Third, if you find low-frequency instruments sound weak even when you boost their low frequencies, there may be phase problems. Second, if a sound seems to come from outside your speakers or from behind you, there may be phase problems. This may be caused by phase differences between the left and right channels. First, pay attention to any stereo sounds that don’t have a focused center image. It is important to listen for comb filtering cause by phase issues. Pink noise suffering from comb filtering How to listen for comb filtering If these signals are added together, the result would be silence. The two microphones’ signals are 180˚out of phase with each other. The first microphone picks up the waveform at its highest amplitude and the second microphone picks it up at its lowest amplitude. Let’s take the example of a sine wave playing from a single speaker and being picked up by two microphones placed at slightly different distances from the speaker. Moving the position of one microphone relative to the other will result in an audibly different blend when the two signals are mixed together. When one sound source is captured by two microphones the resulting output consists of two signals, and the phase relationship between the two microphone signals is significant. A single sound will not be perceived by a listener as having a correct polarity. Phase is a relative measurement, meaning the phase of audio signals really only matters to us when two of the same, or very similar waveforms combine either acoustically or during a mix. When the signal reaches the highest amplitude on the circle and the sine wave, its rotation has covered 90˚. The 360 degrees of phase angle shown on the circle match the phase of the sine wave at the same point in time. Kelley for the National Institute of Standards and TechnologyĪs the green dot at the head of the signal moves, its position can be described in degrees. The animation below shows how a circle and a sine wave can simultaneously represent the phase of a signal by displaying the same signal’s amplitude and angular frequency over time. “ Phase” refers to the position of a sound wave in time, measured in degrees. This will help us mix without worrying about phase issues should our mix fold down to mono. Let’s take a look at what causes phase issues and learn how to avoid recording sounds that can cause phase problems. Mix elements should sound similarly balanced when played back in stereo or mono, and skilled mixers are alert for the problems that folding a stereo mix to mono may create. Mixing to ensure mono-compatibility cannot be achieved with a blanket approach. Essentially, any speaker setup where the speakers are either too close together or too far apart for the listener to perceive stereo sound should be considered a mono playback system. Sound systems in malls, grocery stores, and other public spaces may be mono. Sound systems in clubs and pubs are often mono, as are many subwoofer systems in venues. Is it relevant to listen to or check your mixes in mono in today’s world? Of course, it is. Have you ever listened to one of your good-sounding stereo mixes in mono and noticed that some elements become thinner, weaker, or maybe they’re entirely gone? If so, your mix most likely has some phase cancellation issues.
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