Adding Frequency Modulation

The FM (frequency modulation) knob is a fast way to modulate or achieve effects with the SubTractor's oscillators.

When both oscillators are enabled, the FM knob causes Osc 2's frequency to modulate Osc 1. This will add harmonics or interference and noise-like effects. Because it's based on frequency, the FM knob behaves differently depending on how the oscillators are tuned to each other, as you'll hear.

To FM-modulate Osc 1 with Osc 2

1.	Make sure the noise generator is turned off, and enable both oscillators.
2.	With your loop playing, rotate the FM knob to the right (Figure 5.21). Figure 5.21. The FM knob modulates Osc 1 with the signal from Osc 2 and/or the noise generator.

FM has more of an effect when the oscillators play different notes. When tuned an octave, a fifth, or a fourth apart (perfect intervals), the FM knob acts very much like an "overdrive" effect, introducing high-frequency harmonic content and fattening the sound.

Knowing semitone-to-interval relationships is important for tuning in Reason. Also, knowing the right terminology for intervals can save you some embarrassment if you're planning on working with vocalists (or being one). Intervals can be perfect, minor, major, diminished, and augmented.

To modulate between perfect intervals

1.	Tune the oscillators an octave apart by setting the Osc 2 Oct value to 12.
2.	Make sure both oscillators' Cent values are at zero, then tune the oscillators apart a fifth by incrementing the Osc 2 Semi value to 7 (Figure 5.22). (The Semi arrow buttons adjust the oscillator sound by halftones.) Figure 5.22. The Semi control raises and lowers pitch in half steps. At 7, the oscillator is raised a fifth.
3.	Tune the oscillators apart a fourth by incrementing the Osc 2 Semi value to 5.

Tip

• The Cent arrow buttons fine-tune by 100ths of a half step. Detuning "shift" effects are possible when oscillators are tuned apart by 10 Cents or so.

Let's return to the subject of intervals. Perfect intervals are said to be "diminished" when lowered a half step, and "augmented" when raised a half step.

All "imperfect" intervals (anything other than fourths, fifths, octaves, and unison) get their names from the major and minor scales, and are either lowered (minor) or major.

When oscillators are tuned apart using imperfect intervals, the FM effect is more like a noise signal, or interference.

To modulate between imperfect intervals

1.	Make sure that both oscillators are active.
2.	Now set the Semi counter to any interval other than 5 or 7 (see the conversion chart).

Table 5.1. Semitone-to-Interval Conversions (All 12 Tones)

NUMBER OF SEMITONES	INTERVAL
0	Unison
1	Minor second
2	Major second
3	Minor third
4	Major third
5	Perfect fourth
6	Diminished fifth (or augmented fourth)
7	Perfect fifth
8	Minor sixth
9	Major sixth
10	Minor seventh
11	Major seventh
12	Octave

FM modulation and the noise generator

As long as the noise generator is on, it affects the Osc 2 signal's modulating of Osc 1. To hear how this affects the FM modulation knob, let's listen to it by itself.

To modulate Osc 1 with the noise generator

1.	Turn off Osc 2.
2.	Turn on the noise generator.
3.	Turn the FM knob to the right (Figure 5.23). Figure 5.23. When modulating with the noise generator, use the FM knob sparingly.
4.	Play your loopand cover your ears!
5.	Try adjusting the Noise Color knob to see how it affects the sound. When the noise color is set hard left, the noise signal is fluctuating slowly and random pulses will be audible. When the color is set high, there is no pulse effectjust a uniform tonal brightness.