbres. Additionally, the timbres are often transposed and detuned, yet they all contribute to one wholesome sound.
Layering highlights the independent character of timbres – it is less about making a single sound and more about making an evolving, dynamic unison. This diagram from Chapter 7 of the Sound Synthesis and Sampling book by Martin Russ lays out this distinction nicely.
These techniques were first implemented using keyboard hardware featuring multi-timbral, split, and unison modes. Of course, you can simulate this technique by simply duplicating software synths. However, in this implementation, the stack is not playable.
DIFFERENCE BETWEEN POLYPHONY AND MUILTITIMBRALITY
The concept of stacking and multiple timbres should not be confused with polyphony. Polyphony answers “How many different keys can I play at the same time?” while multitimbrality answers “How many sounds can I trigger with one key?”
A combination of different sounds happening at once. However, it is best to use just 2 or 3. There are three types of composites.
Additive – Use simple sounds like sine waves and filtered complex waves. By keeping the sounds simple, you have more room in the mix to add timbres without over-complicating the sound. (See Blog: Methodical Synthesis)
Hybrid – Sounds consist of contrasting yet complementary sounds. For example, you might combine an FM sound with an Additive sound because FM is usually inharmonic and additive is usually harmonic. You might combine a familiar sound like a violin with an alien sound like a modulated wavetable, or an analog sound with a digital sound. (See Blog: Methodical Synthesis)
Splitting – The process of breaking one complex sound into multiple simpler sounds, treating them individually, and processing them again together. This technique may merit the use of spectrum analyzers, noise gates, and bandpass filters. The first example below is my complex source. The second example is my split stack.
METHODS OF DOUBLING
Describes the re-use of some musical information. Doubled sounds are typically the same timbre, but transposed or tuned to different pitches before being played together. This means each note movement will produce a parallel interval. (See Blog: Scales, Intervals).
Detuning – Introduces chorusing and beat frequencies (See Blog: Modulation FX). In order to preserve the center pitch, be sure to detune each component either the same amount in different directions or detune just one.
Octaving – Transpose components by an octave(s). This technique can really thicken up the sound, but it also gives the components more independence than other techniques do. Octaving on certain scale degrees can alter the overall weight of the harmony – so be careful.
Intervals – Transpose components by intervals other than the octave. However, it induces parallel chord motion and potentially throws off the harmony.
Chording – Transpose 2 parts away from the central part, creating a chord. This technique is more experimental but has the highest potential for throwing off the overall harmony.