Stay Together
Sep 1, 2005 12:00 PM, By John McJunkin
In today's music, groove and timing are everything. If you don't get those two elements right, your tracks are simply not going to pop. To get the timing just right, you first need to know the dangers of some common mistakes and misconceptions. By examining several technical pitfalls that cause a lot of heartburn and frustration, you can learn to avoid them so you can stay focused on what's important: the music!
OOPS! WRONG TEMPO
First, and above all else, when working on a prerecorded piece of music (a remix, for example), you must know exactly what your tempo is. I did a little experimental mash-up of a famous 1980s synth-pop piece with an acoustic cover of the same song. After pitch-shifting each song halfway toward the other's key to arrive at the same tuning, I calculated the tempo of the original remix by using Digidesign Beat Detective to initially locate a marker at the first beat of the song (there's an introductory swell at the very beginning). I then used Pro Tools' Tab to Transient feature to get a precise four-bar selection. I clicked on Analyze in Beat Detective and then clicked on Generate, which in turn gave me a tempo of 118.4519 bpm. I established another track and inserted the Click plug-in so that I could actually hear what was going on in terms of the tempo.
As it turns out, Beat Detective calculated my tempo a wee bit fast — this piece could not be any more precisely 118.4 bpm (a fact I happened to be aware of in advance). That extra 0.0519 bpm caused the Click plug-in to get ahead of my audio pretty quickly. It doesn't take much to throw things off. Although I blamed Beat Detective, it's completely my own fault. The problem here is the statistical sample size. When pollsters take polls to determine whether people like one brand of peanut butter more than another, they can't ask everyone in the world, so they take a statistical sample. With peanut butter preferences, it doesn't take a huge sample to get an accurate picture. In my synth-pop case, however, it takes a bit more, and I only took a sample of 16 quarter notes. In this 6.5-minute piece of music, there are 783 beats. Sixteen out of 783 is a small sample (just a bit more than 2 percent). The trick is to select a much longer chunk of the song to get a more accurate tempo.
Using Beat Detective is one way to do it (as is using Pro Tools' Identify Beat command), but a couple of other old-school mechanisms will also work. One is to literally count the beats in the song, divide the number of beats by the number of minutes (represented to the most decimal places possible) and thus arrive at a pretty accurate tempo. One important thing to remember here is that you have to work “modulo 60,” as the mathematicians say. In other words, a 4-minute, 35-second song is not the same as 4.35 minutes. Just take the number of seconds after the final full minute (the 35 seconds in this example) and divide by 60. Thirty-five divided by 60 equals 0.58333, so the correct time is actually 4.58333 minutes. Your calculated average tempo will be more accurate if you get a very precise measurement of the length of the song in minutes. Counting beats can get a little tedious, so count bars and multiply by the number of beats per bar (the numerator in the time signature). Like Beat Detective, this gives an average tempo. Also, don't get fooled by extraneous issues like meter — it doesn't matter whether the song is in 3/4, 4/4, 7/4, 9/8 or whatever. Counting the true number of beats and dividing by minutes accounts automatically for the time signature when calculating tempo because bpm is, by mathematical definition, beats per minute, regardless of how many beats per bar.
Stay Together The other down-and-dirty way to get a precise tempo is to follow the previous directions for Beat Detective to get a ballpark tempo and then listen to the click track late in the song. If the tempo is off, it will be more obvious toward the end of the piece. Make trial-and-error changes in the tempo, and listen again toward the end of the song. If Click is right smack with your song all the way to the end, you can be assured that you've got the tempo exactly right.
Still another key issue here is changing tempo. Luckily, some pretty powerful software is available these days to handle the math for you, but definitely be aware that you want everything in your mix to change tempo the same way — audio and MIDI data alike. Bottom line: Make sure you have every track selected before you change tempo in any way, shape or form. Also, if you have sections of the song with drastically differing tempos, you'll obviously need to work on each section individually to make sure everything lines up.
FIBBING TO YOUR COMPUTER
Getting the tempo exact is important but so is making precise selections. In particular, you have to not only select the correct length of audio but also correctly inform the computer of the length of your selection. For instance, in the Beat Detective window, you are asked to enter the beginning and the end of the selection. Usually, the selection will commence with beat 1 in bar 1. The tricky part is the end of the selection. It would be tempting to put beat 4 in bar 4 (for a four-bar selection), but that couldn't be more wrong. The true end of the selection is the first beat of the next bar, which, in this example, is bar 5. Otherwise, you're getting a 15-beat selection, and when you tell Beat Detective that it's 16 beats, the tempo will be significantly miscalculated. So make sure that you're telling the computer the correct length of the selection you've made — in this example, from bar 1, beat 1 to bar 5, beat 1.
LOOPS OF THE WRONG LENGTH
Another selection bugaboo relates to loop cutting. Ninety-nine times out of 100, you'll need to cut loops to start on the downbeat of the measure and to finish at the first beat of the following bar. Moreover, the selection will probably be an even number of bars, even if you're using an odd time signature. The exception to this rule occurs if you are intentionally attempting to create something that's evolving or abstract. Certainly, some experimentation with loops of odd bar lengths mashed up against loops of even bar lengths can yield some pretty hip results, but if you're trying to color inside the lines, your loops should be of even bar lengths. The more insidious problem with cutting loops occurs when you get one that just isn't quite as long as it's supposed to be. If you cut a loop that's short by, say, a 64th note, you can run into some real trouble.
For example, say you're using Pro Tools, and you are in Shuffle mode. As you begin to stack iterations of your loop one after another, you are losing a 64th note of time with each one. Sixty-four bars into the piece, you are going to be a full bar fast. Similarly, if you cut the loop one 64th note too long, you would then be a full bar slow once you get 64 bars in. Precision is of the essence when cutting loops. A solution is to avoid using Shuffle mode — choose whichever mode in which your DAW will place the beginning of the loop according to relative, not absolute, time (for instance, Grid mode in Pro Tools). In other words, your DAW should “know” where the bar is supposed to start. This enables you to easily place the loop so that it starts right on the one of every bar.
MIDSTREAM TEMPO CHANGES
Obviously, numerous applications are now available that almost completely idiot-proof the process of building song arrangements — Ableton Live, Sony Acid and Image-Line FL Studio are examples. These apps correct tempo automatically; nonetheless, you must be aware that even when tempo is perfect and the loop is cut exactly right, inconsistencies in live human performances can result in things not quite lining up. In the case of drums, percussion, rhythm guitars and other transient rhythmic loops, the application of an extracted (or commercially available) groove can help line things up a bit, but when it comes to vocals and other less transient things, some manual editing to tighten up the timing is likely necessary.
Usually, a vocal is going to be on a linear track instead of being looped; thus, editing it is a bit easier. The earlier example of mashing up an organic, acoustic version of a song with the dancey, drum-machine-precise original really points out the problem of drastic midstream tempo changes. The original dancefloor version is robotically precise and consistent in tempo, but the acoustic version, which is quite literally just a fingerpicked acoustic guitar and a female vocal, has drastic tempo swings throughout, as good live music typically does. The point is, although you can conform audio to a groove, be aware that you can only go so far. Groove quantization of the audio can be useful but only to an extent. You may have to do some drastic manual surgery to get things lined up precisely the way you want them.
KEEP IT STRAIGHT
The reason that I've spent most of this article helping you to get these fundamentals right is, once you do, almost anything you could possibly want to accomplish becomes a lot easier when you've taken care of tempo and selection issues the right way to begin with. Among other neat things, Beat Detective enables you to extract a groove from a piece of audio or a MIDI sequence and apply it to another piece of audio or another MIDI sequence. Propellerhead ReCycle does the same thing with loops. Similarly, Live allows you to apply grooves to loops, as well, not to mention other types of signal processing and time-stretching, such as the various granular-resynthesis-based Warp modes.
Getting all of the timing and tempo issues straightened out at the onset makes the rest of the process much more transparent. What's more, when you're working in a DAW, getting the tempo of all elements perfect from the beginning enables you to just drop things in here and yank them out there, with everything lining up. Attempting to go back and fix tempo issues when you're halfway into a project can be a giant pain — if not downright impossible. So get it right from the get-go, and treat yourself to an enjoyable, creative process.
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