Splits a stereo mix into mid (center) and side (left/right difference) content and rescales the sides — collapse a mix toward mono, or widen it for a bigger sound.
The Stereo Width Adjuster makes a stereo mix narrower or wider. Widen a thin mix, narrow an over-wide one, or collapse it toward mono. It only changes the side signal, so centred vocals and kick stay put.
A bass mono option keeps everything below a chosen frequency in the centre — the standard practice for mixes destined for vinyl, clubs and phones.
Left and right are converted to Mid = (L+R)/2 and Side = (L−R)/2. Width multiplies the Side signal: 0 gives mono, 1 the original, 2 doubles the side level. For bass mono the signal is split with a subtractive crossover — a Linkwitz–Riley low-pass (two cascaded 2nd-order Butterworth filters, 24 dB/octave) at your frequency, and a high band equal to the input minus the low band, which recombines perfectly. The low band is summed to mono, the high band widened, and the two added back together.
Widen pads and guitars.
Narrow an over-wide recording.
Keep the low end mono.
Check a mix collapses well.
| Width | 0–200% |
|---|---|
| Bass mono | Off, or 5–300 Hz crossover |
| Method | Mid/Side with subtractive crossover |
Mid is what both channels share (centre); Side is the difference between them (width).
Slightly; the limiter keeps peaks safe.
It uses mid/side processing: mid = (L+R)/2 is what's shared by both channels, side = (L−R)/2 is what differs. Scaling the side signal changes perceived width without touching the centered content.
Pushing width very high can hurt mono compatibility — parts of the mix may partially cancel when played on a mono speaker or phone. Check the result in mono if that matters to you.
This tool runs entirely in your browser using the Web Audio API. Nothing is uploaded, stored or shared — there is no server to send your file to, so it works offline once the page has loaded.
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