MATRIXSYNTH: Synthesis 101

Synthesis 101

This page was created as a background piece for my M-Audio Venom review. I won't go into full detail on all synthesis methods here as that would be virtually endless. The following is just meant to give you some background so you can get a basic understanding of where the Venom fits with other synthesizers and for those new to the internals of sound design.

At the most basic level you can think of a synthesizer as a synthetic sound source that can be manipulated and processed to produce various sounds over time. The whole is the synthesizer, but for now we will focus on the raw sound source component of a synthesizer typically referred to as the oscillator. The most commonly known methods of synthetic sound sources in hardware synths are analog, virtual analog, sample/PCM, FM, Additive and Wavetable. There are others like granular synthesis on the Access Virus, but we'll focus on the more common and those relative to the Venom. Also worth noting is the Venom is capable of Formant type sounds. Formant synthesis allows you to create vocal-like synthetic sounds. It can be done at the oscillator level like on Yamaha's FS1R or it can be done with filters. On the Venom it's done with filters. See Taiho's Tips and Tricks at the end of this post for details.

Analog oscillators are typically capable of producing an initial set of limited waveforms, for example, standard sine, saw and pulse waves. These can sometimes be further modulated to produce other waveforms. Virtual analog is the same but modeled in software.

Sample or commonly known PCM based sound sources are exactly that, samples of sounds in various lengths depending on the synthesizer. Samplers fall into this bucket as well.

FM originated by John M. Chowning (https://secure.wikimedia.org/wikipedia/en/wiki/John_Chowning) in 1967 and later made famous by Yamaha with the DX7 and subsequent synths, uses various combinations of oscillators to modulate each other to produce various timbres.

Additive synthesis uses multiple harmonics or non-harmonics to add to the sound source. You can adjust the frequency and amplitude of each to create different sources of sound. The most common use of this technique is the drawbar organ. You add or remove harmonics with the drawbars. You can also think of an additive synth like a giant EQ on steroids where not only can you bring harmonics in and out but you can do the same for other aspects of each harmonic. Synths that use the technique are relatively rare and include the RMI Harmonic synthesizer, DK Synergy, and the more current Kawai K5 and K5000 synths.

Wavetable synthesis is technically sample-based in source, but very different. Instead of a prolonged sample of say a violin, wavetables typically consist of a table of single cycle waveforms - think individual snapshots of waveforms viewed in an oscilloscope. This would be closer in essence to an analog oscillator's waveform vs. a recording of an instrument to be played back. For example, on an analog synth if you output a pulse wave to an oscilloscope, you'd see what looks like squares or rectangles depending on its width, and for a saw, you'd see ramps similar to a physical saw blade. The single cycle waveforms in wavetable synthesizers are like this but instead of the standard analog waveforms, they are digital snapshots of far more varied waveforms. The PPG line of wavetable synthesizers followed by Waldorf and the one-off Ensoniq Fizmo used this technique. What makes a wavetable synthesizer so interesting is the "table" in wavetable. To visualize a wavetable, picture a standard spreadsheet where every cell in that spreadsheet has a different single-cycle waveform. You can select a given wave in the table as your oscillator source or you can do something a bit more interesting. You can sweep through the table so that the waveform heard changes over time. That's where the magic comes in. You do this by assigning a modulation source like an LFO, envelope or pressure aftertouch to the wave position. Typically you can also set the range of the table you want to sweep.

The above covers the most common sources of raw audio in most synthesizers. I won't go into as much detail with the remaining components of synthesis as I'm guessing most of you are very familiar with them, but in short you have your sound source and it follows a path until it is output. That path typically goes something like this: oscillator --> mixer --> filter --> amplifier --> effects (if the synth has them) --> output. Along the way you can typically apply modulations to each step. The most common modulation sources include envelopes and LFOs. Envelopes allow you to shape the length of a sound when you press a key or when you trigger a sound via a sequencer or other. The envelope determines whether what you hear sounds like a plucked or percussive instrument or a like a bowed string instrument. You typically set what happens over time by adjusting the time of four stages - Attack, Decay, Sustain, and Release. You can also use envelopes to modulate other things like filter cutoff and resonance, pitch, LFO rates, and so on. LFOs let you produce a cycling effect over time. Some synths have set modulation sources and destinations and some allow you to freely mix and match sources to destinations similar to patching a modular synth. Some other sources include keyboard aftertouch, keyboard velocity, the range of the keyboard and so on. The Venom's fixed modulation settings and freely assignable Mod Matrix are covered below.

The following touches on the overlap between subtractive, additive, analog and digital synthesis. Subtractive synthesis by definition is the process of starting with a raw source sound and removing harmonics of that sound; additive synthesis by definition is the process of starting with no sound and adding harmonics to create sound. Analog and digital refer to the technology used for the various components of a synth - oscillators, filters, LFOs, envelopes, etc can be either purely digital, purely analog or digitally controlled analog. Virtual analog is digital emulation of analog in software. If you think about it and separate the source of the sound from the remainder of the synth, conceptually there is overlap between subtractive and additive synthesis. For example, the Kawai K5000s is an additive synthesizer that follows the typical subtractive synthesis path with filters. The additive portion of the synth is the additive sound source section, the subtractive is the filter. Yamaha's DX200 uses FM synthesis with a subtractive filter. The Waldorf XT is a subtractive wavetable synth. Back to the review.

See this post on Vector and Wavetable synthesis.
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