Eventide H7600

Recording Equipment

The following article, Wave Phase and Cancellation - Part 2, covers the physical causees, acoustic impact and solutions to the phenomenon of audio wave phase cancellation.

Wave Phase and Cancellation - Part 2

continued from Part 1

So it is with sound – two very similar (or identical) waveshapes, perhaps from two mics covering the same source, or two identical copies of a sound played together in a digital editor (DAW), can collide unhappily when mixed together, resulting in a wide range of possible effects, from a weakening of the bass tones in the sound, to subtle, or extreme, tonal shifts, as the monitoring is switched between stereo and mono, right up to a radical loss of virtually the entire program sound of the affected tracks, even though each individual waveshape is recorded at a high level. If this happens, and what goes missing is your main rhythm guitar track, or something equally important, the results could be disastrous to your mix. Since any problems caused by acoustic phase won’t show up clearly, unless the signals are actually mixed together, the rule is: Always check your stereo mixes in mono, to show up any unknown troubles.

There are, of course, ways to deal with the problems created by phase issues before they happen, such as the X-Y pair mic technique. Another quick rule-of-thumb for using two mics is the 3:1 Rule, useful when the conditions require that the mics are spaced apart (a spaced pair), rather than close together (a coincident pair), as is the case with the X-Y. Here, place the first mic facing the sound source, at a mid-distance (say, 2 feet/60 cm), and then, place the second mic not less than three times this distance from the other one, or in this case, about six feet, or 180 cm, apart from it, at the same distance from the source as the first mic is. By doing this, there will likely be enough difference between the program content reaching each mic, that any phase issues will hopefully be minimized as a result. While this is not necessarily a perfect quick-fix, and mono checking must still be done, and adjustments made, for optimum results, it is a good starting point to work from. With a bit of effort, a professional-quality stereo recording can be achieved, with coherent phase, and a wonderfully wide, spatial aspect to the sound. If, after a few tries, the adjustment part of this is frustrating you, I suggest placing the mics so that they face outwards, away from each other a bit (even as much as 90 degrees), so that the aspects of each side of the source that each mic captures will be truly unique, giving even better phase consistency in mono.

Just to make a point about mono checks, while many folks rationalize that music nowadays is almost always heard in stereo, and that "their" mix will "never" be played in mono, they are fooling themselves. Most AM radio, some FM stations, many hotel, commercial and institutional applications, and most live-sound systems will take whatever is input, and send it out in mono, so if your mix is not mono compatible, you may get an unpleasant and public surprise, more often than you'd like.

Go back to Part 1 of this article

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Eventide H7600

The Eventide H7600 is a stereo, programmable, multipurpose, 24-bit/96kHz digital audio signal processor with UltraShifter ™ capability and is the single-processor companion product to the Eventide's H8000FW. The H7600 can do most everything the multichannel H8000FW can do, but in stereo. The variety of possible effects is virtually without end. And, if that's not enough, it boasts nearly three minutes of sample time in addition to 40 seconds of delay time!

Once again, the Eventide H7600 continues the "modular programming paradigm" that made the DSP4000 famous - programs are composed of individual building blocks, or "modules", that allow the user to create and save completely original custom programs. For the user who needs a mega-processor like the H8000FW, but is working in a stereo environment, the H7600 repesents an affordable solution in an elegant and uncompromising package.

Contact Rock Shop Pro Audio for information and pricing on the Eventide H7600 and Eventide products.

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Wave Phase and Cancellation - Part 2

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