Loquelic Iteritas Percido#

Complex digital voice

Overview#

Loquelic Iteritas Percido is an extension of the original Loquelic Iteritas. Like Loquelic Iteritas, it is a digital VCO with interpretations of three classic synthesis algorithms involving dual pitch control parameterized by four tone controls. LIP adds an envelope that can be shaped and routed to pitches and tone controls, making it into a free-standing voice.

• Type: VCO/Voice
• Size: 20HP Eurorack
• Depth: 1 inch
• Power: 2x8 Eurorack
• +12 V: 150 mA (80 mA if using 5 V supply)
• -12 V: 5 mA
• +5 V: 90 mA (optional)

Interface#

Pitch A/B

The pitch of each oscillator can be controlled by pitch encoders. Tap encoders to alternate between coarse and fine tuning. The 1 V per octave input serves as an offset . The pitch inputs are cross normaled.

Master

controls the sync of the oscillators. When in the middle position both oscillators are free running. When A is selected, oscillator B will sync to oscillator A; when B is selected, A syncs to B.

Mode

Changes the behavior of the envelope:

• Trig: In Trigger mode, LIP expects a trigger input to start the envelope. LIP triggers on the rising edge and expects a voltage of about 3 V.

• Loop: In loop mode, the envelope will continually regenerate. A trigger in will hard reset it on the rising edge; without a trigger in, it will regenerate based on the parameters set on LIP.

• Free: Free-running mode is the original Loquelic Iteritas. Oscillators will continue to run. A trigger in will still reset the envelope on the trigger rising edge, but will not affect the volume.

Shape

Controls the attack and decay of the envelope. All the way counterclockwise, the envelope is all decay; all the way clockwise, attack dominates. Turning the knob transitions between these two extremes gradually.

Curve

Controls the shape of the curve: counterclockwise gives an exponential curve, while clockwise gives a logarithmic curve. In the center, the shape is linear.

Time

Controls the length of the envelope.

Envelope controls

Six attenuverters that route envelope to pitches and parameters. Positioned at 12:00, the envelope is off and does not route to a parameter. Fully counterclockwise results in an inverted envelope send. Fully clockwise yields full positive send.

Trigger

Input to trigger LIP. The envelope also resets (in any mode) when LIP receives a trigger.

Envelope out

Output to send envelope to other modules.

HIT

Momentary button to manually trigger LIP. When depressed, LIP behaves like it received a rising edge on a trigger.

Audio Out

The AC-coupled audio output.

Patch tutorial#

The easiest way to get to know Loquelic Iteritas Percido is to set the mode to Free, connect the output to your mixer, and start twiddling the knobs and listen.

A good next step is to hook any LFO up to any of the four tone control inputs (Morph, Fold, Modulate, and Damp).

Other interesting effects can be created by controlling the pitches independently (by default the 1 V per octave inputs are normaled to each other). For instance, using a Tonnetz Sequent to produce musical intervals produces interesting results.

Switch the mode to Loop and experiment with the envelope controls and sends. LFOs and other CV sources can be hooked up to envelope controls to vary sounds even more.

Algorithm VO#

As in Loquelic Iteritas, the VO algorithm is roughly based off of the VOSIM algorithm discussed in Curtis Roads's epic Microsounds. This algorithm amplitude modulates a carrier by an exponential to create a complex harmonic structure. The simplest carrier is a sinusoid which produces a spectrum with a Gaussian distribution centered on the carrier. More complicated waveforms produce Gaussians around each harmonic, producing spectra similar to comb-filtered noise. Pitch A is the fundamental frequency of the carrier. Pitch B is the retrigger frequency of the exponential decay.

Controls#

MORPH

Changes the waveform of oscillator A

DAMP

Sets the decay constant on oscillator B relative to its period

MOD

Phase modulates oscillator A by oscillator B

FOLD

Sets the wave fold threshold on the final wave folder

Algorithm SS#

Algorithm SS is a highly modified version of summation synthesis originally developed by James Moorer. The premise comes from a simple mathematical equality between an infinite harmonic series and a relatively easy-to-compute expression:

This equation allows a wide variety of musical spectra to be produced by only two parameters. LIP generalizes the sinusoidal terms into multi-waveform oscillators: two of these track the two input pitches while the third tracks the difference of the two pitches and adds a wave folder for more harmonics. In the equation oscillator A is the left sinusoidal term in the numerator. Oscillator B is the sinusoidal term in the denominator. The equation becomes

Controls#

MORPH

Changes the waveform of all oscillators

DAMP

Sets the a parameter in the equality. This controls the generated spectra with higher values producing higher power harmonics.

MOD

Phase modulates oscillator A by oscillator B

FOLD

Sets the wave-fold threshold on the final wave folder

Algorithm PM#

The PM algorithm is a naive time-domain two-oscillator phase-modulation implementation that combines both oscillators with amplitude modulation.

Controls#

MORPH

Changes the waveform of both oscillators

DAMP

Blends between oscillator A and B through their product (amplitude modulation)

MOD

Phase modulates the oscillators by each other

FOLD

Sets the wave-fold threshold on the final wave folder

Patches#

Kick

It’s a kick drum! Patch a trigger to Trigger. Tune oscillator A to the rest of your patch. Add some Morph, Fold, and Mod to get things more ridiculous.

Sounds Subtractive Emulating a saw wave into a LPF. Patch a trigger into Trigger, and a pitch CV sequence into Pitch A’s 1v/8VA jack. Tune oscillator A down low for some bassy fun!

PM pluck Bassy, plucky, fun! Tune oscillator B up one octave from oscillator A. Hint: to hear the pitch of each oscillator, set the Master switch to the oscillator you want to tune. In this case, set Master to A, tune to taste, then switch to B and tune one octave up from A. Patch a trig to Trigger, a pitch CV sequence to oscillator A’s 1v/8VA jack and you’re off!

Roar Whoa! Tune oscillator B up two octaves from oscillator A, using the technique from the previous patch. Set knobs to match the pitcure, then send in a trigger to Trigger! Try it out in SS mode too for some even wilder sounds.

Actual Subtractive Run the Env Out to a filter like Viol Ruina’s frequency CV input and run LIP through the filter to create a compact subtractive voice.

Calibration#

Loquelic Iteritas Percido is best calibrated using a stroboscope and tuning octaves across the pitch range. Each pitch input has as separate calibration. The pitches can be isolated from each other by using the master switch to force the base pitch to be determined by only one input.

Voltage supply#

Loquelic Iteritas Percido can run its processor on the 5 volt eurorack power rail to reduce noise and load on the 12 volt bus. Gently push the switch tab in the direction of the desired rail to use.

Sample rate#

Loquelic Iteritas and Loquelic Iteritas Percido use a unique multisampling technique to make aliasing more musical. By choosing a particular sample rate for a waveform that has a harmonic structure (all overtones are integer multiples of the fundamental) the alias power can be moved into frequencies that are also multiples of the fundamental and therefore more musical.

This gets complicated when synthesizing two oscillators at different pitches but using the same DAC. The compromise that LI/LIP make is to give up the notion of a fixed sample rate and compute a time delay between samples based on both oscillators. For the single oscillator case, this delay is based entirely on pitch. If this delay is computed based on each oscillator's pitch, both sample rates can be interleaved by checking which oscillator's delay will be up first. This oscillator is then updated to its next timestep and an output value is computed based on both oscillator's output state. This makes no guarantees about exactly where the aliasing goes. It is an attempt to make the aliasing related in some way to the fundamental pitch.

Design notes#

The original Loquelic Iteritas was just a simple implementation based on VOSIM but I soon realized I could pack a lot more punch in this form factor and found two additional algorithms. Loquelic Iteritas was designed to be a functional oscillator for sound designers as well as for musicians. I wanted to maximize the possible sound space given the input controls going from simple calm sounds to extreme, even broken, sounds. The priority of tonal variance led to some sacrifices on the musical side such as the total pitch range.

My wife, Kris, however, had other ideas: her first time playing with Loquelic Iteritas, she said, "This should be a drum." Pretty quickly, we realized that the module was hugely versatile, and people used it in many ways, but Kris was far from alone in recognizing the utility of an envelope and a trigger for Loquelic Iteritas. And we got to work.

There have, as always, been multiple revisions from the functional to the mundane (people at Superbooth in 2017 were treated to a version with one LED so bright it hurt to look at until we covered it with Noise Engineering stickers!), but from the start, we were pretty excited about the expansion of Loquelic Iteritas. It's the largest module we've made so far, but we think it packs a hell of a punch. We hope you agree, and we hope you have as much fun playing with this one as we've had making it.

Special thanks#

Shawn Jimmerson Cyrus Makarechian & Black Line William Mathewson Mickey Bakas Tyler Thompson Alex Anderson Derrick Baseck Anthony Baldino

References#

Jolley, Leonard Benjamin William, ed. Summation of series. Courier Corporation, 2012.

Kaegi, Werner, and Stan Tempelaars. "Vosim-a new sound synthesis system." Journal of the Audio Engineering Society 26.6 (1978): 418-425.

Moorer, James A. "The synthesis of complex audio spectra by means of discrete summation formulas." Journal of the Audio Engineering Society 24.9 (1976): 717-727.

Roads, Curtis. Microsound. MIT press, 2004.