03. Oscillators
To create your own sound from scratch, either for musical use or to design sound FX, you will use 3 families of elements:
- A sound source, would it be an audio sample, an instrument or an oscillator with a basic waveform, it gives the base sound you're gonna work with.
- It will then be processed by different effects. It could be filters, distortion or anything else.
- And you have what I call "control modules", such as LFO and envelopes. They don't make sound on their own but they can control parameters of the sound source and the effects to bring movement in the sound.
In this video we'll focus on the sound source component. And because audio samples can be basically anything, we'll focus on the oscillator first to get the core principles down. But a lot of what we do with them can be done with audio samples as well.
VCO / oscillator
VCO stands for voltage controlled oscillator, and it is the heart of any synthetiser.
For example here on serum there are 2 of them, or here in Ableton's operator there are 4.
The sound they provide depends on the shape of their oscillation, their waveform.
We talked about these in my old video about harmonics and overtones. I will link here and in the description for that.
But to sum it up, the most common waveforms are sinewave, triangle, sawtooth or square wave.
They all sound different and learning to recognize them will help you a lot in your sound design.
The sine has a very smooth and soft sound. (It is often this type of wave form that is used as a sub bass to double other synth sounds.) It is made of only one harmonic. Which means that a pure sine wave is made of only one pure frequency.
The square wave have a more hollow sound.
Without any effect it remind the tone of old video games.
It has more harmonics than the sine so it also sound richer.
With the square, you'll often have a parameter called "pulse width". This would make one part of the wave thiner, as the other part gets wider. The more asymmetric the wave, the more metallic and nasal the sound. It also make it sound a bit more like a sawtooth wave.
Nowadays you often have this "pulse width" for other waveforms too. Like in serum here, along with other morphing options. These are a lot to try already.
The triangle wave is halfway between the sine and the square, both in softness and in harmonic content. It's pretty soft.
And the sawtooth sounds more aggressive, it is also richer in harmonics than the others so it sounds fuller. The fact that it sounds fuller makes it a good candidate to work with filters.
So if you want do make a smooth sound like a flute, you'd might want to choose a sine or a triangle wave.
If you want to make a more aggressive sound, that would sound more like a big trombone or an aggressive bass sound, you might want to go for a sawtooth wave.
In the context of a synth, you can obviously control the pitch of the oscillator with the keyboard, each key giving a different note, but in the context of a modular synth, like in VCV rack, an oscillator on its own doesn't have much controls.
If it's not linked to anything it will only output a continuous buzz. Even to control its volume you'd need a separate module called VCA (for voltage controlled amplifier).
Here, in this setup, I have this module (Audio-8) which is simply my audio output so we can actually hear the sound. The sound is provided by the VCO, the oscillator, that goes to a VCA, the amplifier, then straight to the output.
The VCA acts like a volume knob. And on the oscillator, I can change the frequency (Freq knob). The "fine" knob is for the tuning, so it's the frequency as well but with fine tuning, and the three other knob do nothing at the moment.
But even though oscillators are very basic on their own, you can already do several things with them.
You can stack several oscillators with different waveforms to get new tones. So there are a lot of combinations to try. You can try with 2, 3 or more different oscillators, and also try to change the volume of each one as it can also drastically change the tone.
If you use several oscillators with the same waveform, you can separate them by different intervals to make the sound richer. Usually, an oscillator is doubled by an octave or a fifth.
It doesn't seem much like that, but when you play a melody with it, your brain will hear it like one instrument. And that can help the sound cut through a mix if you double it higher and it can have more weight if you double it an octave lower. This is usually done with a sine or triangle waveform.
If you use two oscillators with the same waveforms, you can also detune them slightly.
Usually an oscillator would be detuned down slightly, and the other slightly detuned up, so it creates kind of a phasing effect. It can thicken the sound and also add some motion. Due to the phase of the oscillators going in and out of sync, it creates a waving sound, kind of a beating in the sound. The more you detune the oscillators, the quicker the beating.
This beating appears because of phase cancellation. When two sound waves play together, they'll be added up. So where the two waves have positive values they'll sound louder, and where they have opposite values they'll cancel each other out.
So here, because the 2 oscillators are slightly detuned, they'll go slowly in and out of sync, and that's the beating we hear.
So when you do that with sine waves or triangle waves, the beating will be more drastic, because they're not made of a lot of harmonics.
If you do that with square waves or sawtooth waves, the beating will be more shallow because they have more harmonics, more frequencies to cover up the holes in the sound.
You can also reduce the effect of that beating by panning an oscillator to the left and the other to the right. That's also a good way to make your sound stereo wide, but keep in mind that if the sound is played back on a mono system, the beating will come back
This detune trick is implemented in serum in a handy way. Here you choose how many voices you want, and with this you can set how much you want to detuned them. You can also reduce the volume of the detuned sound to mix it with the original sound.
Now, technically if you want to play several notes at a time to make chords, you'd need one oscillator per voice. So that would be 3 oscillators to play a chord of 3 notes. But software synths and even some hardware synths don't really bother with that, and they directly give you the option to play polyphonic or monophonic.
While polyphonic allows you to play chords, monophonic also have some advantages.
Monophonic can sound cleaner as there won't be any note overlapping when you don't want them to.
But it also allows to use some glide, also called portamento. Basically it will make the pitch glide smoothly from one note to the next. The more portamento you add, the longer the glide time.
That's a very neat feature that can really transform the feel of your sound. It's very cool to makes sequences with some notes that are linked and other that are detached.
It's worth noting that these oscillators are not the only sound sources you can have in a synth.
You can also have white noise, which sounds like static noise. It is a sound where all the frequencies between 20Hz and 20kHz are present.
It doesn't sound that appealing on its own, but it can be very useful in different situations, like to fill the background of a mix for instance.
It is a good basis to make synthetic hats or snares, and as all the frequencies are present it is also a good candidate to work with filters.
You can also have pink noise, which is similar to white noise, except the higher frequencies are a bit quieter, so it sound smoother to the ear.
More recent synths, like serum, also use wave tables, which allows you have several waveforms on one oscillator. They have a parameter to morph the waveform from one shape to another smoothly, that can create some cool sounds that sound almost alive if you automate this morphing parameter.
Some synthetisers like serum even allow you to draw your own shapes, or imports them from an audio file. Which already unlocks a ton of possibilities with the technics mentioned above.
Talking about audio file, your sound source can also be a sampler, which would use an imported sound directly, so you can play notes with it like with an oscillator. So that could be anything: a drum sound, a live instrument like a guitar or a bagpipe, anything you want.
Right off the bat there are a lot of thing you could do only with oscillators and samplers.
But everything I showed you was all by stacking oscillators upon each other. There's a lot more things you can do with 2 oscillators, and that what we'll see in the next episode which will be about all the different types of audio synthesis.
