PolyBrute FM: How DIGITAL can analog oscillators sound?
Whether it's oscillator crossmod, filter FM, wavefolding using the metallizer, audio rate LFOs, or audio rate looping envelopes, the PolyBrute offers more than a few ways to get those glassy, metallic FM tones using analog oscillators. Being an analog synth with exponential FM, it is a glitchier, more organic form of FM, yet you can still achieve some surprisingly clean results (and sometimes the glitches are the whole point!). Here are 5 patches that explore the possibilities.
These and other PolyBrute Explorations patches available here:
https://lwsteely.wixsite.com/modeswit...
If a carrier operator is just a shapeable oscillator + an amp envelope + some kind of keytracking, we have five things on the PB that can act as carriers: VCO1, VCO2, the Noise osc, the Steiner filter (self-resonating), and the Ladder filter (self-resonating). The LFOs and looping envelopes can also generate sound at audio rates, but you have less control over level and keytracking, so these are pseudo-carriers.
If a modulator is just some kind of timbral waveshaper + an envelope, then possible modulators are VCO2 (when used with the FM modes), VCO1 metallizer, Steiner Brute factor, Ladder distortion, Noise color, and VCO waveshape controls, controlled by either the VCF or Mod Envelopes.
00:00 Operratic
An example of a four-operator sound. Carriers = VCO1, Steiner filter (self-resonating). Modulators = VCO2, Mod Env+Metalizer. This patch uses Filter FM on the self-resonating Steiner filter to create its bell-like, glitchy, slightly inharmonic tones. This is blended with Vco1 modulated by Vco2. The Mod Env creates a bright attack using the Metallizer to give the impression of an additional modulator.
3:42 FM Vibes
A vibraphone-type sound that uses Ring Mod to create a tremolo effect. Velocity controls the brightness and envelope timings.
4:07 Tiney Dancer
A classic DX7 e-piano sound, this patch gets its glassy sound from the metallizer rather than FM.
4:57 Crude 0perator
Depending on the how it's played, it can either sound like a broken DX7 or a gamelan. Osc2's sub operates on Osc1 at a ratio of 2:1, and on the Steiner (self-resonating) at 1:1. Envelopes are highly velocity sensitive, using the Amt+Times Natural envelope setting for more realistic mallet strikes.
5:44 Ratioed
The keytracking on Vco2 is zeroed out in the matrix to create a fixed-frequency oscillator, which operates on Vco1. As you play different notes on Vco1, the fixed frequency creates different FM ratios on each note, creating a kaleidoscope of metallic, inharmonic timbres that works well with the arpeggiator in random mode.
Some general tips for FM on the PB:
Let the synth warm up and run a calibration to get the oscillators as stable as possible.
For the most predictable and harmonic results, use triangle waves for both the carrier and modulator, and set FM 2-1 to around 50%. Above 50% it starts to go out of tune, a byproduct of exponential FM.
Better yet, use the sine sub on Osc2 to modulate the Steiner in self-resonance mode to get true sine-on-sine FM. Turn keytracking to 100% and tune the Steiner carefully (PB Connect gives more precision) to make it behave like an oscillator.
In operator-based FM, each modulator has its own envelope. This can be simulated by using an envelope to modulate FM 2-1 or Vco2-Vcf1.
Add velocity to all envelopes using the Amt+Times Natural setting for realistic mallet strikes.
Mod Env to Metallizer can be used almost like an extra operator, to create short bright attacks.
At audio rates, the Lfos can be used as fixed-frequency mod sources (I've tried keytracking the Lfo rates, but it doesn't work very well).
FM sound design is very additive. Think about decomposing the sound you want into transient, attack, and body, each with its own timbre and envelope. Oscillator Sink's OpSix videos are amazing sources of inspiration.
Small tuning ratios (1:1, 2:1) give metallic timbres, higher ratios give glassy timbres. Slight detuning of the carrier and modulator creates bell-like inharmonics.
You can create a 'Coarse Ratio' control to help dial in FM 2-1 timbres. Set Vco1 Tune Mod to Octaves/Fifth, setting Vco2 Tune Modulation to 'Follows Vco1', and then making Mod Env modulate Vco2's pitch (try +36st to start). With the Mod Env ADR set to zero, the sustain slider now acts somewhat like a coarse ratio control for the modulator.
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