Basslane is the original freeware classic used in countless productions to narrow the stereo width of low frequencies in tracks and mixes. This is useful when mixing to regain bass tightness and prevent “muddy” mixes caused by a too wide low end. Basslane is also very useful when mastering and especially when mastering for vinyl records. It allows you to transparently prevent problematic stereo content in the low frequencies.
Get it from toneprojects.com: Basslane