Stereo Widener Online

How the Audio Stereo Widener works

Stereo widener online: how it works

Stereo width is how far a mix seems to spread beyond the two speakers. A narrow mix sits in a tight cluster between them; a wide one wraps around the listener. Width is one of the things that separates a finished, professional-sounding track from a flat demo, and it is also one of the easiest things to overdo. This tool changes the width of any stereo file using the same mid/side technique found in mastering plugins and hardware, while keeping the bass under control.

How the stereo widener works

Any stereo signal can be rewritten as two other signals:

• Mid = (L + R) ÷ 2, the average of the channels. It holds everything in the centre: usually the vocal, kick, snare and bass.
• Side = (L − R) ÷ 2, half the difference. It holds everything that makes the left channel differ from the right: panned guitars, stereo reverb, room sound and synth pads.

Left and right are rebuilt as L = mid + side and R = mid − side. Widening turns the side signal up before rebuilding; narrowing turns it down; zero side gives mono. Because the mid signal is never touched, the level and position of centred elements stay exactly where they were. That is the big advantage over tricks such as short delays between channels, which widen but smear the centre and cause phase problems.

How to read the result

• Source shows the channel count, sample rate and length. A mono file shows a warning instead, because it has no side signal to widen.
• Width is the setting as a percentage: 100 leaves the file unchanged, 0 collapses it to mono and 200 doubles the side signal.
• Side gain converts the percentage into decibels: 20 × log10(width ÷ 100). 150 % is +3.5 dB, 200 % is +6.0 dB, 50 % is −6.0 dB and 0 % shows the floor of −60 dB. Mastering engineers usually think of width in these terms, and a change of 1–3 dB is already clearly audible.
• Bass mono below is the crossover frequency. Below it, the side signal is left as it was and is not widened.

Choosing a width

• 100–130 % adds a subtle sense of space to a mix that sounds boxed in. This is the range most mastering engineers stay in.
• 130–160 % is an obvious widening that suits pads, ambient music, backing vocals and stereo keyboards.
• 160–200 % is a strong effect for sound design and electronic music. Past this point the side signal starts to rival the mid, the centre recedes and the mix sounds hollow.
• Below 100 % narrows the image. That rescues a track that was widened too hard, tames a stereo reverb that swamps a voice, and makes music sit behind speech in a podcast or video. Broadcasters often narrow music beds for exactly this reason.

Why the bass stays centred

Low frequencies carry very little directional information to the ear, so side energy in the bass adds nothing you can hear as width. It costs headroom, makes the low end sound loose, and on vinyl can make the stylus jump, which is why cutting engineers require mono bass. Club sound systems often run a single mono subwoofer, so any bass in the side signal is lost or cancels. The tool splits the side signal with a gentle filter: above the frequency you set it is scaled by the width, below it it passes through unchanged. 120 Hz is the default and a common mastering choice; 80–100 Hz keeps more of a deliberately wide bass synth, 150–200 Hz is safer for dense electronic tracks, and 0 widens everything.

Tips and pitfalls

• Check in mono. Everything in the side signal cancels when a track is summed to mono, as it is on a phone speaker, a smart speaker, a shop's ceiling speakers or many Bluetooth speakers. The wider you go, the more a mono listener loses. Run the result through stereo to mono and listen for instruments that vanish.
• Headphones exaggerate. Width sounds much bigger on headphones than on speakers. Judge on speakers, or on both.
• Widen the parts, not the whole. If you have the multitrack, widening a pad or backing vocal usually sounds better than widening the finished mix, because the vocal and kick stay solid.
• Watch for clipping. Boosting the side signal can push one channel past full scale on loud material. The tool clamps peaks, which prevents invalid samples but causes audible distortion on heavy settings. Turn the file down first with the audio volume changer, then widen.
• Mono files cannot be widened. A mono recording, or a stereo file with identical channels, has zero side signal, so scaling it does nothing. Width has to be created with reverb, delay or double-tracking first.
• Fix problems before widening. If the channels are reversed, or one side is out of phase, widening makes things worse. The audio channel swapper and the guide to fixing a stereo recording cover those faults.
• Loudness can fool you. A wider mix can sound more impressive at first simply because there is more energy in the sides. Compare at 100 % and your setting at the same level before committing.

The file is processed in your browser and never uploaded. Keep the original, since narrowing a widened file back down does not perfectly restore any peaks that were clamped.

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