MIDI Magic

During the Lenten Reflection series at St. Andrew’s Presbyterian Church, Southampton I decided to use the MIDI capability of organ. As a follow up I thought it would be useful to explain what is possible with this capability.

As our pipe organs get refurbished and modernised they often get various upgrades, perhaps the most far reaching is the upgrade to the mechanics of the console. In several organs in our area the heart (or perhaps I should say the brain) of the organ has been updated to what amounts to a dedicated computer sitting between the manual, pedal board, stops, etc. and the pipe valves, etc. It is normal now that a MIDI capability will come as part of the upgrade.

MIDI (Musical Instrument Digital Interface) originated in 1981 when several companies developing synthesizers proposed a universal synthesizer interface, this would allow direct communication between equipment from different manufacturers. This was fully standardized in 1983 as the MIDI Standard. The standard has gone through several revisions over the years, but has for a long time been standard on most electronic/digital musical instruments and typically any modern instrument will have a MIDI Out and MIDI In connection. It was decided in the design to use what was a pretty standard connection in the audit industry – the 5 pin DIN connector. It was also designed to allow reasonable cable runs (50 feet) without any problems with signal loss, or interference. As the range of music hardware expanded the range of devices that can support MIDI has grown and is no longer limited to simple keyboards and sound modules.

There are number of levels that MIDI works at. The basic requirement is to be able to send note data between devices. So, for example, a keyboard (a MIDI Controller) can send note information to a sound module, or in our case the organ console. MIDI sends at least two events, a Note On event (when the key is pressed) and a Note Off event (when it is released). The notes are numbered from 0 to 127 (almost 11 octaves) and middle C is note 60, this means we can send data for notes well outside the range of an organ manual, or even a full grand piano.

To allow a MIDI controller, or MIDI data from a computer, to control more than one sound module there are 16 MIDI channels the data can be sent over. Each device that wants to receive data can be set to receive on a specific channel, if it wants to receive all channels it can be set to Omni mode. In the case of the organ each division is typically assigned to a different channel so notes can be sent which ever division you want by sending them on the correct channel. There is actually more data being sent with each note. Most MIDI keyboards will send also velocity data, which relates to hard (quickly) the key is hit, and after-touch data, which relates to how hard the key is pressed after it is down. For the pipe organ there isn’t really anything it can do with this data, so it is ignored.

At Southampton I had a MIDI Keyboard connected to the console and I had the keyboard split at middle C. This meant I could assign notes middle C and above to the Swell and notes below to the Great (by assigning the two parts of the split to different MIDI channels). This meant I could have the MIDI keyboard next to piano and effectively play the piano and organ together.

Another part of the MIDI standard is related to Continuous Controllers (CC). These are things that can generate a stream of data, in our case the main one of interest is the Expression Pedal (CC#11). On my MIDI Keyboard I had an expression pedal connected and assigned this to the Swell MIDI channel, so the console associates this to the swell pedal and I could control the Swell box remotely as well.

MIDI also covers Program Change data. This data is normally used by the MIDI controller to change the sound the sound module is making. Modern modules may have 100’s, or 1000’s of possible sounds available, for example Pianos, Strings, Brass, Synthesizer sounds. If you know what the module is expecting then you can send the right program change data to control it. In the case of the pipe organ this might be used to control stop selection and coupling.

The last set of MIDI data is called System Exclusive (SysEx) data. This is very low level data that is specific to whatever is receiving it and can be used for many things including building new sounds from scratch.

On the console at Southampton each division also has a MIDI stop. This allows the organ to send MIDI data out when the stop is selected. If everything is configured correctly you can then play an external expander/sound unit from the console as well as the normal stops.

Although the keyboard/sound module setup is easy to envisage there are a lot more ways you can generate and use MIDI data and you can even use multiple sources and merge the data together. For example, this would allow you to have 2,3,.. players all playing the organ at the same time, you could also use a PC to play the console, etc. You can send the MIDI out from the console to a sound module, a PC, or another pipe organ. Theoretically if you had reliable internet you could play a piece at Southampton and send the MIDI to simultaneously play the piece as Chesley – you would have to sort the stops out first! You can now also use MIDI wirelessly so the 50’ restriction is no longer an issue. As MIDI data isn’t really a musical notation you can actually send it to things that don’t produce sound (e.g. a light show), as long as the receiver knows how to read the data.

The modern console will normally allow you to record and playback a piece internally. Making the recording via MIDI on a PC means you then have limitless opportunities to edit it in any way you want. You can play it on a totally different organ, or any other instrument, or use a notation program to engrave your latest masterpiece.

If we hold a future meeting at an appropriate venue we could do some practical demos, or even include a section in the upcoming seminars?

Julian Delf