If you like to compose using sample loops, you know what a hassle it can be to match up tempos. Of course, there are programs like Sony's ACID and Cakewalk's SONAR that help with this problem by automatically adjusting the tempo of a loop to match the tempo of your current project. But what you if want to do it the other way around? As in matching the tempo of your project to an existing sample loop?
It's actually quite easy to figure out the tempo of an existing sample loop as long as you know how many musical beats it contains, the sampling rate at which it was recorded, and its length in number of samples. If you don't know the number of beats in the loop, you'll need to listen to it and figure it out by ear. To find the sampling rate and length in samples, however, just load the file into your favorite audio editing application. In Sony's Sound Forge:
1) Choose File > Open to display the Open dialog box.
2) Select your sample loop file (you may need to change the Files of Type parameter depending on the format in which your file is saved).
3) In the bottom portion of the Open dialog box, look at where it says Length. The number in parenthesis is the length of your loop in number of samples.
4) Look at where is says Attributes. The number that shows a frequency in Hertz (Hz) is the sampling frequency of your loop.
Now that you have all the information, you simply multiply the number of beats by the sampling rate. Then multiply that result by 60, and then divide that result by the length of your loop in number of samples. What you end up with is the tempo of your loop in beats per minute (bpm).
For example, if you have a loop that is one measure long in 4/4, it would have 4 beats. And let's say its sample rate is 44,100 Hz (CD-quality), and its length in samples is 107,342. To find the tempo of this loop we would do the following arithmetic: (4 x 44,100 x 60) / 107,342. This would give us a tempo of 98.6 bpm. See how easy it is to work with sample loops? Now go and make some music!
To stay informed about new tips, be sure to click here to sign up for the DigiFreq Music Technology Newsletter. It's free!