New phase and polarity tools for MOTU mk3 interface owners

CueMix FX has been updated yet again with two new visual diagnostic tools for stereo audio signals: an X-Y Plot and a Phase Analysis. These real time displays join three other recently introduced tools (the FFT, Spectrogram and Oscilloscope) for a total of five powerful new features now available as a free download for all owners of mk3 FireWire audio interface products. Phase and polarity are critical elements of any stereo mix or multi-mic recording session. Find out how you can improve your sound with these advanced, yet easy-to-use tools.

X-Y Plot
The X-Y Plot window graphs a stereo signal on a standard grid with left-channel amplitude on the x-axis and right-channel amplitude on the y-axis. Stereo material that is said to be “in polarity” (i.e., phase aligned) appears along the x = y axis.

Stereo material that has phase problems will appear along the x = -y axis meaning the signal will appear predominantly in the upper left and lower right of the display. A signal with an extremely wide stereo field will appear much more randomly (not along either axis).

Phase Analysis
The Phase Analysis window graphs frequency versus phase difference versus amplitude of a stereo signal on either rectangular or polar coordinates. In the rectangular view, the vertical axis represents frequency, and the horizontal axis represents the phase of the left channel minus the phase of the right channel. Stereo audio that is predominantly in polarity will appear centered along the center vertical axis.

Frequencies that would be canceled by summing to mono are those that touch the -1.0 or +1.0 lines on the left and right.

In the polar view, the radius represents frequency and the angle (theta) from the +y vertical axis represents the phase difference of left channel minus the right channel. Stereo audio that is generally in phase will appear along the +y axis (above the center point). The more the audio signal “tips” to the left or right, the more out of polarity it is. If it is completely out of phase, it will point downwards from the center point and hover around the -y axis (the part of the y axis below the center point).

Phase analysis can be used for a broad range of applications in the studio and on the stage. Here are just a few ideas:

  • Recording with multiple mics — the Phase Analysis window lets you compare multiple mic sources with each other to check for potential phase cancellation caused by varying distances in mic placement from the recorded source.

  • Checking the overall polarity of a stereo mix — quickly check for phase issues in your stereo mix.

  • Summing to mono — if your stereo material needs to be summed to mono, Phase Analysis lets you see what frequencies will be canceled out when summed.

  • Tuning and checking PAs or sound reinforcement — place mics in strategic locations in your venue to check for critical phase issues in the listening environment.

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