Synthesis 101 – Lesson 2 – Oscillators

Synthesis 101 – Lesson 2 – Oscillators

Let’s look at the Oscillators in more detail.  Oscillators in general are very simple.  They constantly oscillate at some frequency set by some knob or slider (potentiometer.)  We noticed that if you directly connect the output of an Oscillator into a mixer, you hear a tone.  That tone is produced based on the waveform that it produces.

Let’s talk about some of those waveforms:

1. Sine
2. Triangle
3. Saw
4. Square/Pulse
5. External Input

Majority of the synths have 2 or more of these waveforms that the oscillator may produce.  Some produce more, but in a nutshell, they produce some waveform of a certain frequency or cycles per second that  produce a tone.

So what is the difference between Analog, Digital or even a soft synth?  If you look at the high level, nothing.

1. Analog synths (VCO) oscillate voltage from some negative value to some positive value or from 0 to some positive value.
2. Digital synths (DCO) oscillate by simulating the process of producing voltage signals using a Digital to Analog converter where the voltage is mathematically interpolated in the digital domain before converting over to Analog.  This may cause artifacts (but can be very difficult to hear the artifact) but it benefits over the analog oscillator by eliminating tuning instability.  Digital synths may also use what is called a single cycle waveform or even multi cycle waveform samples recorded from analog synths to emulate the sound very accurately.
3. Soft synths work the same was as digital synths using either the mathematically interpolated or sampled waveform method to oscillate, however, there are new software (and some hardware) that will emulate analog circuit behavior by modeling the sound based on the electronic circuitry emulation of the original synths (which will create the same artifacts of the original synths, good or bad.)

So does it really matter if it is a VCO, DCO or looped waveform playback?  Not really.  The purists may say it does, but it really doesn’t.  The other question I am asked often is if the Oscillator has similar characteristics (waveform, octave, sync, etc.) can I create a similar sound in software or digital synth in comparison to the analog counterpart?  The answer is yes, very close.  The difference in the final sound may be some different components or module of the entire synth signal path.

Let’s talk about some other parameters or buttons/knobs of an oscillator:

1. Frequency – Coarse
2. Frequency – Fine Tune
3. Pulse Width
4. PWM (Pulse Width Modulation)
5. FM (Frequency Modulation)
6. Sync

Frequency Coarse is what you set the frequency at.  Some synths have settings like Octave ranging from (-2, -1, 0, +1, +2), some just have a knob per OSC.  But in a nutshell, you are going to set the frequency for that OSC.  The best way for a variable coarse knob, is to tune it so when you play the scale, it corresponds to the notes on the scale regardless of how high or low the actual pitch is.

Frequency Fine-Tune is to get the tuning perfect (or not, which is also known as Detuning).  I use the Course knob or setting to get close to the tuning I want, and then I use the Fine-Tune knob to get it dialed in perfectly (I use a tuner for this.)

Pulse Width is the width of the pulse in a Pulse waveform (kind of looks like the Square but not really after you adjust the width.)  The fantastic part about Pulse Width is if that is a modulation capable knob or parameter on your synth, you can have a modulating pulse wave that changes shape based on the frequency and range of the modulation source.  We’ll talk more about PWM or Pulse Wave Modulation in another lesson.

Frequency Modulation, or FM, is the ability to take a source and modulate it using a set or variable frequency.  It is another modulating source, but it impacts the waveform of the original oscillator based on the frequency that the FM source is modulating at.

Sync is used to take two oscillators and have one sync to the other.  So if OSC 1 is the source, and you can sync OSC 2 to OSC 1, both OSC 1 and OSC 2 will be in sync.  The cool part with analog hardware is there is still a subtle drift at times, though it is very much closed to locked in.  Detune is what makes that variable very pleasant to our ears for some patches.

More to come so stay tuned.