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Midi-2-cv

Midi 2 CV user manual

The Midi 2 CV is class-compliant but uses an unusual USB setting (1ms poll-rate in low-speed mode) not well supported on Windows.

Optimal latency is obtained with OS X >= 10.6.3 ; iOS ; or Linux >= 2.6.

On other systems, the Midi 2 CV will work but messages will be delayed by up to 8ms. Technical characteristics Range and standards:

CV outputs: 0 to 4V, V/Oct (4 octaves).
Gate outputs: Positive V-trig, ON = 5V ; OFF = 0V.

Performance:

Resolution: < 2mV.
8 points calibration curve for non-linearity compensation.
Temperature dependency: +/- 2 cents within the 10° C to 80° C range.
Output impedance: 220Ω (rule of thumb: 2 cents drop per connection to a CV input).

Power supply:

USB-bus powered, current draw < 20mA. Overview

Sound Study Modular Midi 2 CV is a DIY USB MIDI to CV interface – enabling you to control an analog synthesizer or modular system from a computer or smartphone/tablet equipped with a USB port. The Midi 2 CV is class-compliant and as such, does not require any driver.

It features various conversion/voice allocation modes, covering monophonic, duophonic and drums/triggers applications. Quirks ahoy!

Before moving forward, it is important to state some limitations of the Midi 2 CV – most of them due to its ridiculously simple design:

The Midi 2 CV is a USB device not a USB host! It can be connected to ‘active’ devices such as smartphones, tablets, laptop or desktop computers, but not to USB MIDI controllers.
The CV output is in the 0 .. 4V range – so a tessitura of 4 octaves is covered. The Midi 2 CV does not support V/Hz conversion; only V/Oct.
The Gate output uses V-trig, has a 5V high level, and a direct polarity (note on = 5V, note off = 0V). Most Eurorack modules use a trigger level below 2.5V and can thus be triggered by the Midi 2 CV. If a module or synth requires a higher level, a level conversion circuit such as the CD4504 can be used. Polarity inversion can be implement with a CD4049 or with a software hack. S-trig conversion can be implement with a few parts.
The Midi 2 CV works optimally with iOS, OS X >= 10.6.3 or Linux kernel >= 2.6. On other operating systems, the messages might be delayed by up to 8ms, causing a very jittery timing!

Installation

The Midi 2 CV can either be mounted in a Eurorack system, or used as a standalone box. In both cases, it does not need any external power source as it is powered by the USB bus. About conversion modes

The Midi 2 CV interprets MIDI messages differently depending on the MIDI channel on which they are received. For example, when receiving messages on MIDI channel 1, it behaves like a monophonic synthesizer and outputs a CV/Gate pair. When receiving messages on MIDI channel 10, it behaves instead like a drum trigger converter and outputs a trigger for 4 drum instruments. Channel 1: Monophonic mode

This mode is enabled when any MIDI message is received on channel 1. The Midi 2 CV behaves like a classic monophonic CV-Gate converter implementing most recent note priority.

OUT 1: Note CV
OUT 2: Velocity CV
GATE 1: Gate
GATE 2: Gate

Channel 2: Turbocharged monophonic mode

This mode is enabled when any MIDI message is received on channel 2. The Midi 2 CV behaves like a monophonic CV-Gate converter implementing most recent note priority, but the primary Gate output is now a digital square oscillator!

OUT 1: Note CV
OUT 2: Velocity CV
GATE 1: Square oscillator playing the received MIDI note
GATE 2: Gate

Bonus digital square oscillator! Hell Yeah! Channel 3 / Channel 4: Dual monophonic mode

This mode is enabled when a MIDI message is received on channel 3 or on channel 4. The Midi 2 CV behaves like two independent monophonic CV-Gate converters with most recent note priority. One of them listens to notes received on channel 3, the other on channel 4.

OUT 1: Note CV for channel 3
OUT 2: Note CV for channel 4
GATE 1: Gate for channel 3
GATE 2: Gate for channel 4

Channel 5: Duophonic mode

This mode is enabled when a MIDI message is received on channel 5. The Midi 2 CV behaves like a duophonic CV-Gate converter with voice stealing.

OUT 1: Note CV output 1
OUT 2: Note CV output 2
GATE 1: Gate
GATE 2: Gate

Channel 6: Controller conversion

This mode is enabled when a MIDI message is received on channel 6. The Midi 2 CV converts continuous controllers (CC) 01 (modulation wheel) and 02 (breath controller) to control voltages.

OUT 1: Modulation wheel CC (01)
OUT 2: Breath controller CC (02)
GATE 1: Binarized value of CC 3
GATE 2: Binarized value of CC 4

Channel 7/8: Note conversion + CC

These modes are enabled when a MIDI message is received on channel 7 or 8. The Midi 2 CV behaves like a monophonic CV-Gate converter, with an additional CC value produced on the secondary output.

OUT 1: Note CV
OUT 2: Modulation wheel or breath controller CC (01 or 02)
GATE 1: Gate
GATE 2: Gate

Channel 10: Drums

This mode is enabled when a MIDI message is received on channel 10. CV Outputs 1 and 2 are respectively triggered by the MIDI notes 36 (kick drum on the GM drum map) and 38 (snare drum on the GM drum map). Gate outputs 1 and 2 are triggered by the MIDI note 40 (snare drum 2) and 46 (closed high-hat).

OUT 1: BD (note 36) trigger
OUT 2: SD (note 38) trigger
GATE 1: SD2 (note 40) trigger
GATE 2: CHH (note 46) trigger

Channel 11: Drums gates

Same as Channel 10, but with gates instead of triggers. Channel 12, 13, 14: Monophonic mode with clock/reset output

In these modes, the Midi 2 CV behaves like a classic monophonic CV-Gate converter implementing most recent note priority, but also outputs triggers for synchronizing modular sequencers. A clock (with variable resolution) is sent to GATE 1; and a reset (corresponding to the MIDI ‘start’ message) is sent to GATE 2.

OUT 1: Note CV
OUT 2: Note Gate
GATE 1: Clock trigger
GATE 2: Reset trigger

The resolution of the clock trigger depends on the MIDI channel used: 24 ppqn for channel 12; 8 ppqn for channel 13; 4 ppqn for channel 14.

The Midi 2 CV is open source hardware The original design for this project is Creative Commons licensed by Olivier Gillet: CC-BY-SA: Attribution / ShareAlike If you decide you would like to use this project in part or whole in your own design, please credit Mutable Instruments and change the logo and name. This license does permit commercial use of these designs, but consider getting in touch with Mutable Instruments before selling anything.

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