The first module in our synthesizer is our oscillator, and this is the sound
creator. It generates sound based on a geometric
wave form. And we have wave forms like sawtooth,
square wave, triangle wave, sine, and noise.
And most of them get their name just by their shape.
If you look at a square wave it is very squarish.
If you look at a sawtooth wave form it does look kind of like a saw blade.
The oscillator is always just putting out sound.
Later in the signal flow, that sound will be turned on and off, and we tend to use
very, very bright sounds in the very beginning.
The sawtooth and square waveforms are really brilliant, harsh, kind of
obnoxious, truthfully; which is why we use the filter after the fact.
But another name for this oscillator is a VCO, a voltage control oscillator, and
that's the important thing about synthesis.
because we do have just general oscillators, like built into mixing
boards, for test tones. But they don't change over time and
that's the key to the synthesizer oscillator is that it can be modulated.
It can change over time, and all these modules have one specific thing that
changes over time. And in the oscillator, it's the pitch or
frequency, which makes sense, because if you think about a synthesizer, one of the
most important things is that you play up and down the keyboard.
And it changes to be the correct note. Well that instance, that idea, the
playing of it on the keyboard is changing the note.
That's an example of modulation. That's key position modulating the pitch
of the oscillator. So we can see that this, this idea of
modulation is that time dimension. How is the oscillator going to change
over time, and there are many things that can modulate the oscillator.
I modulate the pitch of the oscillator and the key position is one of the most
important ones. Now I think it's important that when you
start getting into synthesis, to appreciate the sound of the different
wave forms, and we tend to associate the square wave with kind of a hollow sound,
and the sawtooth waveform with kind of a bright brilliant sound, and there's a
good reason for that. If we look at the harmonic structure of a
square wave, it's missing the even partials.
Kind of jump we have, one, three and five.
But if we look at a sawtooth waveform, it has them all, and it starts to sound more
full. Now this is interesting because when you
start listening to real instruments, you can start to picture, is that more saw
wavish or square wavish. And actually the shape of the wave form
is related to how the sound is actually initially created.
So, if we think of a clarinet, we usually associate a clarinet sound with more of a
square wave shape. And a clarinet does have like a hollow
kind of sound to it. And if you think of how a clarinet makes
its sound, it kind of makes sense that it would be square waveish.
You'll over reed right, the players mouth, and that reed goes up, let's the
air through, closes down, opens up, closes down, opens up, closes down, very
fast right vibrating on and off. But it's like a switch, turning on,
turning off, turning on, turning off, and that creates a square wave-ish shape, and
if we're trying to emulate a clarinet we actually start with a square-wave
waveform. If we're trying to emulate say, a string
sound, like a violin, a bow on a violin, we have a horsehair bow with sticky rosin
on the bow, and it's pulling against that string.
And as it does so, that string goes to the right, right?
It pulls away from it, and then eventually the tension on the string is
so strong it snaps back. We call this motion a slip and stick kind
of motion. And it's related to the wave shape, cause
you can see as it pulls along that string, the string moves up in one
direction, eventually just snaps back to zero and starts over again.
So we get this saw wave-ish kind of shape.
So for emulating a string instrument, we usually start with a saw wave type shape.
So you see, we start getting a language and a way to think about these timbres
and these sounds in a really nice way. So let's look at the oscillator section
of my simple synthesizer, and then we'll move onto the filter next.