An Introduction to Self-oscillation and FM Synthesis - Part 1


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This post is part of a series called An Introduction to Self-oscillation and FM Synthesis.
An Introduction to Self-oscillation and FM Synthesis - Part 2

This pair of quick tips will give you an introduction to to often baffling world of self-oscillation and FM synthesis - two processes which are fundamentally linked. I am using Reason 4 for this example, but the principles here will translate to most synths/samplers/DAWs.

In this first installment I will be looking at how rapid triggers and loop points create a self-oscillation effect, which is an excellent starting point to grasp the basics of FM synthesis, not to mention a great technique in its own right. By then end you will have all the skills you need to create an entire track from one basic sample.

Step 1 - Choose a Sample

To get started with this tut we will need to load up an NNXT sampler, initialize the patch and load in a sample. Literally any sample will do, but for this example I'm using a nice heavy snare hit, with plenty of low end as I've always found this to be a winner.

Step 2 - Set the Loop

If you turn the 'play mode' dial below the main window in the NNXTs editor panel you can set the sample to loop when you hold a key down.

By lowering the value of the 'Loop End' dial we can shorten the section of the drum that is looped. As you shorten the loop you will begin to hear the repeated snare hits blur into what sounds like a single tone.

So What's Going On?

To understand what's going on here we need to think about our human hearing capabilities. Roughly speaking we can hear sounds ranging from 30 Hz to 20,000 Hz, though this varies from person to person. Hertz (Hz) measure vibrations per second, so essentially anything below 30 vibrations a second is inaudible to us.

Now, obviously the snare drum is audible to us, and contains many frequencies in the audible spectrum, but the rate at which the sample is triggered is not. When we shorten the loop to the point where the sample is being triggered more than about 30 times every second (30 Hz) the rate at which it is retriggered becomes audible in itself, and we perceive a single tone rather than a repeated sound. This also explains why shorter loops result in a higher note - the 'frequency' of the sample looping is increased.

So How Can We Use This?

Once we have a tone like this we can make use of the other functions of the sampler to manipulate it to achieve literally limitless effects, but for many musical applications we will first need to tune the sample. Play around with the loop points until you find a tone that you like the sound of.

Note: You can also move the 'loop start' point inwards, just make sure to also move the 'start' point inwards by the same amount or you will hear the start of your snare drum at the beginning of every note.

Tuning Your Note

Now we need to manually adjust the 'root' and 'tune' dials so that our note is tuned to the rest of our instruments. Using another instrument play C3, and adjust the samplers controls until when you play C3 on the sampler the 2 notes sound the same. This can be a little tricky if you're not used to tuning other instruments such as guitars - you could use a tuner or tuning plugin (not pitch correction plugin) to help you. Once you're done you can play your sample like any other instrument.

Once you've got this far the possibilities are literally endless - you can use any loop from any sample as a basis and use the sampler functions to sculpt the sound. At this stage you are basically working the loop as an oscillator, and all the common principles of synthesis will apply.

Here Are a Few Suggestions

  • Use filtering to soften your tones and remove unwanted frequencies.
  • Envelopes on filters, amplitude and other controls are a great way to sculpt your sound over time.
  • LFOs can add some great movement to your sounds
  • Use effects to soften or add interest to your sounds.

Here is a basic track I've built up purely using that one snare sample; every sound in the track is made from the sample, using the techniques outlined in this tutorial.

In the next part in this series I will be looking at the basics of FM synthesis, and this will draw on some of the principles covered in this tip.