BMP of imported audio to match BPM of MIDI in garageband

Question

Level 1

8 points

BMP of imported audio to match BPM of MIDI in garageband

Hi guys,

I've imported an mp3 into garageband. I'm trying to create my own beat (using the garageband drum kits) to be played over a the imported mp3, however I don't know the best way to go about matching up the BPM.

I don't know the BPM of the mp3. It seems as the the BPM is somewhere between 113 and 114 (to my best estimate). How do I either:

a) Stretch the audio so it fits a certain BPM

or

b) Find out exactly how many BPM the mp3 is so that I can record my MIDI at the same BPM?

and after that, what's the best way to time shift the mp3 so that it's beat aligns with the MIDI metronome?

Any help would be GREATLY APPRECIATED. Thanks!

iMac G5 2.1 Ghz Mac OS X (10.4)

iMac G5 2.1 Ghz, Mac OS X (10.4)

Posted on Jun 12, 2007 10:04 PM

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Answer 1

Jun 12, 2007 11:50 PM in response to castlljs

That is a hard job in GB, and maybe even impossible ... but let's see …

First question: Does your mp3 have a consistent beat at all? If it's a modern studio production, probably. If it's a live recording of a band, maybe not. How did you "estimate" the bpm? I use two principal methods:

The first one is record on a new track in GB so I hear the metronome, stop, adjust the tempo, record, adjust, etc., until they are in perfect sync. If you're lucky, the song was recorded with an integer bpm number, and you're done.

Second: Count the beats on a longer stretch of music, preferably an integer number of bars, and measure the time. You can do that rather precisely in GB. Then do the math to determine the beats per minute (I leave the formula to the reader as an exercise).

If the bpm number is non-integer (and I don't mean 119.95, which is probably some calculation effect), you can't fix it in GB. You should go to an audio editor (e.g. Audacity) and time-stretch your mp3 slightly so it hits the nearest integer bpm value (again, do the math to find out the percentage of speed-up or slow-down you need.) Import the new sound file into GB and set the tempo to the value you just created.

Use the audio editor window and magnify to align the sound file to the bar grid. If you've done everything right, you can now add drum loops to the song. Still, don't expect perfect results!

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Answer 2

castlljs Author

Level 1

8 points

Jun 13, 2007 12:19 AM in response to Christoph Drösser

Thank you for the quick reply.

I just used a program on my windows based computer that has a "tapping" function to measure the BPM. If my ears and fingers were coordinated enough, the BPM of the imported audio file is 111.7 BPM (not an integer).

I actually JUST downloaded Audacity as a result of searching through these forums. I'm learning how to use right now.

If I need help learning how to stretch the audio, I'll post again, unless you know off hand of some trick or easy way to do this in Audacity. Thank you very much!

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Answer 3

Jun 13, 2007 1:37 AM in response to castlljs

Hm, I'm a bit suspicious if this tapping yields the correct number ... 😉

But if it is correct: You should speed up your song in Audacity by .27 percent, or factor it by 1.0027 (don't remember how Audacity measures that) to get to 112 bpm. That's hardly audible but should give you a good result (if your tapping is correct by .27 percent ... 🙂

Maybe before going through all of this, you should try out if you can match beats to your song at 112 bpm.

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