MIDI, or 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.
When to use MIDI
It is often useful to connect QLab to other devices in the theatre (e.g. the sound and lighting desks) in order to automate cues and reduce the number of operators required. Common scenarios include:
- A mainshow wants to avoid stitching a sound op for each performance, so links QLab to the lighting desk, so that when the lighting cue Go's into certain cues, the sound effects are automatically triggered.
- A complex musical might have a similar set-up above so that the sound op can concentrate on the sound re-enforcement without having to pay attention to cues.
- A complex touring show, which is performing the same set of cues at multiple venues, creates a QLab file which contains MSC (MIDI show control) cues, which remotely control whatever lighting desk is present at each venue.
- A lateshow, with a very small technical team, creates a QLab show file which contains audio cues and MSC cues, and QLab is run from a laptop on the stage manager's desk with no additional ops.
- A show has a sequence of lighting and sound effects that must be precisely synchronised (e.g. a lightning effect).
QLab controlling the ETC Ion
In order for this to work 'MSC Receive' must be turned on for the show file on the Ion. 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 on the Ion, create an 'MSC' cue. The most important value is the 'Q Number', which corresponds to the cue number on the Ion you wish to trigger. The other options are:
- Output Patch: corresponds to the 'patch' number used in the previous paragraph (i.e. 1)
- Command Format: selects which sort of equipment (e.g. lighting, sound, projection) should respond to the cue. The Ion responds to 'All Types'.
- Command: 'GO' most often used. For other commands, see below.
- Device ID: This must correspond to the 'MSC Receive Channel' selected on the Ion.
- Q List: blank by default, which causes the active cue list to be used
- Q Path: This is part of the MSC spec, but I don't think the Ion uses this
ETC Ion controlling QLab
This is useful if the show has lighting ops and only a few sound cues. The Ion can be configured to transmit an MSC 'Go' command whenever the active cue is changed on the Ion (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
MSC is a fairly old standard, and therefore a surprising number of lighting desks have MIDI ports and support it.
- The Jester which is in the Larkum Studio and the Corpus Playroom supports MIDI, but many older desks don't.
- 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.