Timing Is Everything

Long ago, before there were sound systems, the staging of musical performances was determined by the ability of the performers to hear one another. With the advent of the stage monitor loudspeaker, the musicians were free to move about a much larger area, while demanding that every nuance of the sound they produce (and sometimes even the sound made by others in the band) to be clearly audible. In-ear monitoring has provided an even greater range in which these expectations must be met. Unfortunately, the sound of the instruments travels relatively slowly through the air. As the sound sources are spread out across the stage, the transit time for the acoustical sound from the instrument (most noticeably: the drums) to other microphones can cause slight echoes or flamming. Can digital mixers provide a solution?

Once audio has been digitized, adding signal delay is relatively easy. Digital audio mixers typically provide variable signal delay on each input and output (this is in addition to the fixed delay of approximately 1.25 ms as the signal passes through the A/D and D/A conversion). A few minutes with a measuring tape during stage setup or a scaled stage plot, and you might be able to clean up the sound quality of leakage between instruments. The result may even transform the typical rock n' roll leakage from that smeary mess that destroys the presence of the instruments, to that openness that defines great jazz recordings (OK, not always, but it's worth a shot).

The primary staging difference between a traditional jazz quartet and guitar band is the space between the instruments. While the jazz quartet will perform within arm's reach of one another, the guitar band usually spreads out to fill the size of the stage. This latter case may result in a 20-foot space between a guitar amp (acoustic sound source) and the drum kit. This translates into an 18 ms delay added to the snare drum when picked up by the guitar amp microphone. If you review the stage plot with these acoustical propagation delays in mind, you may find a way to minimize the "roomy" quality that is generated by this leakage.

As with much of life, this is not as easy as it may seem. Create a scale drawing of a stage plot and convert each of the distances between microphones from feet to milliseconds by multiplying the distance in feet by 0.885 (at 72 degrees F). Then start with the largest distance to a significant microphone. For instance, a stage-right vocal mic that picks up a significant amount of snare drum directly from the drum riser is 27 feet away yielding a transit time of 24 ms. Then consider the path length to each of the remaining microphones with excess snare drum leakage, such as the lead vocal (21', 19 ms); stage left vocal (24.5', 22ms); lead guitar mic (20', 18ms); bass guitar mic (7', 6 ms); and rhythm guitar mic (17', 15 ms). Now the entire drum kit must be delayed by 24 ms, and each of the other mics are delayed by lesser amounts (24ms minus difference in path length to yield delay times), such as stage right vocal 0 ms (our longest path), stage left vocal 2 ms, lead guitar 6 ms and bass guitar 18 ms. This will minimize the inherent delay in the leakage from the snare drum into these other mics and produce a much tighter sound. However, it cannot stop there or the timing of the band will fall apart.

The next step requires that the signal from the drum kit be delayed to the downstage monitors (or in-ear monitors) to ensure the timing of the musician remains in sync. While it's unnecessary to delay the drum kit to monitors in the back line; it is absolutely necessary to delay the drum send to the front line. This can tighten up the onstage sound, as the acoustical output from the snare will arrive very close to the snare-sound in each monitor. However, if the front line monitors are too loud, their sound could arrive back at the drum kit over 40 ms later, creating an even bigger problem.

What is really necessary to make this work is a signal matrix that allows each onstage monitor to receive delayed signals from each microphone that are aligned with the timing of the sound received acoustically. The technology is available now, but it is certainly not a part of the typical digital audio mixer. The delays can quickly get out of hand (time). In the same way that feedback is best addressed at the source (move the mic or loudspeaker); leakage between microphones might be better addressed through changes in physical layout and microphone choice. Too much delay and the show might not happen on time.

United Entertainment Media Inc.
460 Park Avenue South, 9th Floor
New York, NY, 10016
Ph. 212-378-0400
FAX 212-378-2160

page construction