i2 – Instrument interface

There may come a time when you want to marry the rest of your rig with your Eurorack system. The Instrument Interface (I²) is designed to take a wide range of signals and transform them into a set of useful Eurorack compatible voltage levels.
The module uses an envelope follower circuit to achieve direct control of the amplitude of any incoming signal, producing a control voltage proportional to its amplitude. This allows a real and direct communication between external sound sources and Eurorack systems.

The Instrument interface module has the following funcitonal blocks:

“PREAMP”
With two audio inputs (6.5mm jack and Mini-jack), amplification of the input signal is controlled by the “GAIN” pot.

The minimum signal required to generate the maximum envelope is 200mV peak and allows up to 5v input.

“BPF”
The signal will then pass thru a band pass filter with cut-off frequency and bandwidth control via “FREQ” and “WIDTH” pots. This will set the frequency range of our control signal.

After this stage the signal can be accessed at synth level via “AUDIO OUT”.

“ENV.FOLLOWER”
After filtering the signal it will feed into the “RESPONSE” stage which determines the envelope follower’s response velocity. It features a “HIGH”, “MEDIUM” and “LOW” selector switch to achieve the optimal envelope for different kind of signals. “FOLLO OUT” will output the extracted envelope and has a level indicator LED. Green: Medium level; Orange: High level; and Red: Max. Level.

“ENV.REGENERATOR”
“REGE OUT” is a regenerated envelope that allows independent control of the rise part of the envelope with the “ATTACK” knob, and the fall part with the “DECAY” knob.

The Envelope Regenerator also features an LED indicator for the regenerated envelope level. Green: Medium level, Orange: High level, Red: Max. Level.

“TRIG.EXTRACTOR”
With the “THRESHOLD” pot we can control the level of a comparator that determines when “GATE OUT” and “TRIGG OUT” outputs will be activated.

“GATE OUT” is active while the envelope is over the threshold we set, while “TRIGG OUT” is activated just when the threshold is passed.

Indicator LEDS show when the outputs are active.