The Crowd Is Too Loud

Phase Reversal: The Audio Engineering Trick That Silences Crowd Noise

Intro

Have you ever listened to a sportscaster calling a basketball game right beside the roaring fans? Despite the yelling, clapping, and booing, you can still hear every word clearly. That’s not magic—it’s audio engineering. The secret is a technique called phase reversal.

What Is Phase Reversal?

Phase reversal is a microphone setup that cancels out unwanted background noise while keeping the announcer or singer’s voice front and center. Here’s how it works:

• Primary microphone (Mic A): Positioned close to the announcer’s mouth.

• Secondary microphone (Mic B): Placed 8–10 inches away, wired out of phase with Mic A.

• Result: Both mics pick up the crowd equally, but only Mic A captures the announcer’s voice directly. When combined, the crowd noise cancels itself out.

The Math Behind It

Think of it in decibels:

• Crowd noise enters both mics at +10 dB.

• The secondary mic flips the signal to –10 dB.

• When combined, +10 and –10 equal 0 dB—effectively silencing the crowd.

Meanwhile, Mic A still delivers the announcer’s voice, clean and clear.

How to Use Phase Reversal

• Live broadcast: Feed both mics into the same channel. Start with Mic A, then slowly raise the fader on Mic B until the crowd fades away.

• Studio mixdown: You can introduce the secondary signal anywhere in the mix. It’s not as powerful as live use, but still effective.

Pro Tip

If you build a special cable for the secondary mic, label it clearly. You don’t want phase reversal kicking in when it’s not needed.