While at college, I found a lot of interesting information about digital synthesis, so that’s where my inspiration for this article comes from. So far we’ve looked at ‘standard’ analogue approaches to sound synthesis, as well as a bit of FM synthesis because everybody likes a bit of DX7 ‘E-Piano’ now and then, and now we are going to continue that theme by focusing a little on different kinds of digital synthesis.
Overview Of Digital Synthesis
Digital synthesis is based somewhat (perhaps a little too much) on the concept of trying to emulate analogue/acoustic sounds, using different methods and techniques depending on the accuracy of the audible reproduction. Because these new methods of synthesis are computer-based, there are always limitations to what can be practically performed.
The four important methods used in digital sound synthesis are as follows:
‘Loose modeling’ consists of little or no real attempt to model sound. It is used to perform AM, FM, Walsh, and Wavetable synthesis.
‘Time-based modeling’ models sound in the time domain. It is used is granular synthesis, waveset distortion, and waveform composition.
‘Spectral modeling’ models sound in the frequency domain. It is used in additive synthesis, and re-synthesis (such as the Hartmann Neuron synthesizer).
‘Physical modeling’ uses mathematical models of acoustical properties of instruments/components. It is used to create extremely accurate reproductions of physical sounds, such as mass & spring simulations, and ‘Karplus Strong’ synthesis – to create accurate sounding ‘plucked’ sounds.
These four methods can still use analogue components within their signal chain, but are digitally-based. In addition to this, different digital synthesis techniques exist, such as the previously mentioned ‘Digital FM’ synthesis, which is neither strictly digital nor analogue, and allows for more flexibility in terms of ‘complex’ modulation. FM synthesis tries (but fails to an extent) to be like analogue subtractive synthesis, by using Yamaha’s ‘operator’ concept, as well as LFO-like modulation. ‘Walsh’ synthesis is completely digital, and uses many square waveforms to create new waveforms. Unfortunately, it’s hard to predict the frequency spectrum that will be created through this technique. ‘Wavetable’ synthesis has been made popular by famous synths such as the ‘PPG Wave’ and Waldorf’s ‘Microwave’ series. It consists of using fragments of sampled sounds which are played back and looped like a sampler. To make life easier, standard features such as envelopes, filters, and LFOs are used.