But not entirely arbitrary

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

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 genre's of music is to deliberately turn previously established conventions on their head. For instance in jazz there are a lot of syncopated rythms. 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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