RunTheTests
/

Stereo Balance Test

Check the stereo image sits dead centre, and find how much correction it needs if not.

centre

Slide until the sound is dead centre

leftcentreright

With the slider where it is now, where does the sound seem to come from?

How this test works

An identical signal is sent to both channels, which should be perceived as coming from directly in front of you. You then move a slider until it does, and the amount of correction needed is the measurement: if you had to push the image right, the left channel is arriving louder. The test signal is a 500 Hz triangle rather than a sine, because a pure sine is genuinely difficult to place — localisation relies partly on timing differences between the ears, and a continuous sine offers almost none. Adding harmonics gives the ear something to work with. Before concluding anything about the hardware, the result points at the operating system's balance control, which causes this far more often than any speaker does.

What the results mean

Correction needed
How far you had to move the slider to centre the image. Zero is balanced.
Louder channel
The side the image pulled toward before correction.
Under 5%
Within the range that seating position and room asymmetry alone produce. Not worth chasing.
Over 20%
Large enough to be a real level difference somewhere rather than the room.

Common problems and fixes

The image pulls left no matter what I do
Check the operating system balance slider first — it is the cause in most cases. Then swap the left and right cables at the amplifier: if the pull swaps sides the fault is upstream, if it stays it is the speaker or the room.
It is centred on headphones but not on speakers
Then it is the room and your seating position rather than the audio chain. Sitting even slightly off-axis moves the image noticeably.
It is off on headphones too
That points at the headphones, the output, or asymmetric hearing. Try a second pair of headphones to separate the first two from the third.

Frequently asked questions

Why does my sound pull to one side?

Most often the operating system's balance control, which is trivially nudged and essentially never looked at. After that: seating position, a level difference in the amplifier, or a partly failed driver. Asymmetric hearing does it too and feels exactly the same from the inside.

Why not use a pure tone for this test?

Because sine waves are hard to localise. The ear places sounds partly by comparing arrival times at each ear, and a continuous sine gives almost no timing information. A triangle wave has harmonics that provide it.

Is a small offset a problem?

Under about 5%, no — that is within what seating position and normal room asymmetry produce on their own. It is worth investigating when it is large enough to be obvious on familiar material.

More in Device