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Nuts'n bolts of MIDI-CV/Gate conversion
DOEPFER
4. Nuts and bolts of MIDI to CV/Gate conversion
As you may certainly know, synthesizers from the early days of electronic music (1970s and early 1980s)
used so-called „analog" sound generators. Oscillators, filters, and amplifiers generated and processed
sound while parameters as pitch, timbre, and volume were controlled by analog voltages. The voltage that
controls pitch is usually generated by the instrument's keyboard: The further up the keyboard, the higher
the control-voltage and thus the higher the pitch of the note generated by the oscillator. Easy as that.
The loudness contour of an analog synthesizer is generated by an envelope generator. This requires a
certain signal to get it started, the "gate" or "trigger" which is also generated by the keyboard. To make a
long story short: To make an analog synthesizer produce a sound (in the most simple case), a control
voltage to determine pitch, and a gate signal to fire off some tone, are required.
When MIDI came up, the technology to control a synthesizer with changed completely. MIDI transmits
pitch, loudness, note-on, and note-off information as digital data (plus some additional stuff as well).
To connect both worlds – i. e. the integration of a classic analog synthesizer into a contemporary MIDI-
based setup – we need a converter that translates digital data into analog voltages. This is exactly what
Dark Link does.
In those days of yore (see above), not all specifications were subject to technical standards. Some manu-
facturers opted for their own designs. Due to these idiosyncracies, some of the most sought-after vintage
synthesizers have different specifications in terms of controlling pitch and firing off envelope generators.
You ought to keep this in mind when using them in connection with a MIDI to CV/Gate interface.
Voltage control of pitch / scaling
With most analog synthesizers, increasing the voltage controlling pitch by one volt means increasing pitch
by one octave. This so-called volt/octave scaling has since become a common standard and is still valid for
contemporary analog synthesizers. Doepfer´s A-100 modular system and the Doepfer compact synthesizer
Dark Energy also use this standard. That is why Dark Link makes use of it as well. Alas, a handful of
vintage synthesizers (e.g. Korg MS-models and Yamaha CS-models) make use of different types of
scaling, thus cannot be played tonally in combination with Dark Link.
On most analog synthesizers the input socket for controlling pitch externally is labeled "KBD in", "VCO CV
in", „KEY Volt in", "Oscillator CV in" or something along these lines. Plug Dark Link´s CV1 into this input.
Gate
There are also different ways of getting the envelope generators of some synthesizers going. The most
commonly used standard is a positive gate signal, i. e. a positive voltage when a key is held down and zero
volts when no key is depressed. Nearly all manufacturers of now classic synthesizers made use of that
system, e.g. Roland, ARP, Oberheim, Sequential, you name it. If your synthesizer is one of the rare breed
that works in a reversed way (a positive voltage when no key is pressed and zero volts when a key is
depressed), Dark Link can be set up to match this as well (see page 12, note (4)). If that is no good news,
we honestly do not know what is.
The is also no commen standard concerning the level of the gate signals on vintage synths. Some
manufacturers used voltages around 5 V, others 10-12V. Again – Dark Link is prepared: Simply set an
internal jumper to adapt the gate-voltage setting to your needs. Please refer to page 15/16 of this manual.
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