Metric modulations and tempo changes

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Metric modulations and tempo changes Anonymous 2022-09-13 (Tue) 19:44:22 No.6330

Okay guys, I have a question for any musicians or people who are good at maths (ideally both).

I was trying to figure out a metric modulation in the song Ancient Temperament by Eidola. The first section (approx 2:58 in the video) is in 6/8, and it then goes into a section in 4/4 . However, if you keep tapping the 8th notes from the previous time signature you end up with a 3/2 polyrhythm, which means that there is not only a time sig change but a tempo change. What's more, if you clap that 3/2 polyrhythm through the 4/4 section, you will find that it changes back to 6/8 at the previous tempo (around 3:28), and you're then clapping 8th notes as you were before.

I managed to figure out that if the first section in 6/8 is at 90bpm, then next in 4/4 must be 126bpm. The problem is… I have no idea how I managed to figure that out. I've double checked my maths, and I did the sums wrong, but somehow still ended up blundering into the correct answer.

I can also even tell you that you could play half note triplets in 4/4 at 225bpm and get the same pulse, but again, I have no idea how I managed to figure that out. I've been puzzling over this since just after I figured it out the first time around, and I can't even understand how I came to the conclusions I came to.

How would you go about figuring out this tempo change, /music/?

Anonymous 2022-09-13 (Tue) 19:51:43 No.6331

compound times like 6/8 are actually 2/4 divided by triplets.
By your description you could write down the whole song as 12/8 and have some passages where all the notes are dotted and have passages where a lines plays a rhythm with all the notes dotted against another where all the notes are triplets.

Anonymous 2022-09-13 (Tue) 20:47:43 No.6337

>>6331
True, but it's more of a feel thing. For instance, the verse is divided up between bars of 5/8, 6/8 and 3/4. The tempo is the same between the bars of 6/8 and 3/4 so there is no polyrhythmic sillyness, but the drum pattern changes so that the snare hits on the "and" (1 and 2 and 3 and), so whilst you can count it as 6/8, it's not a very accurate description.

Besides which, I don't think this solution solves for the added tempo change in the section I described.

Anonymous 2022-09-15 (Thu) 11:22:20 No.6342

File: 1663240940580.png (26.25 KB, 812x527, Ancient Temperament metric….png)

For what it's worth, I have an easier way of explaining this now.

As you can see in pic rel, the strumming pattern of the section in 6/8, if divided up correctly, matches the tempo of the next section in 4/4. All you have to do is bring the pule forwards an 8th note so that instead of dividing into 2x3s, it divides into 4 sets of an 8th note plus a 16th note (4*1.5).

From there, it should be much easier to figure out the acual bpm tempo change in future.

As an aside, that rhythmic pattern is the same as one used by Roger Taylor from Queen in a lot of their songs. For example, you could quite easily put the rock section of Bohemian Rhapsody in 6/8 if you wanted to and it would still work.

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