| Beyond Quantization The human dimension of computerized rhythms by Jim Aikin The quest for better-sounding MIDI tracks is never-ending. And since rhythm is arguably the most basic aspect of music, it makes sense that sequencers give us some powerful tools with which to control the rhythmic side of our music. The best way to get your sequencer to play flexible-sounding, expressive rhythms is to perform them yourself (or have a keyboard-playing friend do it) and then fix any little errors one note at a time, by hand. Don’t have the patience? Then try applying the tools described below. One or two preliminary points before we start: Normally, quantization changes the start time of notes, but not their length (also called duration). Some sequencers let you correct the length at the same time you’re correcting the start time, so that all notes both start and end on the rhythmic grid. To my ear, this type of edit sounds very stiff and artificial, and I never use it. If you’re playing a monophonic synth patch such as a lead or bass tone in legato mode, quantizing can change the accents and articulations of the line. This is because some notes that were overlapping slightly in your original, unquantized performance may not overlap after the rhythm is corrected -- or vice-versa. (Look at the first two notes in Figure 1a vs. Figure 1b for an example of this.) Legato mode is a synthesizer option that causes a new envelope attack to be generated only after a period, however brief, in which no note was being played. Hand-editing of the note lengths may be necessary after quantization to get the envelope attacks/accents onto the correct notes. *** 0107_feature_04_a.jpeg goes here *** Caption: I could fill pages with nifty diagrams explaining quantization. This one will have to do. We're looking at the piano-roll display in a sequencer whose clock resolution is 480 ppq, and the vertical lines represent sixteenth-notes and beats. The part played in (a) has not yet been quantized. In (b), we've applied ordinary sixteenth-note quantization. Notice that the lengths of the notes have not changed, only their start times. All the start times are now on the sixteenth-note grid. Some notes (such as the first one) have been moved only slightly, while others have been moved quite a bit. In (c), notes that fall within a "window" of 15 clock ticks before or after the sixteenth-note grid have not been moved, while those further away have been quantized to the grid. As it happens, neither type of sixteenth-note quantization works very well with this passage, because it contains a fast lick just before beat 2. Looks rather like a 32nd-note triplet, doesn't it? A better approach would be to select the first three notes and quantize them, but leave those leading into beat 2 unquantized. Quantization Types * Swing - When you quantize using a standard (non-swing) setting, the rhythm is "corrected" in such a way that all of the notes are aligned with an evenly spaced grid (see Figure 1b). If you choose sixteenth-note quantization, each note will start precisely on some sixteenth-note within the bar. With sixteenth-note swing, however, the grid is skewed in such a way that the second, fourth, sixth, and subsequent even-numbered sixteenth-notes are delayed. This causes the notes on the eighth-note grid (the next higher resolution than sixteenth-notes) to sound slightly longer and the notes that fall in the spaces between eighth-notes to be slightly shorter. The note lengths haven't actually changed, but because their start times are different, the rhythm acquires a long-short, long-short feel. But how long is long, and how short is short? That's controlled by the swing amount parameter. Most often, this parameter is shown as a percentage of the next higher rhythmic resolution. For instance, a 50% swing amount is no swing at all, because each sixteenth-note is 50% of the length of an eighth-note, as usual. A 66% swing gives you a triplet feel, and 75% swing corresponds to a dotted-eighth/sixteenth rhythm. When programming funky rhythm grooves, I sometimes give different swing amounts to different instruments -- 54% to the cowbell and 58% to the kick and snare, for example. To my ears, this makes it sound as if the components of the groove are being played by different percussionists. * Strength - Another useful quantization parameter is called strength or amount. If you quantize with 50% strength, each note will be moved halfway from its original position to the nearest grid position instead of being rigidly quantized to your chosen rhythmic grid. This is useful for tightening up a rhythm that was played a little too loosely, without making it sound totally rigid. * Window - Sometimes you want to leave the subtle rhythmic nuances of a performance entirely untouched, and only quantize the notes that are grossly out of alignment. The tool for this job is the quantization window setting (see Figure 1c). Usually, this is set up so that you can specify a number of clock pulses (see last month's column for more on clock pulses) on either side of the beat. Notes that are closer to the beat than this value -- say, within ten clocks before or after a given beat -- are not quantized, while those that are further away are corrected. * Humanize - Some sequencers let you "humanize" a quantized rhythm by randomly adding a few clock pulses to or subtracting them from the start time of each note. The idea is that this produces a less robotic feel. The trouble is, the variations in time introduced by human performers aren't actually random. Good players play with slightly elastic rhythms, but they tend to push the beat at certain spots and lay back at other spots for expressive musical reasons (even if they're doing it unconsciously). "Humanized" quantization is a very poor substitute. Much better is... * Groove - With groove quantizing, you don't align notes to a uniform grid. Instead, you align them to a more complex grid that you've defined yourself. Check your sequencer's manual for specifics, as this feature is implemented in various ways. You may be able to set up a groove template in which beat 2 of each 4/4 bar is a bit late, for instance, while beat 4 pushes ahead. Groove quantization may also give you control over the relative velocities of notes on individual beats. I've heard some Latin groove templates that were extremely realistic -- when applied to the right percussion track, of course. Some audio sequencers will even let you "quantize" your MIDI data to the rhythm of an audio file.
|
