Cursus Iteritas Percido#

Wavetable oscillator with envelope and One Knob to Rule Them All

Overview#

Cursus Iteritas Percido is the second module in the Percido line of powerful synth voices. Similar to its predecessor, the Loquelic Iteritas Percido, CIP takes the sounds of the original Cursus Iteritas and adds the musical envelope from LIP with attenuverter-controlled routing to each knob. With the addition of the performance-oriented Master Blaster and CV outputs, CIP is a powerhouse of incredibly versatile synthesis.

• Type: Synth voice
• Size: 24HP Eurorack
• Depth: 1 inch
• Power: 2x8 Eurorack
• +12 V: 105 mA (60 mA if using 5 V supply)
• -12 V: 60 mA
• +5 V: 75 mA (optional)

Etymology#

Cursus-- from latin Cursus 'series'

Iteritas -- from Latin itero 'repeat' with suffix -tas 'state of being'. "Repetitiousness"

Percido -- from Latin 'Danger'

"Dangerous Repetitiousness Series"

Input & output voltages#

All CV inputs respond to 0 V to 5 V, except pitch, which responds to 0V to 8V. The Env and MB Out are 0 V to 5 V. Sync responds to a rising edge around 2 V, and Trig responds to a rising edge around 3 V.

Power#

To power your Noise Engineering module, turn off your case. Plug one end of your ribbon cable into your power board so that the red stripe on the ribbon cable is aligned to the side that says -12 V and each pin on the power header is plugged into the connector on the ribbon. Make sure no pins are overhanging the connector! If they are, unplug it and realign.

Line up the red stripe on the ribbon cable so that it matches the white stripe and/or -12 V indication on the board and plug in the connector.

Screw your module into your case before powering on the module. You risk bumping the module's PCB against something metallic and damaging it if it's not properly secured when powered on.

You should be good to go if you followed these instructions. Now go make some noise!

A final note. Some modules have other headers -- they may have a different number of pins or may say "not power". In general, unless a manual tells you otherwise, do not connect those to power.

Interface#

Pitch

Sets the pitch. Turn to adjust fine tuning, press and turn to adjust coarse tuning. Encoder sums with the pitch CV input.

Mode

Sets the behavior of the envelope.

• In Trigger mode, CIP expects a trigger input to start the envelope. CIP triggers on the rising edge and expects a voltage of about 3 V.
• 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 CIP.
• Free-running mode is the original Cursus Iteritas. The oscillator will continue to run. A trigger in will still reset the envelope on the trigger rising edge, but will not affect the volume.

Algo

Selects which orthogonal function set is used to produce the wavetable.

• Daubechies – uses wavelets
• Fourier – uses sine waves
• Walsh - uses the Walsh Transforms

Hit

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

Time

Controls the length of the envelope.

AT/DC

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.

Shape

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

Center

Selects the center harmonic used to build the wavetable

Width

Controls how many different harmonics are used to create the wavetable

Balance

Allows selection of harmonics included in the output.

Edge

Controls the oversampling filter of the wavetable. As this is turned to the right, it will add musical overtones.

Fold

Wavefolder. Awesome.

MASTER BLASTER

One knob to rule them all.

Master Blaster is a performance-oriented master attenuverter for all envelope sends. At center, all sends are off. Fully clockwise, all envelopes send the full amount set by their respective knobs. Fully counterclockwise, all envelopes send the inverted full amount set by their respective knobs.

MB Out

0 V to 5 V output based on the position of the MASTER BLASTER knob to send to other modules.

Sync

Triggers edge-based oscillator reset.

Trig

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

Env Out

Output to send envelope to other modules.

Audio Out

AC-coupled audio output.

Patch tutorial#

Big Kick

No description necessary. Mult a trigger to Sync and Trig inputs. Patch Audio Out to your mixer. Tune CIP down low; you can’t go too low with a kick! Play with Master Blaster and the envelope Time to change your kick on the fly. For some added crunch, turn up the Fold knob!

Synth Bass

Technically, it's an electric bass, right? Patch a pitch sequencer to Pitch. Patch a trigger to Trig and Audio Out to your mixer. Instant bass! For some variation, patch a CV sequence to Time to add some movement to your bassline.

Organ

Smooth! Patch your pitch sequencer to Pitch (green). Patch a trigger to Trig (red)and Audio Out to your mixer (blue). Beautiful! Who says Beethoven wouldn’t have played modular synths? Bonus points if you program your pitch sequencer to make CIP perform Bach’s Toccata and Fugue in D minor.

Tone generation#

Cursus Iteritas Percido generates a spectral description based on knob positions. Center, Width, Balance, and Edge determine amplitudes for each harmonic. This description is fed into the inverse transform for the current function set to produce the time-domain wavetable. The wavetable is normalized to reduce amplitude variations across spectral changes. Oversampling of the wavetable depends on pitch: lower octaves have higher oversampling since the sample rate only varies by a factor of two. The Edge control interpolates the oversampling from point sampling to a cubic-spline interpolation (NURBS). As the period of the full length of the wavetable always evenly divides the sample rate, the additional aliasing is largely harmonic in nature. Fold controls the signal wavefolding. In many places in the signal path, there are soft clipping stages to mimic analog-style clipping to give more warmth and complexity to the sounds generated.

Variable sample rate#

Cursus Iteritas Percido uses a sample rate that is a multiple of the fundamental (lowest) oscillator frequency. This moves alias power that is a multiple of the fundamental to be mapped to a multiple of this tone, therefore making the aliasing align with the harmonics of the tone. This works well for settings with a strong harmonic structure (spread fully clockwise or fully counterclockwise) and adds unique aliasing character for other tones.

Tuning calibration#

CIP comes pre-calibrated, and should not need adjustment. On the off chance the trimpot gets bumped and needs a tuneup, follow this procedure to recalibrate your module.

Pitch calibration is controlled by a linear resistor-divider network. To calibrate the tuning, attach a voltmeter (preferably 4+ digit) to the test points CAL and GND on the rear panel and adjust the trim pot.

The voltage measured should be 5/16 (.3125) times the input voltage applied to the CV input. A reasonable way to tune the scale is to use an adjustable voltage source to generate 4 V then adjust the tuning trim until the test points read 1.2500 V.

CIP can also be tuned using a reference supply capable of generating a 1 V difference and using a stroboscope such as the Peterson 490 to tune an octave interval. This method is preferred to the meter-only method.

Voltage supply#

Cursus 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.

Design notes#

A while back, our friend Derrick (aka Baseck) called us up and said, "Come over, you have to see this!" We've known Derrick a while. If you're into Eurorack, you've surely seen some of his completely insane demos. We learned a long time ago that when he says he has something that is worth a look, it IS.

Derrick had put together a patch with the Cursus Iteritas and a load of pitch envelopes routed in. We walked away from this afternoon with a blog post and ideas for a few modules. The first was the Roti Pola, a CV mixer that we were inspired to make entirely because of Derrick's workflow, but the second was the Cursus Iteritas Percido. When we started designing it, Markus, the new addition to the NE team, suggested the inclusion of the Master Blaster knob to make live performance with the CIP even more badass. We mocked it up in software and knew it was a winner. Pretty quickly Markus suggested a Master Blaster output so a MB-controlled CV could be sent to other modules as well -- control multiple modules with a single knob! Simplicity.

Warranty#

We will repair or replace (at our discretion) any product that we manufactured as long as we are in business and are able to get the parts to do so. We aim to support modules that have been discontinued for as long as possible. This warranty does not apply to normal wear and tear, including art/panel wear, or any products that have been modified, abused, or misused. Our warranty is limited to manufacturing defects.

Warranty repairs/replacements are free. Repairs due to user modification or other damage are charged at an affordable rate. Customers are responsible for the cost of shipping to Noise Engineering for repair.

All returns must be coordinated through Noise Engineering; returns without a Return Authorization will be refused and returned to sender.

Please contact us if you think one of your modules needs a repair.

Special thanks#

• Derrick "Baseck"
• A conversation with Scott Jaeger (The Harvestman) and Yasi Perera led to the development of the original Cursus Iteritas