Q: I'm sure you've gotten this question before but I don't understand the difference between 3/4 and 6/8 (time signatures)? Is it just the triplets? People (music teachers) always seem to emphasize how it's important that we know they're different but they never actually explain what the difference is.
A: a mathematical guideline for time signatures, supposedly, is that the top number is how many beats per bar, and the bottom number is what note is a beat. So, by that logic, 2/4 means 2 beats per bar, and a 4th note (quarter note) gets 1 beat. By the same logic, 7/2 (as if anyone ever uses that, which they don't) would mean 7 beats per bar, and a Half note gets one beat. But, here's the thing: usually, in actual reality, when the bottom number is 8, the eighth notes are usually going by too fast to actually 'feel' like a beat. But by the sheer logic of the 'beats' rule as described earlier, 6/8 *would* mean, 6 beats per bar, and the 8th note gets one beat. But, almost always, in actual reality, 6/8 is actually fast enough that it's actually felt as if the dotted quarter note gets the beat. So that would make it 2 beats per bar, and 3 8th notes per beat. So really, to properly follow the system, that would mean your top number should be 2, and the bottom number should be...um.... some kind of decimal (let me perform some calculations)... the bottom number would have to be about 2.6667. So really, in actually reality, the way 6/8 is usually felt, it should more accurately be called 2/2.667. But that would cause chaos all over society, so it's not written that way. But getting back to the difference between 3/4 and 6/8-- if you set your metronome to 120bpm, and count in groups of 3 clicks, let's say that's 3/4 at ♩=120. Now set the metronome to 80bpm, and count in groups of 2 clicks, and subdivide each beat into 3, so like imagine you are counting 8th note triplets in 2/4. 3 triplets per beat, 2 beats per bar. but, plot twist, imagine the small notes are actually 8th notes, and you are living in a universe where there is 3 8th notes per beat, and each beat is a dotted quarter note. This is what it would feel like to be in 6/8, and the tempo marking would be ♩. = 80. In 6/8 (or 12/8) the tempo marking is often marked in terms of a dotted quarter note. So anyway, to conclude, this is not written in any 'rule', but this is just the way it is in the real world -- 6/8, 12/8, and often 9/8, are counted as if the beat is happening on dotted quarter notes. again, the reason being that no one wants to write 2/2.667. And, you may be thinking, why not just put the song in 2/4 and use triplets, or maybe just 4/4, and use triplets. And this is a valid argument, and like i always say, when you are faced with a song with some kind of triplet or quick 3 feel, you just have to ask yourself whether you would prefer to be writing a lot of dots (for all the 'regular' beats which will have to be dotted) OR a lot of the number 3 (for all the triplets). It's a personal decision, and the more you get out there and see the kind of charts that are circulating in your world or community, you can make the decision based on what you think would be most familiar to your reader(s)