Polygon (Polyphonic Synth)

A collection of polyphonic synthesizer units for the ER-301, built and tested on firmware v0.4.27.

These units are built utilizing the ER-301 Middle Layer SDK. Although they would be easy enough to patch manually through the UI, the SDK gives us an incredible efficiency boost. The three voice unit uses about 18-20% CPU, which is a significant reduction from what a comparable UI patch would necessitate.

As a result, we can use Polygon as macro units during patch creation, extending the already massive utility of the ER-301.

Installation

To install, simply download this repo and copy the Polygon directory to your SD card under ER-301/libs.

The new units will be available on the insert screen.

The following units are available:

1. Polyphonic Saw
2. Polyphonic Triangle
3. Polyphonic Single Cycle

Each with 1, 3, 4, and 6 voice variations.

Patching Ideas

1. Use an external midi-to-cv module to send multiple gates and pitches to the ER-301 to use it as a true polyphonic synthesizer.

2. Set the gate mode for each voice to "toggle" (simply hold the M button to quickly edit a control) and use the unit as an oscillator+filter bank.

3. Patch a single gate CV to all the voice gates and manually set the V/Oct tuning to trigger chords.

4. Use the fantastic ER-301 hold mode to set different chord values in the unit and manually interpolate between them ala the THX sound (with much fewer voices of course :P).

5. Create a cheap (as in CPU) bass synth by loading the 1 voice unit and patching your gate input to the sync control. Detune the several secondary oscillators to create interesting new waveforms.

6. Patch an arpeggiator into the round robin inputs for hours of fun!

A Note on Tuning

I created these units using the Squarp Hermod to send polyphonic cv out to the ER-301. I noticed that the pitch tracking on my connection doesn't always work perfectly, especially when spanning several octaves.

Luckily there is an easy fix for situations like this. Simply add the built-in unit Scale Quantizer to your V/octR input to keep everything in tune.

Controls

The polyphonic controls are organized to put the most common controls in the main view and all extended controls inside of sub-views. For example, to see the individual voice gates, simply move your cursor over the gateR control and press enter. This will take you to the dedicated gates view where you can assign individual inputs.

In general, pressing enter on a control should take you to whatever related controls are available or send you back to the main view.

Parameter	Desciption
gateR	A gate for each voice by round robin. When this gate drops the round robin advances to the next voice. As a result, playing legato through the round robin inputs will only use a single voice.
>>>	gateN : the dedicated gate input for the Nth voice.
V/octR	A V/oct for each voice by round robin.
>>>	V/octN : the dedicated V/oct input for the Nth voice. The V/oct input for a voice is tracked as long as its gate or the round robin gate is open on it. If both are active, the V/oct inputs are summed.
syncR	A sync for each voice by round robin. When triggered, this control syncs the oscillators in the currently active voice (it does not advance the round robin). In practice, one would patch the same gate input to both gateR and syncR to both emphasize the attack on each note or produce a consistent timbre.
>>>	syncN : the dedicated sync input for the Nth voice.
>>>	hSync : toggles hard sync for all voices. When active, the secondary oscillators in each voice are hard syncd to their primary oscillators. This allows us to use the secondary oscillators to tune specific harmonics instead of using them as wholly separate notes.
f0	The fundamental frequency for the oscillators in all voices.
>>>	detuneN : the V/oct offset of the Nth secondary oscillator in all voices.
>>>	phaseN (single cycle only) : the phase offset of the Nth secondary oscillator in all voices.
>>>	sLvlN : the level of the Nth secondary oscillator in all voices.
scan	(single cycle only) Selects the sample to use when multiple samples are loaded.
>>>	scanN : the scan offset for the Nth voice.
cutoff	The base filter cutoff for all voices. Each voice has it's own low-pass ladder filter.
Q	The filter resonance for all voices. Starts to self resonate around 0.6.
fenv	The filter envelope amount for all voices. Determines how much the ADSR for each voice affects the filter cutoff. Can also be set to negative values to "duck" the filter.
A	The ADSR attack value for all voices.
D	The ADSR decay value for all voices.
S	The ADSR sustain level for all voices. Can also be used as an overall level control in certain situations.
R	The ADSR release level for all voices.

Screenshots