NAME

MIDI::Score - MIDI scores

SYNOPSIS

  # it's a long story; see below

DESCRIPTION

This module provides functions to do with MIDI scores. It is used as the basis for all the functions in MIDI::Simple. (Incidentally, MIDI::Opus's draw() method also uses some of the functions in here.)

Whereas the events in a MIDI event structure are items whose timing is expressed in delta-times, the timing of items in a score is expressed as an absolute number of ticks from the track's start time. Moreover, pairs of 'note_on' and 'note_off' events in an event structure are abstracted into a single 'note' item in a score structure.

'note' takes the following form:

 ('note_on', I<start_time>, I<duration>, I<channel>, I<note>, I<velocity>)

The problem that score structures are meant to solve is that 1) people definitely don't think in delta-times -- they think in absolute times or in structures based on that (like 'time from start of measure'); 2) people think in notes, not note_on and note_off events.

So, given this event structure:

 ['text_event', 0, 'www.ely.anglican.org/parishes/camgsm/chimes.html'],
 ['text_event', 0, 'Lord through this hour/ be Thou our guide'],
 ['text_event', 0, 'so, by Thy power/ no foot shall slide'],
 ['patch_change', 0, 1, 8],
 ['note_on', 0, 1, 25, 96],
 ['note_off', 96, 0, 1, 0],
 ['note_on', 0, 1, 29, 96],
 ['note_off', 96, 0, 1, 0],
 ['note_on', 0, 1, 27, 96],
 ['note_off', 96, 0, 1, 0],
 ['note_on', 0, 1, 20, 96],
 ['note_off', 192, 0, 1, 0],
 ['note_on', 0, 1, 25, 96],
 ['note_off', 96, 0, 1, 0],
 ['note_on', 0, 1, 27, 96],
 ['note_off', 96, 0, 1, 0],
 ['note_on', 0, 1, 29, 96],
 ['note_off', 96, 0, 1, 0],
 ['note_on', 0, 1, 25, 96],
 ['note_off', 192, 0, 1, 0],
 ['note_on', 0, 1, 29, 96],
 ['note_off', 96, 0, 1, 0],
 ['note_on', 0, 1, 25, 96],
 ['note_off', 96, 0, 1, 0],
 ['note_on', 0, 1, 27, 96],
 ['note_off', 96, 0, 1, 0],
 ['note_on', 0, 1, 20, 96],
 ['note_off', 192, 0, 1, 0],
 ['note_on', 0, 1, 20, 96],
 ['note_off', 96, 0, 1, 0],
 ['note_on', 0, 1, 27, 96],
 ['note_off', 96, 0, 1, 0],
 ['note_on', 0, 1, 29, 96],
 ['note_off', 96, 0, 1, 0],
 ['note_on', 0, 1, 25, 96],
 ['note_off', 192, 0, 1, 0],

here is the corresponding score structure:

 ['text_event', 0, 'www.ely.anglican.org/parishes/camgsm/chimes.html'],
 ['text_event', 0, 'Lord through this hour/ be Thou our guide'],
 ['text_event', 0, 'so, by Thy power/ no foot shall slide'],
 ['patch_change', 0, 1, 8],
 ['note', 0, 96, 1, 25, 96],
 ['note', 96, 96, 1, 29, 96],
 ['note', 192, 96, 1, 27, 96],
 ['note', 288, 192, 1, 20, 96],
 ['note', 480, 96, 1, 25, 96],
 ['note', 576, 96, 1, 27, 96],
 ['note', 672, 96, 1, 29, 96],
 ['note', 768, 192, 1, 25, 96],
 ['note', 960, 96, 1, 29, 96],
 ['note', 1056, 96, 1, 25, 96],
 ['note', 1152, 96, 1, 27, 96],
 ['note', 1248, 192, 1, 20, 96],
 ['note', 1440, 96, 1, 20, 96],
 ['note', 1536, 96, 1, 27, 96],
 ['note', 1632, 96, 1, 29, 96],
 ['note', 1728, 192, 1, 25, 96]

Note also that scores aren't crucially ordered. So this:

 ['note', 768, 192, 1, 25, 96],
 ['note', 960, 96, 1, 29, 96],
 ['note', 1056, 96, 1, 25, 96],

means the same thing as:

 ['note', 960, 96, 1, 29, 96],
 ['note', 768, 192, 1, 25, 96],
 ['note', 1056, 96, 1, 25, 96],

The only exception to this is in the case of things like:

 ['patch_change', 200,     2, 15],
 ['note',         200, 96, 2, 25, 96],

where two (or more) score items happen at the same time and where one affects the meaning of the other.

WHAT CAN BE IN A SCORE

Besides the new score structure item "note" (covered above), the possible contents of a score structure can be summarized thus: Whatever can appear in an event structure can appear in a score structure, save that its second parameter denotes not a delta-time in ticks, but instead denotes the absolute number of ticks from the start of the track.

To avoid the long periphrase "items in a score structure", I will occasionally refer to items in a score structure as "notes", whether or not they are actually "note" commands. This leaves "event" to unambiguously denote items in an event structure.

These, below, are all the items that can appear in a score. This is basically just a repetition of the table in MIDI::Event, with starttime substituting for dtime -- so refer to MIDI::Event for an explanation of what the data types (like "velocity" or "pitch_wheel"). As far as order, the first items are generally the most important:

('note', starttime, duration, channel, note, velocity)

('key_after_touch', starttime, channel, note, velocity)

('control_change', starttime, channel, controller(0-127), value(0-127))

('patch_change', starttime, channel, patch)

('channel_after_touch', starttime, channel, velocity)

('pitch_wheel_change', starttime, channel, pitch_wheel)

('set_sequence_number', starttime, sequence)

('text_event', starttime, text)

('copyright_text_event', starttime, text)

('track_name', starttime, text)

('instrument_name', starttime, text)

('lyric', starttime, text)

('marker', starttime, text)

('cue_point', starttime, text)

('text_event_08', starttime, text)

('text_event_09', starttime, text)

('text_event_0a', starttime, text)

('text_event_0b', starttime, text)

('text_event_0c', starttime, text)

('text_event_0d', starttime, text)

('text_event_0e', starttime, text)

('text_event_0f', starttime, text)

('end_track', starttime)

('set_tempo', starttime, tempo)

('smpte_offset', starttime, hr, mn, se, fr, ff)

('time_signature', starttime, nn, dd, cc, bb)

('key_signature', starttime, sf, mi)

('sequencer_specific', starttime, raw)

('raw_meta_event', starttime, command(0-255), raw)

('sysex_f0', starttime, raw)

('sysex_f7', starttime, raw)

('song_position', starttime)

('song_select', starttime, song_number)

('tune_request', starttime)

('raw_data', starttime, raw)

FUNCTIONS

This module provides these functions:

$score2_r = MIDI::Score::copy_structure($score_r)

This takes a reference to a score structure, and returns a reference to a copy of it. Example usage:

          @new_score = @{ MIDI::Score::copy_structure( \@old_score ) };
    

$events_r = MIDI::Score::score_r_to_events_r( $score_r )

($events_r, $ticks) = MIDI::Score::score_r_to_events_r( $score_r )

This takes a reference to a score structure, and converts it to an event structure, which it returns a reference to. In list context, also returns a second value, a count of the number of ticks that structure takes to play (i.e., the end-time of the temporally last item).

$score2_r = MIDI::Score::sort_score_r( $score_r)

This takes a reference to a score structure, and returns a reference to a sorted (by time) copy of it. Example usage:

          @sorted_score = @{ MIDI::Score::sort_score_r( \@old_score ) };
    

$score_r = MIDI::Score::events_r_to_score_r( $events_r )

($score_r, $ticks) = MIDI::Score::events_r_to_score_r( $events_r )

This takes a reference to an event structure, converts it to a score structure, which it returns a reference to. If called in list context, also returns a count of the number of ticks that structure takes to play (i.e., the end-time of the temporally last item).

$ticks = MIDI::Score::score_r_time( $score_r )

This takes a reference to a score structure, and returns a count of the number of ticks that structure takes to play (i.e., the end-time of the temporally last item).

MIDI::Score::dump_score( $score_r )

This dumps (via "print") a text representation of the contents of the event structure you pass a reference to.

MIDI::Score::quantize( $score_r )

This takes a reference to a score structure, performs a grid quantize on all events, returning a new score reference with new quantized events. Two parameters to the method are: 'grid': the quantization grid, and 'durations': whether or not to also quantize event durations (default off).

When durations of note events are quantized, they can get 0 duration. These events are not dropped from the returned score, and it is the responsibility of the caller to deal with them.

MIDI::Score::skyline( $score_r )

This takes a reference to a score structure, performs skyline (create a monophonic track by extracting the event with highest pitch at unique onset times) on the score, returning a new score reference. The parameters to the method is: 'clip': whether durations of events are preserved or possibly clipped and modified.

To explain this, consider the following (from Bach 2 part invention no.6 in E major):

     |------e------|-------ds--------|-------d------|...
|****--E-----|-------Fs-------|------Gs-----|...
    

Without duration cliping, the skyline is E, Fs, Gs...

With duration clipping, the skyline is E, e, ds, d..., where the duration of E is clipped to just the * portion above

COPYRIGHT

Copyright (c) 1998-2002 Sean M. Burke. All rights reserved.

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

AUTHORS

Sean M. Burke "sburke@cpan.org" (until 2010)

Darrell Conklin "conklin@cpan.org" (from 2010)