Confusion with identifying the bottom number of the time signature of a song by ear

Question

I have some confusion about identifying the bottom number of the time signature by ear when listening to songs. I'll use two examples to illustrate my confusion, one in simple meter and one in compound meter. My question is the same for each of the two examples. I just thought to use two different examples to drive the point home.

1. Example 1: Let's take the verse that comes after the intro verse of the song Under the Bridge by the Red Hot Chili Peppers (in the video below see 0:58-1:22)
   From looking online I know that this verse is in 4/4 time (i.e., 4 beats per bar where each beat is a quarter note). Here's my confusion. So, when doing this by ear and feeling out the pulse I can easily say there is a repeating 1-2-3-4 pulse going on here. So I can say the that there are 4 beats per bar here. So it makes sense why the top number of the time signature is a 4. But my confusion then is about why the note that gets the beat is necessarily a quarter note? Why couldn't it be a half note or eighth note or any or any other type of note? I understand the difference between a whole note, half note, quarter note, eighth note, and so on... a whole note = 2 half notes, 4 quarter notes, 8 eighth notes, and so on... But that still doesn't tell me how we know to use a quarter note per beat in the song.
2. Example 2: Let's take the verses of the song Norwegian Wood, by the Beatles (see 0:00-0:32 in the video below)
   From looking online I know that this verse is in 6/8 time (i.e., 2 beats per bar where each beat is a dotted quarter note). So I can clearly hear a repeating 1-2-3-4-5-6 pulse here. But clearly pulses 1 and 4 are the accented/strong pulses and the other pulses are weak... and so it makes sense that we have 2 beats per bar, where each beat counts are 3 pulses. So it makes sense why the top number of the time signature is a 6. But my confusion then is about why the note that gets the beat is necessarily an eighth note? Why couldn't it be a half note or quarter note or any or type of note? As with the last example, I understand the difference between a whole note, half note, quarter note, eighth note, and so on... But that still doesn't tell me how we know to use a quarter note per beat in the song.

Thanks.

Answer 1

Identifying the denominator of a time signature by ear is impossible because it's arbitrary. It's a decision on part of the transcriber to which note value they map a beat.

There are tendencies and customs, though. A four-beat time will probably be written as 4/4, rather than 4/8 or 4/2. You aren't very likely to come across 6/4 or 6/16, it'll be 6/8 instead. And if an unusual choice turns up, it tends to pair with an unusual tempo - such as, a very fast waltz written as 3/8 rather than 3/4.

Answer 2

How do you identify the "bottom number" of a time signature just by listening? Short answer: You can't. Meter is an idea, not really something you can hear. Yes, downbeats are often emphasized, but not always or extremely (that would sound kinda dumb). Really, meter is just a concept around which the "real music"—pitches and durations—is organized. The long answer is that you can make some educated guesses based on common practice.

These passages would all sound identical:

Theoretically, if you heard this without seeing it, there's no way to know which it is. However, 4/4 is much more common. You don't usually see the others unless there's some good reason for them. (Like, maybe you would choose 4/2 if there were many smaller notes coming, and you wanted the music to be less cluttered by beams. Or, more often, you encounter 4/2 in renaissance music because half notes used to be the default value.)

Similarly, 6/8 could technically be written as 2/4 with constant triplets. These would sound the same:

... but 6/8 exists just so you don't have to write all those triplets. It would be the more reasonable choice. But if your music was mostly duples with the occasional triplet, 2/4 would make more sense. And if it fluctuated frequently between the two, you'd have to pick one.

And that's what it comes down to. If you're writing your own music, you often have to scratch your head about what's the best way to notate your rhythm, but you pick one and go with it. If you're transcribing, then maybe you can reference some original, or else... you make the same choices.

Answer 3

Time signatures are cultural conventions, not a laboratory measurement of a physical phenomenon. Music is culture, and music theory belongs to humanistic sciences, not natural sciences like mathematics or physics.

When is something "half-time"? When do you use 2/4 instead of 4/4? When is it 4/4 with triplets vs 6/8 vs 12/8? Sounds like 16th beat, but maybe the authors were thinking of very fast 8th beat instead, 200 bpm of 1/8th instead of 100 bpm 1/16th? You need to identify the genre and cultural background of the music, and then make an educated guess at how people of that culture would have notated it. If they use notation at all. You could even decide to ignore the cultural conventions and write it in a way that you think makes sense for your own particular purpose.

Why do you want to notate or transcribe the music - who is your target audience, and what are you trying to communicate with the written notation?

To get familiar with the various cultural conventions, you'll have to read music and gradually accumulate cultural knowledge.

Answer 4

why the note that gets the beat is necessarily an eighth note? Why couldn't it be a half note or quarter note or any or type of note?

It could. We can be fairly definite about how many beats are in a bar, and whether they're simple or compound beats. But e.g. 'simple duple' can be written as 2/4 or in 'cut-common', and there's nothing to say which choice is 'correct'.

OK, convention comes into it. An old-style military march was generally notated in 2/4, the modern tendency leans towards 'cut-common'. 2/8 or 2/16 are theoretically possible, but would be very unusual!

Answer 5

First, let's think about the specifics of writing in x/1. While you would use the least amount of ink (whole notes have no stems, whole and half notes are hollow, quarter notes have no flags, etc...) you would also provide the smallest number of extra cues for musicians who may have vision challenges. Musical conventions were codified during a time when human vision went largely uncorrected. Hollow notes are harder to see, stems should be exactly one octave in length, and the flags provide an additional visual cue for musicians. When sight-reading, the performer has more time to examine whole and half notes by virtue of their duration. To fill a measure in x/1 time, you'd have to resort either to slurring whole-notes together or to longas and breves which have become rare and are also difficult to visually parse.

Conversely, if you wrote in x/64, the "beat notes" would each get 4 flags. When humans have to count over 3, they resort to either explicit counting or groupings because we aren't hard-wired to see 4 and say 4 as fast as we see 2 and say 2. In fact, when sight-reading 64th notes, musicians often just ignore the upper flags and go by the differences on the note-side of the flags. All that extra ink and the time it took to put it on the page would need to add value, and it usually doesn't.

Between these two factors, we have a preference for notes between half and sixteenth in duration which goes a long way to deciding the time signature. Some of this is moot in an era of corrected vision, but those conventions remain, so we can focus on denominators between 2 and 8.

Next, let's think about time signatures with odd numerators like 5/4. Why choose 5/4 over 5/2 or 5/8? From a purist's perspective, there's no difference between these time-signatures, but we usually choose 5/4 or if it's got 8th note syncopation, 10/8. While there are thousands of examples of both long sixteenth notes and short half notes, it's valuable for composers to work within conventions. Why add un-needed barriers for your musicians to fight through?