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Don't put anything in the mix that doesn't need to be heard.

Amen!

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There is a plug-in that can center those frequencies below a threshold, usually 80–120Hz, while panning the frequencies above. I own it and would post a link but am having trouble remembering the name.

A quick search turns up five. I own the BOZ and iZotope plugs. iZotope Ozone Imager 2 is free and the Boz Digital Labs Pan Knob is $49 if not included in a bundle.

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Many plugins can center bass frequencies while allowing you to pan higher frequencies, including specialized stereo imagers and multiband processors. This technique is valuable for anchoring a mix, ensuring the low end has power and mono-compatibility, while giving high-frequency elements space in the stereo field.
Stereo imager plugins with crossover

DJ Swivel Spread: This three-band stereo width plugin allows you to set the crossover points and adjust the stereo spread for the lows, mids, and highs independently. The "sub rolloff" feature can automatically ensure frequencies below a set point are mono.

Boz Digital Labs Pan Knob: Originally designed for panning, this plugin includes a crossover point that keeps frequencies below a certain threshold in the center, while letting you pan the frequencies above it. It is particularly effective for improving headphone mixes and maintaining mono compatibility.

iZotope Ozone Imager 2: A popular, free plugin that offers a straightforward way to widen or narrow your sounds. It includes a "low bypass" feature that keeps the low frequencies in mono while allowing you to expand the stereo image of the rest of the signal.

Waves Center: This plugin allows you to control the center and side levels of a stereo track. It includes a special "Low" control that preserves the levels of low-frequency sounds mixed to the center, making it easy to create a powerful stereo image while keeping the bass mono.

Waves Vitamin: A multi-band enhancer with five frequency bands and variable crossover frequencies. You can control the stereo width of each band independently, making it easy to collapse the low end to mono and expand the highs.

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