- Synchronizing Sequencing Software to a Live Drummer
Introduction and Motivation
One challenge currently faced by rock and pop bands is how to incorporate electronic and pre-recorded musical parts when playing live. In the studio, bands typically use multi-track tape and Digital Audio Workstation (DAW) software to overdub extra parts and combine these together in an offline editing process. In the digital sequencer, audio effects, panning, and volume changes can all be automated when crafting the mix of a song, with the result that listeners are increasingly used to hearing an idealized and transformed representation of sound. These processes contribute to making such performances difficult to recreate live. As a result, bands often make use of pre-recorded audio, either through triggering samples or by playing along to backing tracks.
The problem with this is that the pre-recorded material does not respond to timing fluctuations of the band in the way that musicians do, so that often the musicians are forced to follow the timing dictated by the backing track via a click track. In the studio, there has been an increasing prevalence for the use of click tracks on recordings (Lamere 2009). Often bands record digitally onto DAW software, also referred to as sequencers, which control the playback of audio tracks and MIDI messages. Commercial sequencers include Ableton Live, Pro Tools, Logic Studio, Nuendo, and others. These programs provide an optional click track when recording, thereby providing audible feedback to the drummer and other musicians when recording to ensure that they stay "in time." This means the resulting performance has very accurate timing. When a fixed tempo is used, it simplifies the offline editing procedure, because when sections of audio are moved between different locations of the song they are still at the correct tempo. It also allows timing "quantization," whereby the timing of events is corrected to align more closely with the underlying grid.
Although in the studio these restrictions may also have some advantages, in live performance the backing track restricts the freedom of musicians to make changes in timing and isolates the drummer through the required wearing of headphones. In the situation where musicians want technology to be incorporated into their live shows, there is a need for an accurate synchronization system that keeps the sequencer in time with the band rather than forcing the musicians to play to a click track. In this article, we present an algorithm to control the tempo of sequencer, thereby allowing recorded parts or backing tracks to respond to subtle changes in tempo in the way that musicians would naturally respond when playing together.
We first present relevant background material to explain our design methodology. In the subsequent section, we explain our design of the algorithm and then describe two approaches to evaluating the [End Page 46] system. In order to successfully track the timing variations of a drummer, we first need to look at the nature of drum signals and how drummers behave.
Drumming, Rhythm, and Beat Tracking
In popular music, performers generally take their cue from the drummer and it therefore makes sense to align the sequencer as accurately as possible to the drum beat.
Rhythmic Features of Drumming
In rock and pop music, an interlocking pattern is created by the kick drum (also called the bass drum), the snare drum, and the cymbal pattern, played on the hi-hat or ride. Jeff Pressing (2002) characterizes the qualities associated with what he terms "Black Atlantic Rhythm," the rhythms shared culturally between America and Africa, which have given rise to most forms of popular music: blues, jazz, rock, reggae, hip-hop, etc. The devices used by these rhythms all rely on the "support of a firmly structured temporal matrix," defined as a "groove," characterized by the perception of a regular pulse with a subdivision structure and of a longer repeating time cycle. Rhythmic devices enumerated by Pressing that "build on the groove" include syncopation, displacement, off-beat phrasing, polyrhythm, hocketing (an interlocking pattern shared between multiple instruments), and swing. There is a conflict between a fixed pulse and various timing accents played against it (Waadeland 2001), and individual drum events can...