# Sub-Bass Mono Maker Fold everything below your crossover to mono while keeping the stereo image above it — the elliptical-EQ move that protects vinyl cuts and mono-sub club systems. > Canonical page: https://elysiatools.com/en/tools/audio-sub-bass-mono-maker - **Category:** Media - **Keywords:** sub bass mono, elliptical eq, bass mono maker, vinyl mastering, mono low end, mid side, stereo bass, club master ## Overview Implements the mastering technique known as elliptical EQ exactly the way vinyl cutting engineers do: the stereo SIDE (difference) signal is high-passed at your crossover while the MID (sum) stays full-range, then L = MID + SIDE and R = MID − SIDE are reconstructed. Below the cutoff the side channel carries almost nothing, so L and R collapse to identical mono with no level change; above it, the original stereo image passes through untouched. The slope (12/24/48 dB per octave) controls how hard the transition happens. Before rendering, the tool decodes the track and measures mid and side energy below the cutoff plus the L/R cross-correlation, so you can see how much out-of-phase low end you actually had; after rendering it re-measures the output and reports the achieved side-band suppression and the new near-perfect below-cutoff correlation. Mastering guidance: keep the crossover conservative (80–150 Hz for most programme material; monoing everything below 300 Hz throws away real width). ## Inputs - **Audio file (stereo)** (file) - **Mono cutoff (Hz)** (number) - **Side filter slope** (select) - **Output format** (select) ## When to use - Preparing club masters to ensure solid low-end playback on mono subwoofer sound systems. - Mastering tracks for vinyl lathe cutting to eliminate vertical stylus excursions caused by out-of-phase bass. - Fixing stereo phase cancellation issues in wide synth patches or multi-mic drum bass recordings. ## How it works - The stereo input is decoded into MID (sum) and SIDE (difference) components while measuring sub-band stereo correlation. - A high-pass filter with a 12, 24, or 48 dB/octave slope is applied exclusively to the SIDE channel at the specified cutoff frequency. - Left and right channels are reconstructed using sum-and-difference math (L = MID + SIDE, R = MID − SIDE) and exported in your selected audio format. ## Use cases - Electronic music producers tightening kick drums and 808 basslines for club sound system playback. - Mastering engineers prepping vinyl premaster files to comply with mechanical cutting head constraints. - Mixing engineers eliminating wide chorus or stereo widening phase anomalies in sub-bass layers. ## Frequently asked questions ### What is an elliptical EQ? An elliptical EQ high-passes the stereo side (difference) channel below a set cutoff so that low frequencies collapse into identical mono while higher frequencies retain full stereo width. ### What crossover cutoff frequency should I choose? Setting the crossover between 80 Hz and 150 Hz works best for most programme material; setting it above 200 Hz can unnecessarily narrow lower-mid instruments. ### Which filter slope should I select? Use 24 dB/oct for general mastering, 12 dB/oct for gentle vinyl mastering transitions, or 48 dB/oct for sharp club-ready sub-bass isolation. ### Does monoing the sub-bass change overall track volume? No. The MID (sum) signal remains full-range and unaltered, meaning center-panned low-end energy maintains its original balance. ### What output audio formats are supported? 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