STEREO LISTENING GUIDE

Mid / Side headphone test: centered versus wide sound

Hear the difference between an identical signal in both ears and a signal with opposite polarity. Here is what the Mid and Side buttons actually do.

Mid is the shared part of a stereo signal

In a stereo recording, the left and right channels can contain both shared and different information. Mid is derived from their sum: M = (L + R) / 2. A sound sent equally to both ears with the same polarity is Mid-only. On headphones, it often feels as if it is in the middle of your head.

The Mono control in the middle of Earphone Check’s headphone image extracts (L + R) / 2 from the selected source and sends it equally to both ears. It is useful for noticing whether the sound seems to lean to one side. Fit, ear-tip seal and device balance settings can all influence that impression.

Side is the difference between channels

Side is derived from the channel difference: S = (L − R) / 2. To hear a pure Side signal through two headphone channels, the signal is sent to one side with opposite polarity in the other. Either Side control at the outer edges of the headphones extracts that difference from the selected source and plays it with opposite polarity between ears. This is different from panning a sound entirely to the left or right.

The Side signal may feel broad, diffuse or harder to locate. How it feels varies between listeners and playback setups. It is not a claim about how wide your headphones are, and it is not a better or worse version of the Mid sound.

Compare without changing the volume

1. Wear both earpieces and lower your device volume.
2. Turn off Mono Audio, spatial audio and surround effects for the comparison.
3. Choose stereo music or noise, then tap Mono at the center of the headphone image.
4. Tap either outer Side control to hear the difference between the original channels.
5. Switch between Mono and Side without restarting the sound. Tap the same active control again to pause; tap again to resume.

Both modes use the same recording and volume setting. Their loudness can differ because the mix may contain more shared content than stereo differences. Sine and square tones have identical channels, so they contain no Side signal; Side is correctly silent for those sources.

Why can Side disappear in mono?

A mono downmix combines the left and right channels. Equal signals with opposite polarity cancel when added together. If Mono is audible but Side is quiet or silent, the selected source may have little or no stereo difference. Also check whether Mono Audio is enabled somewhere in the playback chain. Speaker playback also mixes acoustically in the room, so use headphones for this specific check.

Mid / Side is not a frequency test

The word Mid here refers to the middle or shared stereo information. It does not mean midrange frequencies. Bass, middle and high frequencies can all appear in Mid or Side information, depending on a recording’s mix.