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2. FM Synthesis with Fathom CM

1 In this tutorial, we’re going to create a chromatic percussion patch of the sort for which FM synthesis is known. Starting with a blank slate, we go to our Audio Components and open the Oscillator category. From there, we go to the Alias Free subcategory, where we’ll find the Basic Waveforms component and drag it into our patch window.

4 We now have a new window devoted to modulation. Activate this modulation by moving the Synthesis slider to the right-most position for FM synthesis (the left-most position activates AM, or amplitude modulation). This has an immediate effect on the timbre, producing a reedier tone. The display above reveals a more harmonically complex sound.

7 That sounds pretty neat, but it’s more like a calliope than a percussive tone – that’s because our amplitude envelope isn’t very percussive. Let’s click back over to our Signal Flow, and select the Basic Waveforms oscillator for editing. We click the Oscillator button in the lower left, then turn the Volume knob fully down.

2 Classic FM synthesis uses only sine waves as its raw material, so go to the Oscillator editor window down below and find the Waveform knob. Turn this fully clockwise, so that it reads Sin. The display indicates that we’re now generating a sine wave. It’s about as exciting as you’d expect – ie, not at all…

5 That’s still not terribly interesting. However, if you play and hold a note while spinning through the Amount knob, you’ll hear some of the potential on offer. Let’s click the centre of the Amount knob to select it as a modulation target, and then click Add Mod, after which we’ll assign an ADSR envelope as its modulation source.

8 Next, we’ll click the centre of the Volume knob to select it as a modulation target, and assign another ADSR to control its level. We crank the amount of modulation to max, reduce the Attack and Sustain to 0, and set the decay so that it rings out a little longer than that of our first ADSR.

3 We can, however, turn this basic waveform into something far more interesting by modulating its frequency with another sine wave. Doing so will create interesting harmonics not present in either of the original waves. One way to do this in Fathom CM is simply to click the AM FM button at the lower left.

6 Now that we’ve assigned our ADSR to FM Amount, we use the tiny knob on the right edge for the ADSR component to increase the amount of modulation in play to around 0.64 or so. Since we’re making a percussive sound, we’ll reduce the Attack and Sustain time to 0, and dramatically decrease the Decay time.

9 Let’s click the centre of the first ADSR’s amount knob and assign a Key Velocity modulator to it. We can now finetune both the original amount and that of our Velocity modulator until we have a dynamic, woody tone. Back in our Oscillator, we reduce the Pitch Octave to -1.000 for a lower pitch.