All posts tagged “Thor”
So, we finally come to the sixth and final oscillator in Thor’s armoury of sound generators. This is the wavetable oscillator that first appeared in general use in the PPG Wave Computers, and shortly thereafter in the PPG 2.x series. Like other digital oscillators, this is an often misunderstood beastie, so let’s first discuss what a wavetable actually is.
There have been a number of different uses of the word wavetable in recent years, and some of them are rather misleading. For example, I have seen texts that use the name to describe a ROM that holds a selection of unrelated PCM samples such as clarinets, electric guitars, bouzoukis and Mongolian nose flutes. There are lots of waves in the ROM and these are accessed using a lookup table, so the ROM must be a wavetable, right? Wrong!
More justifiably, academics use the word to describe the sequence of numbers that represent a single cycle of a regular, periodic waveform. One can then talk about replaying one such “wavetable” (say, a digital representation of a sine wave) or a second (say, a digital representation of a sawtooth wave).
But this is still not the definition used by most people who talk about wavetable synthesis. So let’s be explicit. For our purposes, a wavetable is not a single wave, it is a selection of (usually related) single-cycle waveforms or their harmonic representations stored digitally and sequentially in such as way that that a sound designer can create musically pleasing timbres by stepping though them while a note is being played.
Unfortunately, while the principle makes sense, this would not sound very pleasant. Imagine a ROM containing just two waveforms: the aforementioned sine and sawtooth waves. Now imagine hearing a sound comprising a few cycles of the sine wave followed by a few cycles of the sawtooth wave, followed by a few cycles of the sine wave followed by the few cycles of a sawtooth wave… and so on. The resulting waveform would exhibit discontinuities each time that one waveform replaced the other, and you would therefore hear a succession of clicks polluting the sound. Consequently, a wavetable synthesiser has to be a bit cleverer than that, providing a mechanism for morphing from one wave to the next. Instead of swapping instantly from the sine wave to the sawtooth wave, there would be a transition period during which the waveform changed smoothly from one extreme (the sine wave) to the other (the sawtooth wave) and back again.
“More than just DX pianos”
In the last tutorial, I introduced the concept of FM algorithms, the ways in which FM operators can be connected together to create sounds. A Thor FM Pair Osc comprises two operators – a modulator that is permanently connected to the FM input of a carrier – and we can represent this as shown in figure 1.
Of course, Thor has three oscillator slots, and you can place an FM Pair in each of these so, by default, the standard algorithm offered by Thor is as shown in figure 2: three pairs that can be mixed together, but which don’t – for the moment – interact in any other way. There are many uses for this algorithm, which can be used to create very interesting string ensemble and organ patches, among others. But I fancy stepping beyond these, so I’m going to demonstrate this algorithm by showing you how to create an evolving pad that has a rich, analogue flavour.
Frequency Modulation (FM) has become the bogeyman of synthesis. Whereas, in the 1960s, people quickly grasped the concepts of these new-fangled oscillators, filters and contour thingies, the second generation of players shied away from the concepts of FM, to the extent that most FM synths were used for little more than their presets and the professionally programmed sounds that you could buy for them. Even today, if you look closely at Thor’s refills, you’ll find very few patches based upon its FM Pair Oscillator. This is a great shame, because FM is a very elegant system capable of remarkable feats of sound generation. So, this time, I’m going to introduce you to the principles of FM, and show you how to create what may well be your first FM sound.
In this tutorial, I’m going to show you how you can imitate analogue filter resonance using Phase Modulation synthesis, and offer two examples – a bass patch and a lead synth sound – that illustrate how you can use this.
Here’s a patch that I call “Grod’s Reso-Bass”:
I’m sure that you’ll recognise this type of sound, which was inspired by some old – but wonderful – analogue bass pedals that I used in the 1970s. Given that this sample was generated by Thor, it isn’t analogue of course, but it’s a great ‘virtual analogue’ sound, isn’t it? Don’t you just love that deep, resonant filter sweep? Except… this isn’t a virtual analogue patch, and that isn’t a filter sweep. Four modules generated this, and not one of them is a filter. The patch comprises just two oscillators and two envelope generators, and it’s another example of the brilliant Phase Modulation system developed by Casio in the 1980s, which has been almost universally (and unfairly) derided ever since.
Phase Modulation is a brilliant method of synthesis championed by Casio in the 1980s. It enables a digital (or hybrid analogue/digital) synth to generate an enormous diversity of sounds – ranging from traditional analogue to FM in character – using a minuscule amount of wave memory and, by modern standards, minimal processing power. This made it possible for the company to develop a family of polysynths that were cheaper than almost anything that had come before, but were more flexible than pure analogue synths costing many times more. For people who thought of the CZ series as the “poor man’s DX7″ and didn’t rate them very highly, they proved to be surprisingly successful. For people who understood them fully and knew how good they could sound, they proved to be surprisingly unsuccessful. But what, exactly, was Phase Modulation? To answer this, we need to delve briefly into the realms of geometry. (I could explain it with pure maths, but you’ll prefer the geometry, believe me.)