Musical theory - pretty much all of it, especially the concept of the “Key.” I can hear that there is a difference between a song played in one key and the same song played in another, but I have only the vaguest idea why it’s in a given key or not.
Since high school, it has always been trigonometry. I am good with numbers and excellent at geometry since I use it almost daily but I can’t grok trig!
Whenever someone explains it again , I slap my head and think “Oh that makes perfect sense!” but I guess as I get older I can’t keep it in there!
The Obvious Topic.
Okay…I don’t get it.
Time signatures in music:
The top number of the fraction are how many beats make up a measure. The bottom number is what kind of note gets a beat. It’s all based of the European music standard of 4/4 - four beats per measure, and each beat is a quarter note (because four quarters is one whole measure).
Under normal circumstances, an eighth note would be one half of a beat. You count it like Lawrence Welk: “One-anna-two-anna-three-anna-four-anna”. But, if your time signature is something-over-eight, then each eighth note gets a beat.
The most common time signature is 4/4, and it’s often called “common time”. Very straight forward. Pretty much all marches are in 4/4 (they have to be for the left-right-left-right part of the equation). On sheet music, common time is often denoted as a C. “This Little Light of Mine” is in common time (see below).
Next most common is probably 2/2 (that is, two beats per measure, and each beat is a half note), and it’s called “cut time” or “half time”, because you’re basically taking 4/4 and making it twice as fast. On sheet music, cut time is often denoted as a C with a vertical line through it, like a large cent mark.
Three-quarters’ time is 3/4 - three beats with each beat being a quarter note. Very simple to count: one-and-two-and-three-and. This is what waltzes and many other dances are written to.
Five-eighths time is counted like this: “one-two, one-two-three”. My first high school band director taught us to say “I love POST Toasties. I love POST Toasties.” to get the count right.
Seven-eighths time is counted like this: “one-two, one-two, one-two-three.” Both 5/8ths and 7/8ths tend to have fast meters.
There are some other really squirrely time signatures out there, but those are probably the most common. Just remember that, other than marches, the emphasis of the beat always falls on 2 and 4 in common time. Friends don’t let friends clap on one and three.
For example, when you sing “This Little Light of Mine”, you clap on the capitalized syllables, because that’s where beats two and four fall:
This LITtle light OF mine,
I’m GONna let IT shine.
This LITtle light OF mine,
I’m GONna let IT shine.
Hope that helps.
To me, jet engines are perpetual motion machines. They work by shooting out hot gases out of a nozzle, using a mechanism that is powered by those same hot gases. I’m afraid one day everyone is going to realize this and they’ll just start dropping out of the sky like rocks.
But how do you tell where the measures are, if you’re listening to it?
For me, it’s calculus. Even though I’ve forgotten most of my high school trig in the intervening years, I did very well in it and understood it just fine.
Then I got to calculus in my senior year, just barely got a passing grade, and every concept I’d struggled so hard to learn all year went fluttering away the instant the last bell rang. I’ve been able to fit every other kind of math I’ve encountered into a certain nuts-and-bolts view of the world, but calc just never made any logical sense to me.
Always? Isn’t that really just in jazz/rock/pop/country/hip hop? I don’t think that much classical music (as little of it that is in common time) has a back beat.
And aren’t a lot of marches in 2/4?
Having said that, 3/4 is not the same as 6/8. It’s not like reducing fractions.
Maggie, sometimes it’s just intuitive. In a waltz it’s pretty easy. But I often have problems telling if something is in 4/4, 2/4, or 2/2.
I’m with the OP: music and electricity. My brain simply isn’t wired to understand music–I like music, and can appreciate it, but I don’t get it.
When I was around 6 years old, I took piano lessons using (I think) the Suzuki method (I found it on Wiki, so that sounds right). What I learned then and in school was pretty much what phouka is saying, but nope, it just doesn’t get through.
So I put on some John Coltrane or Stevie Ray Vaughan, and simply enjoy it and I don’t analyze it.
The same for electricity. I understand hertz, but can’t grasp the difference between voltage, amperage, and watts. I’d need something like a first grade explanation in order to get it.
FWIW, I consider myself fairly bright–I understand, for a layman anyway, physics and most sciences.
There are math concepts that I still can’t wrap my head around. I started a thread on the two envelope paradox and all I accomplished was annoying people with my inability to see what they said was obvious. Based on that experience, I didn’t even bother starting a thread on Cantor dust.
The differences between lay/lie and affect/effect. Oh, I learn them even some handy tricks, but they’re quickly forgotten and I’m back to thinking of other ways to phrase what I was going to say instead of using them.
Ayuh, and I think I may…possibly…finally get when to use that/which. But I’m not making any promises.
Women?
Speaking Martian?
Stranger in a Strange Land?
Okay, I got nothing.
Windows. I learned Unix first, and I just think in Unix.
I can’t tell you what time signature any piece of music is in, unless someone has told me or I’ve seen the sheet music. Same goes for what key it’s in. I know what time signatures and keys are, but I just can’t hear them in a piece of music at all.
Not quickly in my head.
My trick was always to subtract 2 instead…example:
1300 is 1:00. Subtract two from the second number. 3 - 2 = 1.
1900: 9 - 2 = 7. 1900 is 7:00.
Works a little differently over 2000. For that, I remembered that 2400 would be midnight, so if I saw 2100 I just knew that 9:00 was 3 hours before midnight.
When you use it every day, you do start to think in 24-hour.
Okay, fine, not always. A lot of the time. Probably more than half. YMMV. However, if it’s the kind of song you can sing and clap to, you’re probably going to get funny looks if you’re clapping on one and three. Just saying.
I suppose. In seven years of band (four in marching band), the number of marches we played written in 2/4 time was surpassingly small.
You are correct. Three-four time would be counted “one-and-two-and-three-and” where six-eighths time would be counted “one-two-three, one-two-three”. Three pairs of two compared to two pairs of three.
Errrrrr . . . I don’t have a verbal explanation for it. I can point it out to you on sheet music (look for the thick vertical lines on the staff). Listening to music, I can usually figure it out by “feel”. There are certain patterns you get used to hearing and playing - like, songs rarely begin on beat 1. They almost always begin with a pick-up note - that is beat four or the “and” of four before the first full measure.
If we were listening to the radio together, I’d be able to count out the beats for you and say “here it is”, and probably still not be able to explain why it is so.
In pop and rock music, in general the bass and kick drum play the first beat of the measure, and sometimes the third, while the snare drum and rhythm guitar play on the second and fourth.
Usually.
phouka, my dear, you do realize you are doing just what the OP describes?
“You don’t get X? Here, lemme 'splain it to you…”
<some 'splainin occurs>
"But what about Y? What about Z?
“Oh, here you go” <more 'splainin>
“Better?”
“Yes - thank you.”
But that “better” is just for now. I remember when Dopers **Pasta **and **Stranger on a Train **and a few others contributed to an “Ask the Particle Physicist” thread. It was great! I learned a ton - now ask me if I remember *any *of it 
w/r/t Music and meter, unless the person brings an innate sense of meter, or immerses in it for a while (it sounds like you are a musician from your posts), the learning, it does nothing! Or, more accurately, it mostly fades away, with maybe a trace remaining.
I remember trying to explain Dave Brubeck’s Take Five rhythm to a non-muso - they got it while I explained it and saw how I clapped through the meter, and marveled at how the 5/4 beat “worked” - but when we next got together, he said “yeah, remember Take Five? That was great. Can’t follow it anymore, but I like the song more now.” Heck, I’ll take that.