Understanding Phase Correlation

Phase correlation describes the relationship between the left and right channels of a stereo signal. Understanding this relationship is crucial for mixing, mastering, and understanding how audio behaves in different playback scenarios.

When identical signals are sent to both speakers (correlated audio with same polarity), the sound waves reinforce each other and create a phantom center - the perception of sound coming from directly between the speakers. This is how centered vocals and instruments are typically reproduced in stereo.

If one channel's polarity is inverted (flipped), the waves now oppose each other. For perfectly correlated content, this creates a Phantom L/R effect - sounds that exist equally in both speakers cancel out in the center, and the remaining audio appears to come from the left and right speakers themselves rather than between them. If such a signal were summed to mono, the correlated content would cancel completely.

With uncorrelated audio (independent left and right content), polarity inversion has no perceptible effect because there's no consistent phase relationship to disrupt. The sound simply appears diffuse, coming from both speakers without a clear center image.

The correlation meter visualizes this relationship in real-time:

• +1 = Perfectly correlated (mono compatible)
• 0 = Uncorrelated (independent L/R)
• -1 = Out of phase (will cancel in mono)

Try the following exercises to develop your understanding of phase correlation:

1. Listen to each scenario with pink noise: Start with "Correlated + Same Polarity" and notice how the sound appears centered between your speakers. Then switch to "Correlated + Inverted Polarity" - notice how the center image disappears and sound seems to come from the speakers themselves.
2. Compare uncorrelated scenarios: Switch between the two uncorrelated options. Can you hear any difference? You shouldn't - because there's no correlation to disrupt, polarity inversion has no effect.
3. Watch the correlation meter: As you switch between scenarios, observe how the meter reading changes. Correlated audio with same polarity shows +1, inverted shows -1, and uncorrelated hovers around 0.
4. Upload your own music: Try a track with a strong center vocal or kick drum. Switch to inverted polarity - what happens to the centered elements? This demonstrates what would happen if one speaker wire were connected backwards.
5. Test mono compatibility: Click the "Mono" button to sum L+R. With "Correlated + Inverted" selected, the audio should completely cancel - demonstrating why phase correlation matters for mono playback (phone speakers, club systems, etc.).