Stereo Imaging Test
Hear how your speakers or headphones place sound across the stereo field. Sweep a tone from hard‑left through the centre to hard‑right, check the phantom centre, take a five‑position “where is the sound?” quiz, and compare an in‑phase vs out‑of‑phase width demo — all generated in your browser.
ℹ This is a playback-chain and setup check, not a measurement. It confirms your left/right channels are correct, not swapped, in‑phase and roughly balanced. Where a sound appears to come from depends on symmetrical speaker placement, your seating position, the room, and — on headphones — your own ears (HRTF), so a perfectly centred phantom image is about your setup, not a spec of the gear. There is no microphone and nothing is recorded; the tool only produces sound. Use a calibrated room measurement (REW + a measurement mic) for objective imaging/response data.
⚠ Start quiet. Begin at a low volume and raise it gradually — pure tones and noise can sound louder than music and can damage hearing or drivers at high levels.
A · Pan sweep (Left → Centre → Right)
The signal travels smoothly from the left channel, through the centre, to the right channel and back. The marker above tracks its position. The image should move evenly across the front, passing cleanly through a solid centre.
B · Phantom centre check
An identical mono signal plays equally in both channels. With symmetrical, in‑phase, level‑matched playback it should image dead centre — straight ahead between the speakers, or in the middle of your head on headphones. If it pulls to one side, that side is louder or the other is weak.
C · Where is the sound? (5-position quiz)
A short cue plays at one of five positions. Without looking at the marker, pick where you heard it, then reveal the answer. A good setup makes all five easy to tell apart.
Where did you hear it?
D · In-phase vs out-of-phase (width demo)
In‑phase is normal mono: solid, centred. Out‑of‑phase inverts one channel’s polarity — it sounds wide, hollow and hard to locate, and largely cancels if your gear sums to mono. If out‑of‑phase sounds fuller than in‑phase, one of your channels may be wired with reversed polarity.
Ready. Pick a signal, set a comfortable volume, then start a test.
How It Works
Stereo “imaging” is the illusion that sounds occupy specific places between your two speakers (or, on headphones, across the space inside and around your head). It is created almost entirely by the differences between what reaches your left and right ears: small level differences and, for real sources, tiny timing differences. This tool builds those differences electronically. Each test uses the Web Audio API to generate a signal in the browser and route it through a StereoPannerNode, which sets how much of the sound goes to the left versus the right output channel. The result is your browser’s normal stereo output — the two channels your speakers or headphones already use.
The pan sweep ramps the panner from fully left (−1) through centre (0) to fully right (+1) and back, so you can hear whether the image moves smoothly and stays solid through the middle. The phantom centre sends an identical signal to both channels at equal level; when playback is symmetrical and in‑phase, your ears fuse the two into a single image that appears to come from straight ahead even though no speaker sits there. The quiz picks one of five fixed pan positions so you can test, by ear alone, how well you (and your setup) resolve placement. The phase demo uses a channel splitter and a gain of −1 on one side to invert its polarity, recreating the classic hollow, diffuse, “everywhere and nowhere” sound of an out‑of‑phase pair — the same effect a single miswired speaker cable produces.
Two honest limits. First, browser audio output is a stereo (two-channel) bus; you can place sound anywhere along the left–right line with panning, but you cannot reliably address discrete 5.1 or 7.1 surround channels from a web page. Second, what you actually hear depends on your room and ears as much as the signal: speakers must be placed symmetrically with your seat at the apex of an equal‑sided triangle; reflections and an off‑centre seat drag the image sideways; and on headphones the absence of room cues plus your individual head‑related transfer function (HRTF) change where things seem to sit. So a clean result here confirms your playback chain and setup are behaving — it is not a calibrated measurement of the equipment. For objective imaging and frequency‑response data, measure with a calibration microphone and software such as REW.