Speed of sound in air = 343 m/s at 20 degrees C (about 1 ms per 343 mm)
+6 dB SPL = double the sound pressure; +10 dB ≈ twice as loud; -3 dB = half power; inverse-square law drops 6 dB per doubling of distance
How it works
Each ear receives the target voice at a slightly different time (ITD) and level (ILD).
Brain compares the two ear signals and computes the angle the voice is coming from.
It locks a perceptual 'spotlight' onto that direction and voice pitch.
Competing voices in other directions get pushed into the background (masked).
Familiar voice, known pitch, and clear consonants make the lock stronger.
Lose the spatial cues (mono, heavy reverb, hearing loss) and the spotlight slips.
Real examples
Following one friend at a loud party while 20 others chatter around you.
Hearing your own name from across a noisy room snaps your attention instantly.
A parent waking to their baby's cry but sleeping through traffic.
Picking out the lead vocal in a dense band mix because it sits centre and clear.
Catching a gate announcement over the din of a packed airport terminal.
How it helps in live sound
Carve a 2-4 kHz presence boost (2-4 dB) on vocals so consonants cut through crowd noise.
High-pass vocals at 80-120 Hz to clear low-end mud that masks intelligibility.
Aim for STI 0.6+ and keep vocals 3-6 dB above the band so the crowd's brain can lock on.
Keep the PA in stereo or use centre-fill so binaural ITD/ILD cues survive — mono kills the spotlight.
Control reverb: long RT60 and slap-back smear spatial cues — ring out and aim speakers off hard walls.
Use a de-esser and tight gating, not just more level — clarity beats loudness for being heard.
Everyday analogy
Like a torch in a dark crowded room: you don't make the whole room brighter, you point one beam at the one face you want and everything else stays dim.
Watch out
Myth: turn the vocal louder and people will hear it. Truth: it's selective focus, not louder ears — clarity (2-4 kHz, low reverb, stereo cues) lets the brain lock on far better than raw volume.
Fun fact
Your brain can swing the spotlight involuntarily: hearing your own name in an unattended conversation across the room grabs your attention about a third of the time.
Key takeaways
It's selective attention, not better hearing — your brain filters, your ears don't.
Two ears are the secret: timing (ITD) + level (ILD) differences locate the voice.
Clarity beats loudness — 2-4 kHz consonants and low reverb let the crowd lock on.
Mono, heavy reverb, and hearing loss all break the effect.
Pitch differences between voices make them easier to separate.