Stereo Test — Pan & Phase Check
Stereo test checking left-right identity, an 8-second pan sweep and mono compatibility with polarity flip. Find routing faults fast. Free in your browser.
Protect your hearing. Start at a low volume. Never raise the volume to make a tone audible. Levels are shown in dBFS, relative to full scale — not SPL.
How it works
A 440 Hz sine is routed through sub-millisecond DelayNodes for timing, per-ear gains for level, and a StereoPanner for position. The pan sweep follows an equal-power curve over an 8 second loop. A polarity toggle inverts the right path and a mono sum adds the channels, so inverted content cancels to near silence, measured in dBFS. Nothing is uploaded or recorded, and no sound plays until you ask for it.
A stereo perception test confirms your system images correctly: left is left, right is right, motion between them is smooth, and the mix survives a mono sum. Confirm channel identity with a 440 Hz tone, follow the 8 second pan sweep from ear to ear, then flip polarity and switch the mono sum on to hear out-of-phase content collapse. Everything runs live in your browser — nothing is uploaded — and no sound plays until you ask for it.
Left and right identity
Choose Left, Both, or Right and play the reference tone. Both should sit dead center; Left and Right should be hard-panned with silence on the opposite side. Swapped labels mean a reversed cable, adapter, or OS balance setting.
Pan sweep
The sweep loops left, center, right, center on an equal-power curve, so loudness stays even while position moves. Listen for smooth travel with no clicks, gaps, or one-sided dips.
Mono compatibility and phase
Set a manual pan, invert polarity, and toggle the mono sum. In-phase sums reinforce and read higher on the meter; inverted sums cancel and the verdict reports near silence.
Aliases covered on this page: stereo test, stereo perception test, left right stereo test, pan sweep test, and mono compatibility test.
Frequently asked questions
What does the stereo perception test check?
Three things — that Left really comes from the left and Right from the right, that a slow pan sweep glides smoothly without jumps or dropouts, and that your system sums to mono correctly with and without a polarity flip.
How do I confirm left and right identity?
Play Left, then Right, on the identity panel. A 440 Hz tone plays hard-panned to one side. If the labels sound swapped, a cable or an operating-system channel setting is reversed.
What should the pan sweep sound like?
An 8 second loop moves from left through center to right and back. The image should glide continuously. Sticking at the center, sudden jumps, or a level dip on one side point to a balance or routing issue.
What is the mono and phase check?
The mono sum adds left and right together, the way a single speaker hears them. With both channels in phase the sum reinforces, and with one channel inverted the two copies cancel to near silence. The level meter and verdict show the collapse.
Why does out-of-phase content cancel in mono?
When two identical signals are added with one inverted, every positive sample meets a negative one of the same size, so they sum to zero. In-phase copies double instead.
Is this safe for my hearing?
Start at a low volume. Every section starts only from a button you press, a persistent Stop and Mute are always available, and levels are reported in dBFS, relative to full scale, never in SPL.
What is stereo imaging?
Stereo imaging is how convincingly your system places sounds between and beyond the speakers, from hard-left through center to hard-right. Stable imaging needs matched channel levels, correct polarity and symmetric placement. If the pan sweep sticks, jumps or collapses in mono, suspect balance settings, swapped wires or room asymmetry.