FEELIN' GROOVY
By Craig Anderton
Groove Examples 1-3 Liquid Audio Groove Example #1 WAV
240K MP3
176K Note how the orchestral kick drum comes in just a little bit later than the downbeat, thus adding suspense. (Excerpt from "Paradise," from the Forward Motion CD by Craig Anderton and Spencer Brewer, Sona Gaia CD-157, distributed by MCA.) Groove Example #2 WAV
256K MP3
192K In this excerpt, the snare drum hits a few milliseconds after the beat, thus "dragging" the tune's tempo. (Excerpt from "Time Trap," from the Forward Motion CD by Craig Anderton and Spencer Brewer, Sona Gaia CD-157, distributed by MCA.) Groove Example #3 WAV
256K MP3
192K In this file, there are two places where the bass slides. The first slide, which lasts two beats, has been "stretched" about 15 milliseconds by slowing the tempo.
The second slide lasts four beats. The first two beats are stretched about ten milliseconds, the second two beats about 45ms. These slightly lengthened slides add tension as the piece modulates up. (Excerpt from "Technophone," Craig Anderton, unreleased.)
In the quest for perfection in MIDI and digital audio recording, there's the nagging feeling that something has been lost: the "feel" that makes music groove like a human musician instead of a machine. But as usual, technology is a two-edged sword. While it can steal the feel if misapplied, when used creatively it can help enhance a groove.
This month we'll cover some of the factors that contribute to feel, as well as digital audio edits that help put the groove back into music. Because this subject is also important to MIDI sequencing, next month we'll look at the subject of feel, groove templates, and timing from a MIDI standpoint.
The "Feel Factor"
Much of the interest in feel traces back to a landmark article written by Michael Stewart in the mid-'80s that documented the importance of timing in determining a piece's "groove." Two important concepts were how playing slightly behind the beat creates a bigger, more laid-back feel, and how pushing the beat leads to a more intense, "nervous" feel.
There are many implications. One is that the best human drummers control timing accurately to within milliseconds, as verified in later experiments. Also, the lead/lag relationship between instruments is crucial. For example, even when the kick and hi-hat stay rock-steady, moving the snare forward or backward can make a huge difference in feel. And if the kick and the bass guitar or bass synth hit at the same time, delaying the bass slightly behind the kick makes it less prominent and emphasizes the rhythm, while sliding it in front of the kick accentuates the bass, highlighting the bass line's harmonic content over the rhythm.
Another implication is that techniques such as quantization and snapping to a grid, which produce perfect timing, can actually be anti-musical. Yes, there are forms of music that in theory benefit from a "machine vibe," but even with the most metronomic techno, introducing some timing changes can add interest and build tension/release better than keeping the groove perfectly aligned.
Adding Feel with Digital Audio
Although some people seem to forget this, the easiest way to record a human feel is to hire a good musician. If that's not an option, there are many ways you can mess around with timing.
First, when recording drums, allocate a separate track to each drum sound if possible. (If you don't have the track count, consider a mix of MIDI and digital audio, such as using digital audio for cymbals and other sounds that don't sound realistic if the same sample is being triggered over and over, and MIDI for kick and toms.) In a digital audio editor, this allows you to slide individual drum parts back and forth in time simply by grabbing a track and moving it. Even slight changes can make a big difference -- 5 milliseconds (ms) is a significant shift in feel-land, and it's unlikely that you'll exceed ±10ms.
Sliding a track is a fairly global maneuver; many times, you'll just want to move one or two strategic hits. For example, in the tune "Paradise" from my last CD, there's a section with a fairly steady orchestral drum pattern. Then voices come in and sustain while the drum drops out. When the drum re-enters four beats later, the downbeat hits just a tiny bit late. As a result, the brain expects the beat to fall in a particular place, but is fooled by having it hit a little later than expected. This adds interest, and also builds up the tension a bit just prior to the drum's re-entry. (You can hear this example, as well as some others showing the effects of "feel" edits, at the top of this page.)
Many programs (Digidesign Pro Tools, IQS Samplitude, Emagic Logic Audio, Steinberg Cubase Audio, etc.) allow user-placeable/editable snap points. Editable snap points make it easy to change the feel by placing the point a little later or earlier than the beat. The advantage of snapping to a point rather than just sliding audio around is that it simplifies replacing the sound later on, as well as providing a template if you want several parts to hit at precisely the same time.
Tempo Time
One difficulty with digital audio arises when you need to change the tempo after something has been recorded, the way you can easily do with a MIDI sequencer. You have two options: variable speed, which lengthens or shortens the musical material to change tempo but also changes pitch, and time compression/ expansion ("time stretch") algorithms, which change length but don't change pitch. Unfortunately, these algorithms also affect sound quality, and tend to give more objectionable results when processing stereo program material.
The best solution is to vary both pitch and duration before recording your melodic parts, as "varispeed" algorithms are kinder than time-stretch algorithms to drums and percussion. Algorithms that change duration without changing pitch are another matter. Of course, the less you stretch, the better. For the slight tempo tweaks that are usually sufficient to add feel -- say, upping the tempo during a solo by 1 bpm, and dropping it down 1 bpm during the chorus -- most algorithms will be satisfactory.
As the amount of stretching increases, quality decreases. Some algorithms (such as the ones in Sound Forge) give you several options so you can trade off timing accuracy, minimum "warble," best timbral preservation, etc. Others are more "take it or leave it," and may be optimized for percussion or melodic signals, but not both.
Because I capture parts to digital tape, it's easy for me to bounce the drum tracks over to a hard disk recorder (via the analog I/O) while varying the tape speed, then bounce back to tape via digital I/O as final storage for the audio. With hard disk recording by itself, you typically define a section of audio and apply some DSP (onboard or third-party plug-ins) to change pitch or do time stretches.
Fig. 1. ReCycle "slices" a loop into individual segments that can be triggered by MIDI notes. The inverted triangles mark the segment boundaries.
The Digital Audio/MIDI Connection
One very clever Mac/Windows program, Steinberg's ReCycle, is optimized for doing feel tricks by bridging the worlds of digital audio and MIDI. For example, suppose you want to slide some beats around in time with a digital audio drum part. ReCycle analyzes the audio file and inserts markers at rapidly rising transients (Figure 1), which usually occur as a result of drum hits or other rhythmically intense events. The program converts each piece of audio between markers into a sample, and assigns these chromatically to a sampler's keyboard map. But the coolest part is that the program also generates a Standard MIDI File (see the menu item in Figure 1). This consists of notes whose timing corresponds to the timing of the markers placed in the loop, and whose pitch matches the appropriate samples now stored in the sampler.
If you play the MIDI file into the sampler, it sounds just like the original loop. But once you start editing in MIDI, the creative options begin. Want the offbeats to hit just a little bit late? Move the MIDI note-ons as needed (logical or conditional editing techniques can help with this, as they can specify edits such as "move all notes falling within ten clock pulses of the second beat four clocks ahead in time"). Instant feel changes!
And speaking of MIDI, groovology is a fact of life in the MIDI world -- most MIDI + digital audio sequencers allow groove templates to be loaded and applied to various MIDI notes. Next month we'll delve into how to integrate MIDI-oriented feel changes with your digital audio.