How to Correct or Fix Out of Phase Cancellation in Recordings?

Ever wonder that your recordings during tracking sessions sound very weak when mixed together? The recording might be experiencing an out of phase or phase cancellation problems in audio recording.

Understanding Out of Phase Issues

For those beginners, who simply find this very hard to understand, please take a look at the animated gif below for two mono waveforms (in gray) traveling in the same direction (this is analogous to your two mono signals traveling across the audio cables from microphone to audio interface and then finally to your digital audio workstation software). When they are in your digital audio workstation, these mono signals are summed up during your audio mixing process, the result of the addition of these two waveforms is the color blue below.

Animation Credits: Kettering University

Look very closely, you can observe that:

1.) If two traveling waves or audio signals are “in-phase” or in “timing” with each other. The resulting amplitude (the blue wave) of these two mono signals is maximum (strongest).

2.) If two traveling waves starts to experience some “delay” with each other (they are not synchronized or timing anymore) the resulting amplitude starts to decrease. In actual audio mixing, the sum wave is not as strong as the original inputs. You might wonder why the resulting mix sounds very weak. There might be phase related issues.

3.) If two traveling waves are exactly 180 degrees out of phase with each other, the summation of these waves is actually zero and the result is a complete silence (as you can there is a section where the summation is simply a horizontal line).

In practical audio mixing, phase issues can occur less than 180 degrees so you will still actually hear the results but it will sound weak and unnatural. If you have the symptoms outlined above, you should re-record your material and correct the phase issues. One of the most common causes in phase issues is delays in your recording. These are caused by microphone interference.

Delays caused by Microphone Interference

Phase issues are the results of microphone interference. For example there are two singers (“A” and “B”) performing together at the same time at the same level. When two microphones are used and are placed very near to each other, Singer “A” microphone can pickup the sound from Singer “B” thus causing it to be recorded with a delay. There is a delay because Singer “B” voice arrives at microphone “A” and “B” at different times. See screenshot:

Microphone “A” pickups Singer “B” voices but its delayed with the original waveform as you can see the leaked sound of the waveform does not anymore “in-phase” with the original recording because of the presence of a delay. If this is summed up using an audio mixer, the result is a weak Singer “B” sounds because of phase cancellation. The same thing would happen with Singer “A” on Microphone “B”. Microphone interference is a big problem and if optimal quality in recording is desired, this should be minimized.

3 is to 1 Rule in Microphone Placement Solution

The classic solution to microphone interference causing phasing issues is the “3 is to 1 rule”. This is the statement of the rule:

The distance between two Microphones “A” and “B” should be 3 times the distance of Microphone “A” from the sound source “A” or Microphone “B” from sound source “B”.

So the above problem can be resolved using this concept such as shown below:

If the distance from singer to microphone is 1 feet, the distance between microphones should be around 3 feet to minimize the effect of microphone interference. Although the above example is shown with applications pertaining to tracking vocals; the principle extends when recording any instruments together with more than one microphone. A good example is tracking drums, guitars and other instruments.

Using Directional Microphones to further reduce interference

It makes sense to properly use directional microphones to further reduce phase issues. A good example of directional microphones is cardioid type. Sounds are pickup strongest directly at the front of the microphone with fewer signals on the side. Thus if you aim them at 45 degree to both sound sources, the interference is substantially reduced. See screenshot below:

Because of the microphone directional characteristics, you reduce interference on both sides if you tilt the microphone at some angle pointing directly to the sound source. By observing these practices when recording, you reduce phase related issues in your tracking session.

Content last updated on August 14, 2012