We expand on our previous guide with some more synthesis types…
In a previous article here on this blog, we covered some of the most common synthesis types: subtractive, PCM and FM.
There are more, however…
Here’s an explanation of how two less common synth types work…
Wavetable synthesis was another early digital synthesis type, this time pioneered by Wolfgang Palm withthe PPG Wave synth. In a sense, it is a forerunner to sample-based synths, but it employed digitally created single cycle waves as its source.
Previously, analogue synthesis had provided the user with a small selection of simple waveforms as oscillators (sine, square, saw etc). With the sound shaping tools offered by subtractive synthesis, this enabled a broad tonal palette to be created.
The PPG used digital technology to expand on this in a number of different ways. Firstly, used digital oscillators, and could store many different wave types.
These were stored as single cycle waveforms, and could be far more complex than analogue oscillators. Accessed via a front panel knob, the waves were read from a look-up table (wavetable). This meant that wave types could be controlled via LFOs or other controls, and stepped through, for interesting shifts in timbre.
Often sounds wavetables would be arranged in a manner that meant that harmonics increased as you moved through the wavetable, more subtle shifting effects could be achieved. Each wavetable had 64 waveforms arranged in different ways, for different effects.
Once again, the PPG employed elements of subtractive synthesis to shape its sounds- in this case analogue filters, analogue filters, LFOs etc.
For a stunning, modern take on this technology, take a look at the excellent Nord Wave synth, which has Wavetable functionality, among other synthesis types.
You might think that additive synthesis is like subtractive synthesis in reverse, and in a sense, you’d be right. You also might think that it is also fairly simple to understand, like its subtractive sibling. Well, you’d be wrong in that regard, and it is for this reason that additive synths are fairly uncommon.
The principle that underpins this type of synth is that sounds are made from a combination of harmonic and inharmonic overtones- sine waves of different frequencies. Basically, it means that combining sine waves of different frequencies can create different tones, by way of phase addition and cancellation. (Interestingly, this is also how a tonewheel, drawbar organ like a Hammond works, technically making it an additive synthesizer…)
Sounds simple, doesn’t it?
The problem is that the mathematics involved is pretty complex. Simple waves like square waves, sawtooth waves, triangle waves and pulses are created by combining different harmonic tones.
These are sine waves that have a mathematical relationship to each other. Creating a more complex tone means that you need some understanding of which harmonics will need to be used.
The other problem is that one of sheer power needed to create even simple sounds. For example, a sawtooth would be a single oscillator on a subtractive synth. Using additive synthesis, it is made by combining the fundamental frequency (the note pitch) with odd and even harmonics, however. The more harmonics are used, the better the more accurate, and richer the sawtooth.
Each of these, in a sense, corresponds to an oscillator, however, meaning that even simple sounds can place huge demands of synth resources.
As computers have ramped up in power, additive synths have become a more realistic possibility, with the added advantage of simple interfaces, too.