MIDI

MIDI (short for Musical Instrument Digital Interface) is a communications protocol/digital interface that allows a wide variety of computer devices to connect and communicate with one another. In theatre, it is usually used as a method of remote controlling one piece of equipment from another.

These days, MIDI is getting a bit long in the tooth and is largely being replaced by OSC as a much better and more versatile option for remotely controlling devices and technical equipment. Though QLab and the lighting desks now in use at the ADC Theatre and Corpus Playroom support OSC, the remainder of this page serves as a useful historical reference for devices that do not.

Remote control

MIDI Show Control (MSC) can be used for remote control. The two devices that are likely the most ubiquitous for use in this way in the theatre world are EOS-based lighting desks and QLab.

QLab controlling EOS

In order for this to work, 'MSC Receive' must be turned on for the show file on the LX desk. To do this, open the browser, navigate to 'Show Setup', then click 'Show Control'. Ensure 'MSC Receive' is enabled, and select an arbitrary value between 0 and 15 for the 'MSC Receive Channel' (it may be a good idea to select a different channel for the mainshow and lateshow to avoid the wrong cues firing). To create a cue which triggers a lighting cue, create an 'MSC' cue in QLab. The most important value is the 'Q Number', which corresponds to the number of the cue on the lighting desk which you wish to trigger. The other options are:

Output Patch: corresponds to which MIDI patch to use in QLab.
Command Format: selects which sort of equipment (e.g. lighting, sound, projection) should respond to the cue. The EOS software responds to 'All Types'.
Command: 'GO' is the most often used.
Device ID: This must correspond to the 'MSC Receive Channel' selected on the LX show file.
Q List: blank by default, which causes the active cue list to be used.
Q Path: This is part of the MSC spec, but isn't believed to be used by EOS software.

EOS controlling QLab

This is useful if the show has lighting ops and only a few sound cues. An LX desk can be configured to transmit an MSC 'Go' command whenever the active cue is changed (e.g. by pressing 'Go', 'Stop/Back', 'Go to cue', but not with follow-ons). To do this, 'MSC Transmit' must be turned on for the show file. Open the browser, navigate to 'Show Setup', then click 'Show Control'. Ensure 'MSC Transmit' is enabled, and select an arbitrary value between 0 and 15 for the 'MSC Transmit Channel'.

In the QLab file, open the preferences and click 'Remote Control' on the left. Ensure that 'Use MIDI Show Control' is checked and that 'Use Device ID' matches the 'MSC Transmit Channel' selected above. Give all cues in Qlab and cue number corresponding to a cue number on the Ion. You will probably end up having to create dummy lighting cues which do not change the lighting state specifically to trigger QLab cues.

Controlling other devices

Being old, a large number of lighting desks feature support for MSC and have 8-pin DIN connector ports to route the control signals.

The Zero88 Jester, perhaps the most common low-end lighting desk and the one used in the ADC's Larkum Studio, supports MIDI.
There's an infamous out-by-one difference with MIDI messages, including with MSC channel numbers/device ids, caused by some devices starting at 1 and others at 0. Both QLab and the ETC Ion use numbers starting from zero, but if something isn't working, try adding/subtracting one.
A wide variety of devices (e.g. sound equipment and keyboards) can be controlled using other types of MIDI messages (e.g. Note On/Off, Program Change, Control Change, SysEx), all of which are supported by QLab (using 'MIDI' or 'MIDI SysEx' cues instead of 'MSC' cues). The exact implemention varies from device to device, and the best source of information is usually the instruction manual.
One computer running QLab can be made to control another computer running QLab, which may be useful on a particularly complicated show. MacOS has built-in support for sending MIDI over a network, which may be useful for these sorts of setups.

Transmitting MIDI over longer distances

If you wish to transmit MIDI signals over longer distances at the ADC (e.g. to the SM desk or plot desk), the audio tie lines and patch system can be used. At the time of writing, the ADC has 3 adapters (one-and-a-half pairs) to convert between MIDI and XLR connections at either end, which are kept in the bottom sound drawer.