Channel Isolation Test
Find out whether one side is dead, the sides are crossed, or everything is coming out of both.
Volume warning
This test plays tones that can be loud and may damage hearing or speakers. Turn your volume down before starting, then raise it gradually.
How this test works
Three tones play in a known order — left only, right only, then both — and you say where each one came from. The tones are routed through a channel merger rather than a balance control, so the channel that is meant to be silent receives nothing at all rather than a small amount, and they are faded in and out over twenty milliseconds because the click of an abrupt start is broadband enough to be audible through the silent side and would fake the bleed the test is looking for. The three answers are then read in a fixed order of precedence: a dead channel is identified before a swap is considered. That ordering matters more than it sounds. If your left output is silent, then hearing the left test tone on the right is simply the right speaker doing its job — reading it as a swap would turn a broken speaker into a wiring diagnosis and send you looking at cables that are fine.
What the results mean
- Isolated
- Each tone arrived on the side it was sent to and the both-channel tone arrived on both. Your output keeps the channels separate, which is what stereo material needs.
- Swapped
- Both channels work but they are the wrong way round. Nothing is faulty and nothing needs replacing — it is headphones worn backwards, reversed speaker cables, or an adapter wired the other way.
- Bleeding
- A tone sent to one channel was audible on both sides. On headphones that points at the equipment; on speakers it is usually the room, since sound reaching your other ear off a wall is physics rather than a fault.
- Silent on one side
- One channel produced nothing while the other worked. Check the balance control before anything else — a slider pushed fully to one side is indistinguishable from a dead speaker in this test and is far more common.
Common problems and fixes
- One side is dead but the headphones work on your phone
- Then the headphones are fine and the computer is not. Check the balance setting in sound preferences, then try a different socket. On a laptop, a partially seated 3.5mm plug produces a dead channel that comes and goes as the cable moves.
- Everything arrives in the centre on headphones
- Look for a mono audio setting. Both Windows and macOS have one under accessibility, several phones enable it for hearing accommodations, and it is easy to switch on by accident and never notice on speech.
- The test says bleeding but only on speakers
- That is normal in most rooms. Speakers placed close together, or a desk and walls reflecting sound, will always deliver some of each channel to both ears. Re-run it on headphones for a result about the equipment rather than the room.
- The tones are too quiet to place confidently
- Raise the volume moderately and run it again. Anything you have to strain to locate will produce inconsistent answers, and the test would rather report an inconsistent result than guess.
Frequently asked questions
Why does it check for a dead channel before a swap?
Because a dead channel makes swap detection meaningless. With no sound from the left, the left test tone can only be heard from the right — which looks exactly like crossed wiring but is not. Checking in that order means a broken speaker is reported as a broken speaker.
Why not use a balance control to send the tone to one side?
Because a hard pan still leaves a small amount of signal in the opposite channel on some implementations, and a small amount in the channel that is meant to be silent is exactly what this test is trying to detect. A channel merger writes true silence into the other side.
Is this the same as the left-right swap detector?
They overlap deliberately. This one asks three questions in a known order and covers dead channels and bleed as well as swaps. The swap detector asks six in a random order, which removes the expectation that comes from knowing which side is next — the better tool if a swap is what you actually suspect.
Can the page tell whether my speaker is broken?
No. It can tell you that no sound arrived on one channel, which is the same observation you would make yourself, structured so it is not confused with a swap. A balance slider, a cable, a socket, an amplifier and a speaker all produce an identical result here, and separating them means swapping one part at a time.