It's still important to know the rules and why they exist before you can go break them.

I also noticed the flaw in my argument, I should've said 6/4 is closer to 6/8, instead of going to 3/8. I'll just keep it at that, I admit my wrong. 6/4 is only sometimes 3/4, sometimes it's 2/4, sometimes it's 4/4 and 2/4, but it is practically identical to 6/8, just with notes being twice as long and tempo twice as fast.

I don't know if somebody allready post it, but this is cool (and free)
https//gumroad.com/l/tldrmusic

I feel no shame.

Anyway, the point I'm making is that the notation of the meter and the resulting aural experience are not as strongly tied together in practice. So, the notation is an inadequate definition of meter. Subversion in an artistic sense is irrelevant here. Subverting the notation does nothing to music in this case. Notation ≠ music.

neeeeeeerrrrrrrrrrrrrds

It's dependent upon tempo, sure. But that doesn't change the structure of the metres under discussion. As I said, subverting those structures is entirely up to the person making the music. Of course people are going to NOT adhere to those structures (and then consider how one might conduct those subversive structures!), imagine how boring music would be if everybody wrote in accordance to these time signatures.

Given the topic of the thread, however, I stand by everything I said and my disagreement with Devieus on the interchangeability of the metres.

To vinpous & Devieus:
While some theory books do suggest a convention of 3/4 being 3 impulses and 3/8 being one, in practice it hasn't been consistently adhered to that consistently in the literature (the classic Beethoven 9 Scherzo example comes to mind). Where the aural equivalence between 3/4 and 6/8 would lie would be in 3/4 with 2 bar hypermeter at twice the tempo of the 6/8, but not when the span of 3/4 is the same as that of the 6/8 bar, then they are not equivalent. The the hyper meter and the compound meter are only notationally different. There are some who will make the claim that the different notations would yield different performances, but that's edging into the territory of pseudo-science.

Then there's all the fun of hemiolas and polymeters (multiple perceived meters). Then metrical dissonance. Then Brahms. Some stuff in between. Then Ferneyhough broke music (in a good way). And now? The Python, Lilypond and LaTex don't want to play nice and give me my damn A1 sized score in 21 different meters at once. Bleh. Sod it, I'll just curl up and Netflix all the old shows I loved as a teenager because life's all too hard.

But seriously, this paper might be of interest:
Cohn, Richard, Theory of Musical Meter, November 2015, Yale University/University of Sydney
if you can get ahold of it... I might still have a copy somewhere.

It provides a pretty good first principles definition of meter and pretty good way of thinking about it, though limited after a certain point (damn it Ferneyhough), it could be useful within the scope of this discussion. What's nice about it is that it shifts the focus towards the aurally perceived time events.

I see what you're saying, it took me a while until someone pointed out this song, one inherently in 6/8 for very specific reasons, mixing the 2 and 3 pulses into one, making transcribing into 3/4 impossible; I feel this is only a thing if you do combine them, unless you specifically want the second pulse to be less strong than the first.

No it's not.

3/8 has ONE impulse (it's the same as 1/4 time with a triplet instead of a duplet), 6/8 has TWO impulses (the same as 2/4 with triplets instead of duplets), 9/8 has THREE, 12/8 has FOUR, etc.

1/4 has ONE impulse, 2/4 has TWO impulses, 3/4 has THREE impulses, and so on.

The technicality is that you can subvert those all you want, but that doesn't make a single bar of 6/8 the same as two bars of 3/8 or 3/4.

That's just a technicality. Imagine splitting the bar in half and pretend it's 3/8, then double the note length and half the tempo, you get 3/4. There might be some arcane reason why things don't work that way, but in practice things tend to fall into place either way. One example of which would be a waltz, where every other bar is tapped differently, but still in 3/4.

Awesome, thanks everyone! This helps a lot!

Just a minor addendum to some of the above posts: there is a BIG difference between 6/8 and 3/4. 3/4 has 3x evenly spaced crotchet beats (and is thus a TRIPLE metre), 6/8 has TWO evenly spaced DOTTED CROTCHET beats, making it a DUPLE metre.

You count them like this (the capitals are the emphasis or "down" beat):

3/4 | ONE two three | ONE two three | ONE two three | ...

6/8 | ONE two three FOUR five six | ONE two three FOUR five six | ...

So from that perspective, 3/4 is actually more closely related to 9/8 than to 6/8, because 9/8 has THREE groups of (three) quavers per bar.

9/8 | ONE two three FOUR five six SEVEN eight nine | ONE two three FOUR five six SEVEN eight nine | ...

If you are looking to invest some more time here are some resources that I would recommend, as I am learning music theory from the ground up as well!

Free music theory video lessons:
https://www.youtube.com/user/Lypur

An incredible book/e-book that I purchased and am going through:
http://www.edly.com/mtfpp.html

Those are called time signatures.

The first number tells you how many beats are in the measure.
The second number is usually 2, 4, 8, or 16. It tells you the which note length to count as a beat. If the number is 4, then a quarter note is the "beat unit".

6/8 means there are 6 eighth notes.
4/4 means there are 4 quarter notes.

This denotes a total value of beat units for your measures, so there are a lot of combinations that add to that total.
Because 6/8 has 6 eighth notes total, a measure might have 3 quarter notes.

Or 1 quarter note and 4 eighth notes. It just needs to add up to the total as described in the time signature. The music will sound stronger if notes fall evenly with the beat units, and if there is a repeating pattern in the rhythm.

A few more examples...

2/4 means there are 2 quarter notes
3/4 means there are 3 quarter notes
9/8 means there are 9 eighth notes
12/16 means there are 12 sixteenth notes

It literally means what it is. 4/4, or four quarters, means a bar is comprised of four quarter notes, or at least the notes in the bar have to fill up to that number; it can also be filled by eight eighths, because two eights make one quarter and 8/2=4 quarters in the bar.

That's only half the story, 4/x specifically means that the bar has 4 beats, but x/4 means that a beat is a quarter note, so a 4/8 means a bar is made of four eighths, because an eighth is a beat and there's four beats in a bar. Naturally this means 6/8 means that a bar would need six eighths (there's also very little difference between a 3/4 and a 6/8).

By that token it's also possible to compose in 1/1, a bar has one beat, one beat is one whole note; it's uncommon to use it though, because for timekeeping sake it's easier to tap four times with your feet to make a bar as you play.

Finally, you'll possibly come across 5/4, 7/4 and my favorite, 3,5/4 (which some heathens call 7/8 because they claim you can't have fractures in the signature), these mean that there are 5 quarters in a bar, 7 quarters in a bar, and 3,5 quarters in a bar (3 quarters and an eighth) respectively; one example of 7/4 is 1.75 in C major, tap your feet to the beat and you'll notice it isn't 4/4, the bar seems to alternate between 3 beats and 4 beats; an example of 5/4 is the Gorillaz song 5/4, where it alternates between 2 beats and 3 beats

What do terms like 6/8 and 4/4 actually mean in terms of composing music? When I read music for the pipes, I look at the 6/8 and the 4/4 and I know how it affects the sound of the music in context, but I don't know what it actually means. How does it affect how many notes are in a bar and whatnot?