## Tone generation and Subtractive Synthesis 101

Last post we cover the ADSR envelope here. I know this concept is a little difficult to get your head around but stick with it. The pay off is completely worth it.

What you’ll need for today:

1 ) A Synth plug-in. Today I’ll be using TAL Elek7ro – Mainly because it’s free, non DAW specific and you can download it here.

2) Spectrum analyzer: If you don’t have one, grab this.

So what is Synthesis?

Fundamentally all sound sources can be broken down into a mathematical relationship of tones. How these tone can be created, expressed and interact is some seriously high level math. As in…a basic saw wave looks like this…

Input: Peak amplitude (A), Frequency (f)
Output: Amplitude value (y)

y = A - (A / pi * phase)

phase = phase + ((2 * pi * f) / samplerate)if phase > (2 * pi) then
phase = phase - (2 * pi)

Looking that over, I smell fear in some of you right now but don’t stress there is no math involved today.

What you need to know?

All sounds have two main components, they are:

Fundamental – This is the lowest pitch of the sound and forms the start point from which the partials emerge. The main function of the fundamental is to provide the pitch information. C C# etc.

Partials/Harmonics/Overtones – different form of sonic information. All sounds will  have combination of these and this combination is what provides the instrument’s characteristic information or timbre. It’s this part that lets you tell a shaker from a bell even if the pitch (fundamental) is identical.

So?

This knowledge is amazing useful if you’re interested in re-creating or creating new sounds and textures. Understanding the function of the fundamentals/harmonics and the way they interact should give you a head start in implementing desired timbrel quality into your own sounds.

So many different types of Synthesis, I don’t really understand the difference?

The basic idea of all synthesis is pretty much the same, the route they use to get is a little different and as such they all have there own unique qualities that are useful in different circumstances.

Follow these links for a deeper overview about the various different types of synthesis: subtractive synthesis, additive synthesis, wavetable synthesis, frequency modulation synthesis, phase distortion synthesis, physical modeling synthesis and sample-based synthesis )

But today, we are going to look at subtractive. It’s the simplest to grasp in terms of design, common in all styles of music and is a great way to understand the fundamentals that we are going to build on later with other types of synthesis.

What is Subtractive?

In a Nutshell: You build a complex tone using simple wave shapes, then by using a combination of filters and manipulation of the ADSR curve you reduce or “subtract” it into it’s final sound.

Let’s look at the various basic wave forms and build on from there.

Basic Wave Forms:

Sine – Pure fundamental, no additional harmonic information.

Pulse wave- is rectangle in shape and depending on the pulse width (normally labeled PW) can contain a range of both even and odd harmonics. Setting the pulse width somewhere in the 50% region will turn it into into a square wave. Some synthesizers will have a Square setting, some will have a Pulse and a Pulse width.

Saw – Contain both even and odd number harmonic information.

Triangle – Contains mainly odd harmonic information, similar to the pulse wave except due to it mathematics equation it uses the high harmonic content will roll off alot faster.

Noise- Just that random harmonics. Useful but not exactly musical.

Even and odd order harmonics is a whole other topic that I’ll cover at a later date. But a sound with more even harmonics is warm and musical. More odd order harmonics is harsh and biting.

Getting our hands dirty:

What we’re going to do today is create our own tone and using your DAW we’ll mimic what is happening inside the synth. This is a great way to visually process each step and slows the whole process down.

Okay, so open up your DAW and place the TAL then a spectrum analyzer on the channel strip. It should look like this.

Something like this… Make sure turn down your OSC 3 which defaults on.

Create C3 midi note and hit play.

In this section. Click Sine. Now look the analyzer. See how you got one pure tone or your fundamental.

Push the Sine. Use the Semi tone knob to ensure the pitch match the note being played

Yeah, Pure tone

Well… not quite

Now you’ll notice here that there is additional overtones occur. Not a pure sine wave but close.

Click the triangle and look at the way the upper harmonic content filters off rather than on the pulse or saw.

Below the fundamental you’ll see what is refer to as a sub-harmonic.

Click through the other basic waves. Take note of the way the sound changes with each wave.

Making Our Own:

Now let create our own custom harmonically rich sound. Drop the Tal Bitcrusher or any sort of distortion (harmonic generating) plug in on it. Play around with parameters and keep your eyes on the spectrum analyzer. Watch the way the additional harmonics shape and change the wave form.

Find a cool tone and then render the sample as a 1 bar audio loop.

We have now just created a tone ready to be shaped.

Tune in next post as we going to continue on and use both filtering and the ADSR envelope to shape the sound further.

Awesome.

Braydon