UEE051H3 - Studio Technology - THE MIDI SEQUENCER

UEE051H3 - STUDIO TECHNOLOGY

THE MIDI SEQUENCER

These notes accompany the third lecture in the Principles of Electronic Music Synthesis segment, of the level 3 Studio Technology module UEE051H3. After attending the lecture and reviewing these notes you should:

attain a broad understanding of the role and history of the Sequencer within electronic music synthesis, and
understand the role of the computer-based software MIDI sequencer within Studio Technology, and in particular how it can be used by the synthesist:

as a music composition tool, or
to arrange and playback music sequences stored in Standard MIDI File (SMF) format.

You should also gain an appreciation of the importance of Quantization and Humanization functions within the MIDI sequencer.

For questions, comments or feedback please contact the author Alan Winfield, via:

phone: 0117 976 2534

email: a-winfield@uwe.ac.uk

1. History

In the early days of electronic music synthesis (late 1960s and 1970s) prior to the invention of the MIDI specification, the Sequencer was a hardware device that, when connected to a synthesizer, would automatically play a repeating or looped sequence of notes. At this time synthesizers were analogue devices and the majority relied on the principle of Voltage Control (invented by Robert Moog - the 'father' of the electronic synthesizer). In a Voltage Controlled Analogue Synthesizer, the pitch of the note played is proportional to the applied input voltage (and many synths conformed with the 1Volt/Octave standard). Thus a hardware analogue sequencer needs to produce an output voltage level which step changes, to the appropriate level, at the start of the next 'note' in the sequence, as illustrated in the diagram below:

Output of Hardware Analogue Sequencer

The diagram above shows what the output voltage may look like for an 8 note repeating sequence, although in practice such devices allowed longer sequences of say 12 or 16 notes. There were clearly severe limitations in such sequencers, including:

the limited length of the note sequence,
the restriction to repeating or looped sequences, and
the difficulty of note timing other than completely regular equal length notes.

Despite these limitations the devices were prevalent in early electronic music, producing a characteristic electronic riff. For instance, the use of such a sequencer became the trademark of pioneering German electronic music trio Tangerine Dream in the 1970s. A number of classic analogue monophonic synthesizers incorporated a built-in sequencer, including for instance the Roland SH101.

The software based MIDI sequencers described below bear almost no resemblance to their hardware analogue predecessors, except of course in the name sequencer.

2. The Software MIDI Sequencer

The widespread adoption of the Musical Instrument Digital Interface (MIDI) in the early 1980s opened the way for a wealth of computer based software application for the music studio, but foremost of these is the MIDI sequencer. The software MIDI sequencer is an application which allows multi-part music to be created, edited, stored and played back (via a MIDI interface). In order to visualise this process consider the diagram below.

In the diagram above I have shown the two main elements of the synthesizer as separate, ie the Keyboard and the Synthesizer (sound generating element). These may be physically separate units (and often are), but equally often are sub-systems within a single synthesizer. Of course the controller keyboard may drive the synth hardware directly, as shown in the dotted MIDI connection above, and this configuration would obviously allow the synth to be used as a stage or performance instrument.

However, breaking the direct connection between the keyboard and the synth, and placing a Personal Computer (running a MIDI sequencer) between the two, as shown above, opens up tremendous possibilities for studio composition and playback of multi-part electronic music, far beyond the capabilities of the synthesizer alone. (In fact some synths do have a MIDI sequencer, with editing and storage capabilities, built-in; such synths are often known as 'workstations' to distinguish them from other instruments without MIDI sequencing).

In the configuration illustrated above, the keyboard acts as a MIDI input device, to the sequencer. Sequencer software does, however, generally allow note entry in other ways than by playing the keyboard; for instance by use of a 'notation' editor (to enter notes in musical notation), or a 'piano roll' editor (to enter notes using a simpler 'piano roll' paradigm). Using a MIDI controller keyboard does of course require at least basic keyboard playing skills, but musical composition is still perfectly feasible to those who cannot play keyboards, using the piano roll or notation editors.

2.1 A Generic Specification

Here are the features and facilities that would be expected in any software MIDI sequencer:

The means to assign MIDI channels to individual 'tracks' or 'parts' of the sequence (or composition);
the means to assign individual instruments to each 'track' (using the MIDI program change message);
facilities for at least 16 'tracks' or 'parts';
the ability to enter notes into individual parts, using a 'piano-roll' editor;
the ability to enter notes, in real-time, using a MIDI controller keyboard and the MIDI input port of the PC;
the ability to play back the composition (or sequence) currently in memory as a series of MIDI commands output via the PC's MIDI output port, with accurate timing;
the ability to enter notes from the keyboard (record), whilst simultaneously playing back tracks already entered;
the ability to manipulate note data using cut, paste and other such editing tools, including musically meaningful operations, such as 'transpose key', or 'time shift';
the ability to save or load a complete sequence (or composition) to or from disk in Standard MIDI File (SMF) format;
the means to enter and edit 'musical dynamics' information, ie 'loudness', 'pitch bend', 'pan' etc, in order to add musical expression to the composition;
the means to 'quantise' a sequence (that is, 'correct' any timing inaccuracies), to a given resolution, and its converse,
the means to 'humanize' a sequence (that is add 'random' timing variations, in order to add a 'human' feel), to a given resolution.

Additional features that might be found on more sophisticated sequencers would include:

A 'notation editor', so that tracks may be viewed, and edited, using correct musical notation, and printed as part of a 'score';
a 'drum editor' to provide a more meaningful user interface for entering drum patterns than is provided by either the piano-roll or notation editors;
the means to manipulate raw MIDI command data, and especially, to be able to incorporate properly formatted MIDI 'System Exclusive' messages;
a graphical 'mixing desk' which allows the level, balance and other parameters for each track to be individually set, and varied during playback.

It should be clear from the above that MIDI sequencers are sophisticated and non-trivial applications. At the professional end of the spectrum they are extremely powerful (and relatively costly) applications which can, quite literally, form the 'nerve centre' of a music studio (or as part of a stage setup for some musicians). Less featured MIDI sequencers are, however, well within the reach of amateur musicians and perfectly capable sequencers can even be found as shareware offerings via the internet.

3. The MIDI Sequencer: A Guided Tour

4. MIDI Sequencer Software: Links to Internet Resources

Passport Designs: http://www.passportdesigns.com/
Steinberg International: http://www.steinberg-us.com/
Evolution Music: http://www.evolution-uk.com/

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