# 150 to around 120, which bpm is best for pitch?May 23, 2013 8:23 AM   Subscribe

I have a song at 150 bpm, perfectly in tune. I want to repitch it down to around 120 by slowing it down. At which bpms will the notes be at pitch?
posted by semaphore to Grab Bag (6 answers total) 4 users marked this as a favorite

Best answer: Exactly 120 bpm would transpose it a major third down in just intonation, 119bpm for the same interval in equal temperament. Out of curiosity, why not timestretch it?
posted by mkb at 8:27 AM on May 23, 2013 [1 favorite]

Best answer: In general, speeding up by 6% will take the pitch up by one piano-keyboard half step, and slowing down by 6% will take it down one half step. (Technically, it's not 6%, it's the twelfth root of two — but 6% is pretty close.)

If you want to keep the piece in the same key, there's no way to do it within the parameters you've got. You'll need to timestretch instead, like mkb suggests.

If you don't mind changing keys, your options are 141bpm (transposing down a half step), 134bpm (down a whole step), 126bpm (down a minor third) or 119bpm (down a major third).
posted by Now there are two. There are two _______. at 9:12 AM on May 23, 2013 [2 favorites]

What other sounds / music / instruments do you want it to be in tune with? The difference in pitch between slowing to 120 bpm and 119 bpm may be so small as to be indistinguishable, depending on the overall sound.
posted by RobinFiveWords at 11:26 AM on May 23, 2013

I think your terms are confusing. Sorry if you already know this stuff. But if you can answer these maybe I can help:

>>I want to repitch it down to around 120 by slowing it down

120 is not a measure of pitch, it's a measure of beats per minute. You could slow it down to 120 BPM, but the pitches in the tune would be lowered by 120/150 = .8. Each pitch would be 80% as high as they used to be.

>>At which bpms will the notes be at pitch?

At pitch to what?
posted by toastchee at 12:21 PM on May 23, 2013

>>I want to repitch it down to around 120 by slowing it down

120 is not a measure of pitch, it's a measure of beats per minute. You could slow it down to 120 BPM, but the pitches in the tune would be lowered by 120/150 = .8. Each pitch would be 80% as high as they used to be.

They want to slow the music down to around 120 BPM and accept whatever changes in pitch happen. Just like slowing down a tape or record.

>>At which bpms will the notes be at pitch?

At pitch to what?

They want to slow it down by half or full steps, so that whatever notes the song ends up playing are still in tune. If they drop an in-tune C down to an A, they want that A to also be in tune.

As for the actual answer, I'm not entirely sure how to do that math. It may depend on the application you are using. Since notes are geometric (the HZ doubles with every octave), slowing it down to half speed will bring it down a whole octave. And doubling the speed will bring it up an octave. But as Now there are two says, each interval is an irrational number and you can never get it exactly right.

The other thing to consider is that the timbre of the sounds won't be the same. Most instruments play each note with a slightly different tone coloration, and just digitally repitching it by a couple steps can make it sound "off".
posted by gjc at 3:09 PM on May 23, 2013

Do you need to change the pitch as well? Because I know Audacity (and other apps, I imagine) can change tempo and pitch independently. Just checking, wasn't sure from the wording of the question.
posted by sapere aude at 3:17 PM on May 23, 2013

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