Synthesis 101 – Lesson 1 – The First Sound
I like to read, but I will keep these lessons as short as possible to get to the point of the lesson.
In this lesson, we will first understand a single oscillator synthesis at its most basic form, the OSC, VCO or DCO (or whatever other form of Oscillator), and the VCA, and how we get sound out of there with and without a keyboard.
What you will need for this lesson and lab are:
(1) Oscillator – We will just say VCO
(1) Amplifier – We will just say VCA
A Keyboard (KEY) or other input device that supports CV and Gate
All potentiometers will be either called knobs or sliders.
Let’s get started.
Oscillators in its simplest form oscillates at a frequency of some value continuously. Many synths have controls for oscillators. They include:
- Frequency (or Pitch – they are not synonymous but for simplicity sakes, let’s assume they are the same) is the number of times a given oscillator complete a single cycle in a second. For example, at 440Hz (Hertz), the oscillator goes through 440 cycles per second or 440 Hertz.
- Octave (you’ll see representation such as 1′, 2′, 4′, 8′, 16′, 32′) where the larger the number of feet, the lower the tone.
- Wave (sine, saw, square, pulse, etc.) creates the shape of the sound.
- And there are more… (but we want to keep this lesson simple)
At this point, we know that a VCO is oscillating at all times when powered, and there is some frequency at how it is oscillating. The rate of oscillation can be changed by Frequency and Octave knobs to create a higher or lower tone. The sound is shaped by the wave type. Now, how do I get the sound to play?
In the simplest state, you can do this:
[ VCO out -> connect to mixer, speaker, headphones ]
Hello World! – Your first synth program…
WARNING WHEN TRYING THIS AT HOME (unless you have a cheap mono speaker that can handle the output). Your speakers should be at low volume, and it should be increased otherwise you will have a very loud tone, and depending on your settings, it can blow out speakers, headphones, etc.
NOTE: We built one with a 3.5mm mono cable and it is great for troubleshooting Eurorack. Easy to do in 3 steps:
- Find a mono speaker in a device that is no longer working like a speaker phone or a child’s toy and remove the speaker
- Find a mono 3.5mm cable that you can reuse or find a solderless plug
- Connect the positive connection of the speaker to the Tip and the negative connection to the Ring
OKAY – Digression is over.
So, connecting the output of a VCO creates a steady tone. You can tweak the knob that corresponds to Frequency, Octave, or Wave and get different sounds. However, it would be nice to connect it to something that controls the volume. That is where the VCA helps. Turn the knob of the VCA all the way down to 0 or counterclockwise (in most cases)
[ VCO out -> connect patch cable to -> VCA in ] THEN
[ VCA out -> Mono Speaker ]
Now turn the knob clockwise or increase the Amplifier output. Now you have a Volume knob!
But wouldn’t it be cool if we can use a keyboard to trigger the tone on or off? This is where the GATE out of a Keyboard or a sequencer comes in to play. Let’s look at a simple VCA. There should be a knob, a VCA input and output jacks, and you may see a CV and/or a GATE in. The CV/GATE in here allows for the VCA knob to be controlled. There may even be a CV/GATE knob (which limits some amount of CV/GATE coming in) which we will cover at a later lesson but make sure it is not at 0. Now let’s make sure that the VCA level knob is also set to something higher than 0.
[ VCO out -> patch cable to -> VCA in ] THEN
[ KEY GATE out -> patch cable to -> VCA CV/GATE IN ] THEN
[ VCA out -> Mono Speaker ]
Now play any note on the keyboard. Now the same tone comes out but once the note is released the tone becomes silent.
Last but not least, changing the pitch of the sound with the keyboard. We covered the basic VCO components, except the CV in. On simple VCOs it is simply called CV in. On many, however, it is a plug called 1V/O. This can be a topic in itself, but for simplicity sakes, this input has a range of one octave per 1 volt of current, hence the term 1 volt per octave or 1V/O. The CV out of the keyboard will produce a different voltage out of the CV depending on the note you depress on the keyboard. So we are going to use the CV out of the keyboard to change the frequency of the VCO.
[ KEY CV out -> patch cable to -> VCO 1V/O IN ] THEN
[ VCO out -> patch cable to -> VCA in ] THEN
[ KEY GATE out -> patch cable to -> VCA CV/GATE IN ] THEN
[ VCA out -> Mono Speaker ]
Let’s make sure that the Frequency is set to 0 or center or whatever makes it tone out a standard 440Hz. Fine Tune knob, if it exists, should also be set to 0 or center. Now let’s make sure that the VCA level knob is set to something higher than 0. Play a note, and it should somewhat represent the note coming out of the VCO. Play up and down the scale, and the pitch changes based on the key played. The sound comes out when the key is depressed and it stops when the key is released.
That is the basics of a single oscillator voice. In the next lessons, we will talk more about Oscillators, Filters, Amplifiers, EG or Envelope Generators or ADSR, and LFOs, and how those affects sound.