Stereo Channel Test
If a tone lands on the wrong side (or LEFT sounds higher-pitched than RIGHT), your channels are swapped; everything is generated locally in your browser.
How it works
仕組みCheck that your left and right audio channels are wired the way they should be. The tool plays a short tone panned hard left, hard right, or both at once, and gives each side its own pitch (a low 440 Hz note on the left, a higher 660 Hz note on the right), so even a mono downmix or a single working earbud can reveal a swap. Channel reversal is a classic gotcha with renamed Bluetooth earbuds, DIY speaker wiring, and some USB interfaces, and only playing a test tone on your own device can catch it.
For wired speakers, the left/right plugs or speaker wires are simply swapped; trace the cable and reconnect. For headphones, check you’re wearing them the right way round (the L/R marks are easy to miss). Some earbuds and operating systems also offer a balance or channel-swap setting that may have been toggled.
If your system collapses audio to mono (an accessibility setting on phones, or a single Bluetooth earbud), panning alone can’t reveal a swap. The pitch acts as a second fingerprint: LEFT should always be the lower note (440 Hz) and RIGHT the higher one (660 Hz). Hearing the high note on the left means the channels are crossed even if the direction feels ambiguous.
First check whether your OS has a “mono audio” accessibility option enabled; it mixes both channels together on purpose. A very rare cause is a browser without StereoPannerNode support, which the tool detects and tells you about. Room speakers placed close together can also make hard-panned tones feel centred; headphones give the clearest answer.