Phase designates a point in a sound wave’s cycle and is also related to frequency, see Fig. 1.3. It is measured in degrees and is used to measure the time relationship between two or more sine waves.
As you can see from Figure 1.6 and Figure 1.7, when two sound waves are in phase, the result is increased amplitude.
When they are 180 degrees out of phase, they can completely cancel each other resulting in little or no sound.
This concept is used in many modern devices, such as noise-cancelling headphones or expensive car mufflers, to eliminate the outside sound or engine noise.
However, sound is not always completely in or out of phase. Sounds can be out of phase by any number of degrees, ranging from 1 to 359. Phase issues can make some frequencies louder and others quieter.
Often a room’s acoustics create these areas of cuts and boosts in the frequency spectrum. These cancellations and amplitude increases influence the way a room is going to sound.
Standing waves and comb filtering are often the result of these phase interferences. Phase is also very important to keep in mind when stereo miking and when using multiple mics on an intended source.
When listening in a typical stereo environment, a sound may be completely out of phase and go unnoticed unless the phase is checked.
Some tips to check phase: Mono button
Phase flip (polarity) Phase meterPhase issues can be exposed when a mix or a sound is checked in mono.
One of the first records I mixed was a new wave record with thick delays and effects. I was mixing a particular track for a music video.
The studio where I was working at that time had a small TV with a mono speaker.
I would patch mixes into the TV in order to hear the mixes in mono. This would expose any existing phase issues and instrument imbalances.
I patched into that TV after completing what the band and I thought was a pretty good mix, and the vocals and keyboards almost completely disappeared!
Imagine if I hadn’t checked the phase in mono.
The video would have been aired and there would have been no vocals.
I can honestly say after that experience that the mono button became one of my go to buttons on the recording console.
Many live music venues and dance clubs’ PAs and speaker systems are set-up in a mono configuration to get more power.
What would happen if one of your out-of-phase mixes were played in a club? It would be less than impressive.
Always check your mixes in mono!