Phase—What’s the big deal ?

Your Home Studio - a basic tutorial on home recording studio setup, including building a home recording studio, digital recording techniques, computer recording information, recording software information, how to buy equipment for a home recording studio and operating an audio recording studio at home

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      Whenever you are dealing with waves of any sort, you are dealing with phase. It is useful in music production as an effect but it can also present problems in recording. Let’s look at the example of waves on the surface of a pond to understand phase issues, both good and bad.

      On a perfectly still pond, we drop two identical stones in the water. As the waves promulgate from where the stones were dropped they eventually interfere with each other. In the cases where the top of a ripple (wave) meets the bottom of a ripple, the ripples cancel each other out. This is analogous to two identical tracks being 180 degrees out of phase. The places where the top of a ripple meets the top of the other ripple results in the ripple being doubled. In audio terms, the two identical tracks would be perfectly in phase with each other. There are, of course, an infinite number of variations in between 0 degrees (completely in phase) and 180 degrees (completely out of phase) and being 100 degrees out of phase has the same effect as being 260 degrees out of phase. This can be visualized by picturing a circle with 0 degrees at the top and 180 degrees at the bottom. As you can see, every spot on the circle, other than 0 and 180 degrees has a corresponding spot that is the same distance from 0 degrees.

      Phase naturally occurs in the case of two guitarists playing exactly the same piece of music (usually strumming). Because they are human, there will be times when they play it exactly like the other person and times when they are a little behind or ahead of the other person. The places where they play it exactly the same will sound louder and more distinct since they are in phase with each other while the times they are not in sync, the result will be thinner. This is desirable because it forces the listener to pay closer attention. Chorus as effect accomplishes this by splitting the original signal in two and time shifting one slightly. An oscillator controls the amount of the shift randomly, so it sounds natural. Flanging does the basically the same thing by slowing down and then speeding up the duplicate track, again using an oscillator to control the speed. Phasing as effect actually varies the phase by sweeping the amount of time shifting by a predetermined amount. You can also accomplish this effect manually by making a copy of the source track and shifting it slightly ahead or behind (3—7ms) the original. This is what’s known as doubling a track and back in the original days of recording, it would be done by playing or singing the track at least two times and sometimes many times.

      A negative issue with phase is when mic’ing a drum kit or any stereo source. When using two overhead microphones, you must make sure they are far enough apart to cancel out any phasing. Not doing this will result in a thin sounding stereo track that will be difficult to hear in a mix. Some microphone manufacturers are making microphone with 2 capsules situated so that there is no way for the mic’s to be out of phase with each other. One way to detect if two tracks have a phase issue is to listen to them in mono. You’ll hear a difference in the overall volume between the mono and stereo tracks if phasing rears it’s ugly head. If phasing does occur, many software packages and DAW’s include phase switches so you can flip the phase of one of the tracks. This usually takes care of the problem but in the case of a track that is 90 degrees out of phase, you’ll end up with a track that is 270 degrees out of phase ( still 90 degrees from the original).