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A quick way to confirm your left and right channels are wired correctly. Play a tone on either side individually, on both at once, or pan it back and forth across the stereo field. Useful for headphones, speakers, car audio, and surround setups.
Pick a routing pattern. The tone is the same 440 Hz sine — only the channel changes.
A stereo channel test plays a known signal on a specific channel so you can hear which speaker — or which side of your headphones — is producing the sound. It catches the everyday problems that ruin a listening experience: a left/right cable swap, a dead driver, an XLR with reversed polarity, or a balance knob that's been bumped off-centre. Run it before you commit to a long listening session, set up new monitors, or troubleshoot a noisy stereo. This tool plays a 440 Hz sine tone (concert A) through the Web Audio API, with four routing modes: left only, right only, both channels in mono, and a slow continuous pan from left to right and back.
Sit in the listening position you actually use — between the speakers, or with your headphones on the right way around (most have an L and R inside the cup).
Press play. The sound should come exclusively from your left side. If you hear it on the right, your channels are reversed somewhere in the chain.
Switch to right-only mode. Confirm the tone has moved fully to the right. Both ears should agree on which side is producing the sound.
In mono mode, the tone should appear to come from straight ahead (or, on headphones, from inside your head).
Switch to sweep mode and let the tone pan back and forth. The motion should sound smooth and continuous — no jumps, no dead zone in the middle, and no level imbalance favouring one side.
A pan position is a number between -1 (full left) and +1 (full right). The two channels are derived from the input level and the pan: panLeft = (1 - p) / 2 when p ≥ 0 panRight = (1 + p) / 2 when p ≤ 0 More commonly, an equal-power law is used so the perceived loudness stays constant as the tone pans across: L = cos((p + 1) · π / 4) R = sin((p + 1) · π / 4) The Web Audio StereoPannerNode used here applies a smoothed linear pan, which is fine for diagnostic tones.
When you pan a mono source, you are not literally moving the sound — you are adjusting how loud it appears in each channel. Your brain interprets the level and timing differences between your ears as direction. This works perfectly on headphones (where each driver feeds one ear) but only approximately on speakers, because both ears hear both speakers; the cabinet placement and room acoustics matter too. A correct stereo test lets you hear which ear is being addressed by which channel, independent of the room.
Reference: MDN — StereoPannerNode (Web Audio API)
| Mode | Expected result |
|---|---|
Left only | Sound entirely from the left side; right side silent. If reversed, your speaker cables or headphone wiring is swapped. |
Right only | Sound entirely from the right side; left side silent. Confirms the matching channel from the previous test. |
Both (mono) | A phantom centre image — the tone appears to sit between the speakers. If it pulls left or right, your speakers are mismatched, the room is asymmetric, or one channel is louder. |
Sweep | Smooth motion from one side to the other and back, with constant loudness. If it briefly disappears in the middle, you may have a polarity (phase) issue. |
Find your high-frequency hearing cutoff with a 20 Hz - 22 kHz sine sweep.
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Live input meter with peak, RMS, and clip detection — no recording.
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