970's MXR Phase 90

Two microphones positioned apart from each
other will capture sound at different times. When
brought together they will be out of phase. The
Phazer helps solve the problem.

Comb filtering is an effect that is caused when multiple 'out of phase' sound sources are combined. Not only is the fundamental affected, so are the harmonics.

Phazer™ Development

Messing with 'time travel' is not new… In the dark ages... circa 1975, MXR's ground breaking 'Phase 90' effect pedal ignited interest in phasing by way of modulating the phase effect for electric guitar. This inspired the Radial engineering team to start experimenting with analogue phase circuits, not as a modulating effect, but as a phase correction tool that could help solve acoustical problems in the studio and on a live stage.

Phasing.... It's all about time

Few realize that beyond the sweeping phase effect that we hear on guitars, minute phase adjustments can actually lead to creating natural sounds. It has to do with physics or more precisely, the physical location of the desired sound source and the position of the various devices used to capture it.

Let's begin with a simple kick drum and two microphones. When the batter strikes the head, the 'slap' reaches the microphone inside the drum first. Then, a few milliseconds later, the 'boom' developed by the drum shell hits the external mic. So what you have are in fact two sounds that are slightly offset. By introducing the Phazer into the initial 'slap' transient's signal path, we can slide the initial attack so that it coincides with the 'boom. The kick drum goes from being mushy and out of phase to producing a distinct thud.

Now let's consider combining a direct feed from a DI box with a microphone. Sound travels at roughly 340 meters per second (1130 ft/sec) while electricity is estimated to travel at 200,000 meters per second (650,000 ft/sec) or roughly 600 times faster. This means that when you combine the direct feed from a guitar amplifier with a microphone, by the time the amplifier pushes the speaker outwards and the sound travels through air before it enters the mic, it will be minutely delayed with respect to the direct (hard wired) signal. Add the Phazer to the direct feed and you will instantly produce huge, fat guitar tones.

This phase 'mismatch' is even more pronounced when two microphones are used on the same instrument. Imagine an acoustic guitar with one microphone positioned directly adjacent to the sound hole and a second mic elevated and 3 meters (10ft) away to capture the natural room ambiance. Again, the sound arriving at the close mic will arrive earlier while the distant mic will be out of phase. Sound engineers often spend hours moving microphones around the room in an effort to find the sweet spot or the position where phase anomalies will be less pronounced. Align the two mics using the Phazer and all of a sudden, your acoustic guitar begins to sound real.

In phase? No Jim... illogical

These phase anomalies create an effect known as comb filtering. This occurs when the original sound is combined with a delayed version of itself in a given acoustic space. When the fundamentals and harmonics mix together some frequencies will either combine when in phase to amplify each other or they will cancel each other out when out of phase. This of course depends on where you place the two microphones relative to each other and the wavelength. Visually, the resulting frequency response curve looks somewhat like a comb, hence the name comb-filter.
This usually produces a hollow or unnatural tone.

Comb filtering is an integral part of all sounds. Our ears and brain use phase along with frequency and loudness to localize sound. In fact it is impossible to be in perfect phase as each of the infinite number of frequencies has a different wavelength. In other words, if you perfectly time-align 500Hz then 510 Hz will be out of phase because the wavelength is slightly longer.

Since you cannot ever be in perfect phase, don't stress over it.
Use your ears and listen. This is exactly what those finicky engineers do when trying to get a great sound. They listen to the combined sound of the two mics using their ears and move the mics around until it sounds good. It is no different when combining two sounds electronically. This is in fact what the Phazer is all about. It is a device that lets you adjust the phase relationship between two sources by delaying one source. Phase adjusting is most often applied to the nearest source so that the fundamental frequencies line up and sound best.

It is important to emphasize that the Phazer is a tool designed to spur on the creative process. In this day and age of virtually unlimited tracks, using the Phazer in creative ways can produce some fun and unexpected results. For instance introducing out of phase effects can lead to some great sounds. Boston's Tom Schultz created some great 'distant - thin' guitar tones by purposely setting the guitar tones out of phase. Have fun and experiment. Who knows what results you can achieve!

Phazers on Stun!

The Phazer is also equipped with a filter. Here's the logic... If the ear is most sensitive to low frequency phase shift, what happens if we leave the high frequencies alone? In other words, if we filter out the high frequencies so only the low frequencies cancel or amplify, what will occur? The filter basically allows you to focus the effect. The Phazer's filter circuit came from this frame of thought. We then decided to break up the range in two so that the adjustment would be easier. It basically acts like a fine tune control on the Phazer.