A small division within the music of a useful size.

It's semi-arbitrary. In a song where the chords change regularly and evenly, they often correspond with a bar, a bit less often two bars or half a bar. Is usually makes up 4 notes of the "normal" length for that piece, but this is not adhered to as time signatures can be any size. But 4 is typical. A march is 4/4 (literally, four quarter notes per bar). A waltz is 3/4 (three quarter notes).

The "normal" note length depends on how the melody is written. Something like Beethoven's fifth has an overwhelmingly majority of notes all the same length (a quarter note). Something from Madonna will have a much wider variation of note lengths.

Bars are often grouped, though there's no notation for that. A song phrase (e.g. a single 'line') will often be 4 or 8 bars. A song section, say, a verse or a chorus, will often have a multiple of four bars - e.g. 12, 16, 20, etc. A 'long' note or a pause at the end of a chorus, for example, is likely to be an extra bar. You can sometimes feel the rhythm of the song take a double-step when that happens.

It's quite tricky to explain if you don't read music. :-)

Wade, who is a muso, if you hadn't realized.

Traditionally the strongest beat is the first in a bar. Arranged from strongest to weakest, in normal 4/4 time the peaks are at notes 1, 3, 2 and 4. In 3/4 time the peaks are 1, 2, and 3, with 2 and 3 about the same strength. Think "waltz". In 2/2 time those strong peaks from 4/4 time are even. In 8/8 time every 8'th peak is stronger. And so on.

People don't, of course, religiously stick to that. But that's the trend, so an experienced musician can hear the difference between 2/2, 4/4 and 8/8 even though they are theoretically different ways of writing the same thing.

Note that I said "traditionally". One common trend for new genres of music is to deliberately turn previously established conventions on their head. For instance in jazz there are a lot of syncopated rhythms. All that syncopated means is that the emphasis is where you don't expect it to be. So 4/4 in jazz is likely to see peaks at 2, 4, 1 and then 3. So the beat is off from where you'd expect it.

So who would notice? It turns out that virtually everyone does! It may take a musician to tell you what's different, but you know that something is as soon as you hear it. (Note, even though the emphasis is wrong, you can still locate the chords because that's where words tend to start, instruments come in, etc. A lot of boundaries in the music line up along chord boundaries, so you get lots of audible reminders that you're "off".)

Cheers,
Ben

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