Part One: Basic Knowledge – Oscillators and Filters
In this article series we are going to have a look at synthesizers! We will start with the very basic knowledge and use it then to understand complex sound design, unique workflows and different types of synthesis.
Generally speaking, Oscillators are responsible for generating the sound of a synthesizer! Often referred to as VCO’s (Voltage Controlled Oscillator), they can be different types of waveforms like Sine, Triangle, Sawtooth, Square or several others.
While the waveforms pitch is usually set by the MIDI Notes the synthesizer is receiving from MIDI Keyboards, Sequencers or MIDI Clips, the tonal color of the sound depends on the type of waveform. We are talking about fundamentals and overtones on the frequency spectrum here. Take a look at those two:
The left waveform is a saw wave and is defined by its rich overtone structure. The right one is a sine wave and consists of the fundamental frequency only. Fundamental frequency means the general pitch of the note played. Waveforms like Saw or Square have so called overtones. Those are frequencies relative to the fundamental in a musically pleasant way. Try it out for yourself, the difference of the waveforms is an easy to hear thing!
All Oscillators, no matter which Synthesizer you are using, will have most of the parameters in common, such as Octave, Semitones, Fine-Tune/Detune. Those control the pitch of the Oscillator and can change it relative to the received MIDI Signal.
While Octave and Semitone shifts are easy to understand, the pitch amount of Detune/Fine Tune will usually be +-50 cents, which is half a semitone and gets used for sound design a lot! The parameter octave sometimes ranges from 32 to 2, which comes from pipe organs and works the same way as other designs.
Furthermore, oscillators will always have volume control (also called Level) and sometimes shape control which changes the waveform. There’s plenty more parameters, such as Sync or Ring Modulation, that we will talk about later.
Another important part, that almost every Synthesizer will feature, is a filter section. If you are a DJ, you will know what this is about: Filters manipulate the frequency spectrum by taking away either the higher frequencies (Low Pass/High Cut Filter) or lower frequencies (High Pass/Low Cut Filter). But did you know there’s a lot more to know about filters? There are variations such as bandpass, which cuts both the low and high frequencies, or format filters as well as a variety of parameters controlling the sound of the filter.
The most important and most fun to play with parameter is the Cutoff knob, sometimes referred to as Frequency, because it sets the frequency the filter should start to work from. Setting a Low Pass Filter to 500 Hz will cut everything about this frequency. How much the filters cuts is determined by the the Q-Factor, which in many Synthesizers is variable from 6 to 24 db per Octave. Octaves are doubled frequencies, so in our example with the Cutoff set to 500 Hz and a 12db per Octave Filter the Volume will be lowered by 12 db at 1000 Hz.
Another parameter of high usage is the Resonance. If you take a look at the filter curves in the picture above, you can see the little increase in the curve right before it falls. This is the resonance, lifting the frequency the cutoff is set to. The higher you put the resonance, the more this frequency is pushed and eventually results in squeaky sound. This is used for typical Acid sound!
Changing those parameters will effect the sound heavily – Sweeping through the frequencies with a cutoff knob is completely different with a high resonance, than with a low resonance instead.
Filters are fun!
In the next article, Part Two: Basic Knowledge – Envelopes & LFOs, we will talk about basic modulation in synthesizers.
written by Kos:mo for weltsound