SFX Machine Pro, winner of an EM 2007 Editors' Choice Award, takes a novel and somewhat quirky approach to effects design. One of the best ways to learn how to use it is to analyze and modify its factory presets.
I like to insert SFX Machine Pro as a prefader send effect, and then feed it an audio track holding a variety of short loops (drums, bass, keyboard, guitar, voice, and so on) and a virtual instrument with a simple sound (such as a sine wave). That gives me a broad range of material for auditioning changes, and I can use the track and return faders for before-and-after comparisons.
Soul of the Machine
FIG. 1: In the glitchless pitch-shifter, the top and bottom rows of modules render the same time-stretching process with a 180?degree phase shift.
SFX Machine uses eight identical signal-processing modules, each with a source, a single DSP process, two postprocess modulation routings, and an output. The source can be incoming audio or an internal generator, and you can mix in other modules' outputs. You can map all seven front-panel sliders to multiple module parameters, and you can apply MIDI remote control and host automation to them.
Load the Pitch ±100 Cents preset from the Pitch Shift bank; the sliders are assigned to pitch-shift, LFO rate, delay time, and output volume. Audition the effect while moving the sliders; the first three sliders affect pitch, and the output level pulsates. Next click on the Preset Editor button to expose the module layout (see Fig. 1).
All eight modules are in use, but the top and bottom rows are almost identical: the differences lie in the modulation destinations and oscillator phase settings. Notice that toggling module 7 out of the circuit increases the amount of pulsating. With module 7 on, the top and bottom rows crossfade, which is the purpose of the different phase settings. Leave module 7 off and concentrate on the top row.
What's Going On
When unraveling a preset, I start at the output — module 3, in this case. Module 3 appears to do nothing; it has no source, process, or modulator. That's a baffling but common SFX Machine trick. Module 3 actually gets input from module 2's top modulator, which is set to Mix with destination 3 — meaning that it provides module 3's input. Module 3's amplitude is modulated by module 4 acting as a sine-wave LFO. Because amplitude modulation always applies at a module's input, you need to use module 3 to adjust module 2's output. Modules 4 and 8 are identical but 180 degrees out of phase, and that's how the crossfading is done. Here's why.
You pitch-shift by modulating module 2's delay time with the sawtooth LFO in module 1. The negative LFO frequency produces a ramp-down sawtooth causing the delay time to decrease. That results in linear time compression until the sawtooth resets, causing a glitch. Module 5's sawtooth is 180 degrees out of phase with module 1's, and the crossfading provides the deglitching. To calculate the pitch-shift ratio, multiply the settings of the first three sliders, divide by -50,000, and add 1 (see Web Clip 1 for details).
You can now make a variety of modifications. I like to assign the bottom-row ModAmp, Delay Time, and LFO Frequency numericals to their own sliders. That way you can crossfade between different pitches. If you use different LFO frequencies, the crossfade will also move in and out of phase.
You can add a process to modules 3 and 7. Resonant filters with cutoff modulated by the sine waves from modules 4 and 8 add an interesting auto-wah component. You might also change the waveforms of the module 1 and 5 oscillators, though that moves away from the pitch-shifting paradigm.
Use automation and real-time MIDI control of the sliders to add motion. And don't limit yourself to monophonic source material; pads and exotic ambiences make great sources. Percussion works well with long delays and slow, offset LFO speeds (see Web Clip 2).
Len Sasso gives special thanks to SFX Machine creator Earl Vickers for patiently explaining many SFX Machine intricacies.