View Full Version : Messing with a WAVs BPM.

Dash Myoku
11-20-2009, 01:02 AM
Ok...so, lets say I have a WAV that's of a song. Something that plays on the radio, but it's just vocals. No background music or anything. Now, what I want to do is compose music around that, but I find that I have BPM problems later on. Measures don't line up right and by the end, it's a big mess of crap.

So, is there any way to have the WAV play at a certain BPM so I can arrange music around it without it getting off track?

Patrick Burns
11-20-2009, 02:54 AM
Lots of programs have BPM detectors so you can set the tempo of your project to that of the wav. (necessary example so I'm not useless: Logic has a BMP detector plugin out of the box, but I'm sure you can find free ones) I'm not sure of something that automatically does the reverse.

Some tracks just aren't perfectly consistent throughout, though. All I know to do is just be as exact as possible with your project's tempo, and adjust it at different points throughout the project to keep things lined up.

11-20-2009, 03:00 AM
bpm = (beats * 60) / seconds

So if you count the number of beats in a segment of the song, multiply that by 60, then divide by the exact length in seconds of the segment, you'll get the exact tempo of the song in bpm.

(If you're still set on stretching it, you can rearrange the equation to figure out how long you should stretch the sample to produce a specific bpm.)

EDIT: This equation assumes the tempo stays the same. As Patrick points out, if the tempo fluctuates (like if it wasn't recorded to a click track) then you just have to follow it as best you can

11-20-2009, 03:02 AM
In the program I use, Reaper, I right click the WAV I'm editing, click on Item Properties, and there's an area with a 1.00000000 in it called playback rate. Since 1.000000 is the original playback rate, you would pretend that means 100% of the original BPM. From here on, our imaginary BPM is 160. If you replaced 1.000 with .5, it'd play at half speed, or 50%, which is about 80 BPM. if you made it 1.25, it'd play at 1.25 times the speed, or 125%, which would be around 200 BPM.

In whatever DAW you're using, there should be a similar function.

Dash Myoku
11-20-2009, 03:37 AM
Mm, maybe I oughtta find a BPM detector some where. And yeah, constantly having to change the tempo to match the WAV's seems annoying...but doable, to say the least. Thanks Patrick.

Thanks for the equation, Moseph. I hadn't actually thought of the mathematical relevence with BPM, but it seems like it'd be helpful if I wanted to figure out the BPM of songs when I'm not at home.

I'm using FL7 and I don't think I've really come across anything that similar to doing that, like Reaper. Maybe...something to definitely look in to. Thanks Luke.

11-20-2009, 07:04 PM
Ableton Live doesn't do anything else than stretch/compress wave files to their correct lengths.

Thing is, when that happens you lose some of the quality and punch of the original, though there are several "smart" algorithms that can find out (or have to be helped a bit) that you're stretching a drum loop so they use a different method that simply detects the separate drum sounds and expands or contracts the space between 'm.

11-20-2009, 08:52 PM
I use a free DJ program called Rapid Evolution (http://www.mixshare.com/) to get the BPM and it seems to do a good job. Plus it does a host of other things as well.

11-21-2009, 05:07 AM
if you're dealing with acapella vocals, the only way is to manually find the BPM. I usually do this by making a basic metronome beat (a hi-hat or something every quarter or eight note) and placing the vocals on top of it. Then I just adjust the tempo until they are in sync. Sometimes the vocals aren't at a consistent BPM, so in that case I cut the lyrics into sections and make sure each section is in tempo