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Page updated: 3-Feb-2012

Sequetron Operation

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Sequetron is a MIDI processing system for converting any MIDI-based source, such as a music keyboard, drum pads etc., into a live multi-track recording & playback system. It intercepts MIDI messages from the input device & interprets them using a special command syntax to dynamically alter its behaviour. This provides the musician with a rich & extendible set of commands for switching between live playing, recording & control, all from the same instrument without ever needing to touch the computer keyboard or mouse. This reduces distractions to creativity & inspiration normally encountered when using musical instruments with computers.

The command set includes sequencer-like functions such as recording, playback, looping, adjusting MIDI attributes etc., but the operation is fundamentally different from conventional programs which dedicate specific music keys to mimic windows control functions. Sequetron's command syntax enables the same music keys to perform multiple functions and, together with a flexible mapping system, allows a practical set of controls even on size-limited devices such as single-octave keyboards and drum pads etc.



This summary uses a keyboard to demonstrate the operation, but any device capable of generating MIDI note events can be used, including drum pads, MIDI controllers, MIDI guitars etc. The term key-press refers to a MIDI note-on event from any of these devices.

The default action is to pass all key-presses straight through to the output device; this is called live play mode. To do anything else requires a special sequence of key-presses known as a command sequence. Its syntax is designed to be logical & consistent for ease of learning, at the same time providing a rich & extendible command set using as few key-presses as possible. All steps of the command sequence are triggered by note-on events so keys do not have to be released before pressing the next. The command sequence terminates automatically when sufficient key-presses have occurred so no additional 'enter' key-press is required.

The 128 possible MIDI key-presses are first mapped to functions according to the user's preference & playing style. These functions are mode-dependent, but modes can overlap for convenience or to use fewer keys/notes on the instrument.

In live play mode, the majority of key-presses are typically mapped to the 'live play' function, so the instrument plays as normal. This diagram shows an example of two octaves mapped for this mode; the playable keys are labelled 'p'.
Example key maps for live mode

A command sequence is initiated when the key corresponding to the 'command' function is pressed, shown above mapped onto the left-most 'C' key and labelled 'cmd'. This causes a switch to command mode, shown below, where the same keys now behave differently.
Example key maps in command mode

Subsequent key-presses are now interpreted as sequence-select functions (Sequetron uses the term 'sequence' instead of 'track', so they are labelled above as 'seq 1', 'seq 2' etc.) and/or a specific command. The optional seq-select functions act as toggles and can be set/reset in any order, but once a key corresponding to a command is pressed, the selection & command are committed and the mode terminates.

If the command requires no further data, it is queued for action on the selected sequences, and the system returns to live play mode, otherwise it switches to value mode where subsequent key-presses are now interpreted as qualifiers for the command.

e.g.1. a change-tempo command expects a beats-per-minute value, so the key functions change to numbers.
Example key maps in tempo mode

e.g.2. a pitch command expects a pitch offset value, so the key functions change to +/- semi-tone offsets relative to the original pitch.
Example key maps in pitch mode

When the correct number of values has been received, the command & values are queued for action on the selected sequences, and the system returns to live play mode.

e.g.3. a record command expects recordable notes and controls for stopping and/or immediately playing back the recording.
Example key maps in record mode

Keys labelled 'r' are recordable; other functions control how the recording is to be stopped. Functions available include a simple stop (for manual playback later), stop & playback immediately, stop & playback automatically after a specific time, etc. The system returns automatically to live play mode when the recording has stopped.

At any stage, the 'esc' function can be pressed to abort the command and return immediately to live play mode.

The musician can play the instrument live, whilst switching in & out of command mode to control the multi-track recorder with minimal interruption.

These videos show the general recording and playback technique in practice, and these show Sequetron's versatility with different MIDI devices: miniature 2-octave keyboard (Yamaha QY-100), drum pads (Korg padKontrol & Yamaha DD14).