FM Synthesis is typically regarded as black magic by most amateur synthesizer programmers. The Yamaha DX-7, the first popular FM synthesizer, was
reported to have 90% of maintenance returns complete with their presets intact. You have probably browsed through the presets in Sytrus, and wondered,
'how did they do that'?. The next step, then, is usually to search the Internet for FM synthesis tutorials, only to discover that most of them tell you
how to program a Yamaha DX7, or a particular DX7-like FM synthesizer to achieve a handful of particular sounds. But there's no clear idea how those "FM
fundamentals" apply to Sytrus'. This tutorial will help remove some of the mystery from FM synthesis in general, and help you on your way to understanding
what all those mysterious controls and knobs in Sytrus do.
Operators, Modulation Matrix, or Filters.
This tutorial is all about the Sytrus FM synthesizer, and the purpose behind the most important controls on its variety of control panels. This
tutorial will not discuss each knob and slider, and how each individual control affects the output signal. However, after proceeding through this tutorial,
you will understand:
- What an "operator" is.
- How the modulation matrix is configured to route sounds from the oscillators through the modulators, filters, and effects processing to the output.
- How to apply a filter to an operator.
- The single difference between FM and subtractive synthesis
Step 0: Learn about subtractive synthesis basics
It's fairly easy to get a basic grip on FM synthesis. Starting with simple waveforms, filters and envelopes are applied to get different "effects" on the final sound. With most subtractive synthesizers, you can pick a knob at random, tweak it, and likely hear a difference in the sound that comes out as a result. The 3xOSC or TS404 plugins are a good place to start out. Once you're comfortable with terms like, "oscillator", "LFO", "cutoff", and "ADSR", you may proceed.
Step 1: Understand what you're looking at in Sytrus
1.1 Add a Sytrus channel. Click the "plug" in the upper left of the window, and select the "Default" patch. This patch produces a pure sine wave output. Ignore the 9x9 matrix control on the right side of the window for now.
1.2 Click the "MAIN" box in the upper left to see how the synthesizer's overall characteristics are defined. These parameters operate on the signal that comes out of the synth/filter/pan/fx module. You can apply an overall volume and filter envelope, tweak the basic EQ, add a unison effect, and determine which parameters are affected by the x/y modulation controls.
1.3 Click on the "OP 1" box towards the top of the window. This panel defines "Operator #1". An operator is simply a waveform; some audio signal. You can see one cycle of it in the box in the upper left. The sliders and knobs to the right of the waveform display allow you to modify some characteristics of the waveform. The row of buttons, "PAN", "VOL", etc. allow you to modify the characteristics of the waveform. "OP 2" through "OP 6" allow you to define five more waveforms.
1.4 Click on the "FILT 1" box towards the top of the window. This panel defines "Filter #1". The panel and rows of buttons allow you to specify the characteristics of a filter, which can be applied to the output of the operators. "FILT 2" and "FILT 3" allow you to define two more filters.
1.5 Click on the "FX" button towards the top of the window. This panel defines a basic effects chain consisting of panning, chorus, three delay units, and reverb.
Step 2: Sytrus, the Subtractive Synth, part 1 - The Sawtooth Wave
As a first step in learning how to program the Sytrus synthesizer, we will examine its capabilities as a subtractive synthesizer. This will build on our knowledge from Step 0, above, as we start to learn how to find our way around Sytrus without getting too complicated.
2.1 Go back to the "OP 1" panel, and slide the "SH" slider (just to the right of the waveform display). As you slide it up, the waveform will change from a sine wave through triangle, saw, and square patterns, ending up with a square pulse. Set the slider in the middle of its range (50%) to produce a sawtooth wave. Play some notes and listen to the buzzing of all the high frequency components in the sawtooth wave.
2.2 Now we'll take a look at the modulation matrix. In the Default preset, only one knob is activated. On the far right of the OP1 row, the knob in the "OUT" column is turned all the way up, to 100%. This knob indicates that the output from OP1 should go straight to the output at full volume. Each of the top six knobs in the "OUT" column indicate how loud each of the operators should be in the output mix. The bottom three knobs indicate how loud the output from each filter should be in the output mix.
Step 3: Sytrus, the Subtractive Synth, part 2 - a basic filter envelope
3.1 Now, we'll apply the default filter to the saw wave in operator 1. First, Right-click the OP1 output level knob to mute it. Play some notes. Note that there is now no output from Sytrus. At least one of the various output knobs must be turned on to generate any output. So, to activate the output of filter 1, turn the output knob on the F1 row up to 100%. Play some notes. Note that there is still no output from Sytrus. At this point, we're sending 100% of the output from the filter to the output. However, there's no input signal to the filter, so no sound will be generated.
3.2 To send some of the OP1 signal to the first filter, turn on the knob in the first column of the F1 row, and set it to the full on position, 100%. This sends the output of OP1 to the first filter. The output knob in the F1 row sends the output of the first filter to the output module. Play some notes. The default filter, applied to the saw wave produces a cheap synth horn sound.
3.3 Activate the cutoff envelope for the first filter. Click on the "FILT 1" button toward the top of the window. This displays the Filter 1 settings. Click the "CUT" button in the middle row of buttons. This displays the parameters for the filter cutoff envelope. Click the "ENV" button to display the default envelope. Just under the bottom of the graphical envelope display are four knobs to set the Attack, Decay, Sustain, and Release parameters of the envelope. To the left of these four buttons, is a small, hollow radio button. The default setting is "off", indicating no filter cutoff envelope should be applied. Click the radio button to activate the filter cutoff envelope. Play some notes. Note how the cutoff envelope alters the sound of the "horn". Experiment with the ATT, DEC, SUS, and REL knobs to see how they alter the sound of the wave.
Step 4: An Introduction to Modulation
The modulation operation: Basically, two waves combine in a magic way to create a richer spectrum output. It is important to note that OP1 modulating OP2 (OP1*OP2) does not produce the same output as OP2 modulating OP1 (OP2*OP1). Well, it's not that important, but just know that tweaking the OP1/OP2 modulation parameter will result in a different output than tweaking the OP2/OP1 modulation parameter.
Step 5: Sytrus, the FM synth, Simple Modulation
5.1 First, deactivate the filter by Right-clicking on the OP1/F1 knob. Re-activate the OP1 output by Right-clicking on the OUT/OP1 knob. Play some notes. The sound should be that of the original, unfiltered, buzzy, sawtooth wave.
5.2 Now, apply some modulation to the sawtooth wave. First, play some notes to get a feel for the unmodulated sawtooth wave. Now, click the knob in the OP2 column of the OP1 row, and turn it to a setting of 25%. Play some more notes. Hear how the buzzing quality has changed slightly. Turn the modulation knob from 25% to 50% and hear how the quality of the sound has changed again. Try settings of 75% and 100%.
Congratulations! you've now created an FM synth patch.
Step 6: Filtering a modulated signal
6.1 Now, we'll apply the filter we created above to the FM modulated signal. Deactivate the OP1 output by Right-clicking on the OUT/OP1 knob. Make sure the OUT/F1 knob is activated. If not, Right-click it to activate it. Activate the OP2/F1 knob by turning it to 100%. Play some notes. The sound will be that of a pure sine wave. What's going on here?
Well, what we actually did is route OP2 (an unmodulated sine wave) into Filter 1. Operator 2 is still at its default setting of a sine wave, so the output generated is a filtered sine wave, or, in other words, a sine wave. What we wanted to do is send OP1 into Filter 1. (This may be the most confusing feature of the modulation matrix itself.) This is part of what I mean by OP1*OP2 not being the same as OP2*OP1. Since we configured OP2 to modulate OP1, in order to send the modulated OP1 output to a filter module, we must use the OP1 column of the desired filter row to route that signal accordingly.
6.2 To route OP1 into Filter 1, deactivate the OP2/F1 knob by Right-clicking on it, and re-activate the OP1/F1 knob by Right-clicking on it. Now, we are routing the modulated OP1 signal into the filter. Play some notes. Now, the filter we created above is acting on the modulated signal.
Step 7: The single difference between FM and Subtractive synthesis
Subtractive synthesis uses richer waveforms (triangle waves, square waves, etc.) as the base signal before applying filtering, resulting in higher order harmonic content in the synthesized signal. FM synthesis creates richer waveforms via modulation, resulting in "sidebands" of the carrier signal (i.e. the operator being modulated). That's it. Both use filters, envelopes and modulators on the sound. Once you understand what the knobs in the modulation matrix do, you're off and running.
FM Synthesis can seem intimidating because it does not seem as intuitive as basic subtractive synthesis. The 'sidebands' resulting from the modulation operations are not as easily visualized as relatively simple square waves, or triangle waves. Also, FM synthesizers typically have much more complex envelopes and automation capabilities (see the 'Electrocution' preset for a complex automated filter example), adding to their complexity and intimidation factor.
Tutorial credits: Eric Mitchell.