skills/musical/references/notation.md

# Notation

Rules for any exercise that writes rhythm down, and for checking rhythm the
learner has written. These are strict - a bar that breaks them is wrong, not a
stylistic variant.

## Bars must add up exactly

Every bar contains notes and rests summing to exactly the number of beats the
time signature specifies. In 4/4 that is exactly 4 beats: not 3.5, not 4.5.

Check this by arithmetic, every time, before looking at anything else about the
bar. Note values in beats, in 4/4:

| Note | Beats |
|---|---|
| Whole | 4 |
| Dotted half | 3 |
| Half | 2 |
| Dotted quarter | 1.5 |
| Quarter | 1 |
| Dotted eighth | 0.75 |
| Eighth | 0.5 |
| Sixteenth | 0.25 |

A dot adds half the note's value. A tie adds the two values together and may
cross a barline; a dot may not.

The lower number of the time signature says which note value gets one beat: 4
means a quarter note, 8 means an eighth note, 2 means a half note. In 6/8 there
are six eighth-note beats, usually felt as two groups of three.

## Beaming

Eighth notes and shorter must be beamed together in groups that add up to
**one beat**.

In 4/4 that means beams group within each quarter-note beat: four sixteenths
beamed as one group, two eighths beamed as one group, an eighth plus two
sixteenths beamed as one group.

## Beams must not cross the midpoint of the bar

This overrides the one-beat grouping rule where they conflict.

In 4/4 the midpoint falls between beat 2 and beat 3 - beats 1 and 2 are the
first half, beats 3 and 4 the second. A beam group may not span from the first
half into the second. An eighth note on beat 2.5 must not be beamed to an eighth
note on beat 3; break the beam there and start a new group.

The purpose is that a reader can see the halves of the bar at a glance. A beam
that hides the midpoint makes the bar harder to read even when the arithmetic is
correct.

In 6/8 and other compound meters the equivalent division is between the two
dotted-quarter groups: do not beam across it.

## Checking written rhythm

In order:

1. Sum the bar. If it does not equal the time signature exactly, stop - that is
   the error, and nothing else matters yet.
2. Check every beamed group sums to one beat.
3. Check no beam crosses the midpoint.
4. Only then comment on anything else.

Report the first failure you find rather than all three at once. A learner whose
bar has five beats does not need beaming advice yet.