Why do people say "an octave louder"?

“Louder” is a perfectly correct synonym for “more loudly”. (And for many adverbs, the -er form is the only correct comparative. For example, you can say “play an octave faster”, but not “play an octave more fast” or “play an octave more fastly”.)

It’s been light-years since I’ve heard anyone use that phrase.

Which would make the expression (metaphor?) ambiguous: It could mean either: (1) you have actually heard somebody use the phrase before, but it was a long time ago or (2) you have never heard somebody use the phrase before.

Or it could be that I was making a dumb but appropriate joke by misusing the term “light years” as if it were a unit of time rather than one of distance.

Right. This would add a couple of inches to the original weight of the expression.

Actually, a “quantum leap” doesn’t refer to any particular distance: It just refers to getting from point A to point B without ever meaningfully being at any point in between. Which is a fair enough layman’s description of what happens in a real quantum leap.

You do realize there is both a canon answer to this as well as a plausible real world answer that bogh make that work right?

Who’s bogh?

Yup; I know the canon answer. What’s the real-world one?

11:8=One Tufnel.

It belongs in the same category as Han Solo making the Kessel run “in 12 parsecs”.

i.e., it’s bullshit.

(emphasis added by me)

13, not 12. Eight notes to get from one note to its next octave, such as from A to next A, using our conventional major (or natural minor) scale; 13 to get from one A to the next using halfsteps the entire way.

A A# B C C# D D# E F F# G G# A

A canon at the octave?

Well, I guess it depends on whether you count the octave note or not. I would call a diatonic scale a 7-tone scale, and a chromatic a twelve tone one. There’s only seven unique tones in an octave in a diatonic scale. Just like you don’t count the octave in a pentatonic. It’s a five note scale, not six.

I would accept either descriptive approach, but I was replying to engineer_comp_geek who described the octave as having 8 notes and comparing that to the semitone scale which was then described as having 12.

It has to be either 7 and 12 or else 8 and 13, for consistency.

This makes no sense. Just sayin’.

If you count to 13 you are going to be counting to 11 for the next octave you go down, unless you want to really confuse yourself and lose the plot. There are 12 unique pitch classes. It’s only confusing to say 13.

An octave though implies that you are repeating the tonic at the end. You know that going in but you aren’t counting keys or frets to do it. Not confusing.

When you’re freaking PLAYING a semitone scale you play 13 notes. Just like when you’re playing a standard major scale you play 8. Yes, a standard major scale has only 7 unique notes (the octave is a duplicate of the note you started on) and, similarly, a semitone scale has only 12 unique notees (the octive is, once again, a duplicate of the note you started on.

When I was a teenager, practicing my electric guitar, my dad once asked me to “turn it down a couple octaves”.

I’m a bass player now.

I’ve heard it as a punchline to a joke told by a military musician about a clueless colonel. Never heard anyone use it for reals.

What part of it doesn’t make sense? To be consistent, he’s right: it’s either 7 & 12 or 8 & 13 for both scales from octave to octave. However, for whatever reason, people tend to double count the octave in a diatonic scale for 8 notes (I guess to have “octave” make sense, although a major or minor scale is heptatonic, not octatonic), but not in the chromatic scale.