Understanding Phase
The Relationship Between Waves
Visual: Two sine waves showing in-phase, out-of-phase, and partial phase relationships
Phase describes where a wave is in its cycle at any given moment.
0° = Perfectly in sync (in phase)
180° = Perfectly opposite (out of phase)
90° = Quarter cycle offset
What Happens When Waves Combine:
Why This Matters:
Every sound you record or process creates phase relationships with other sounds. Understanding phase helps you:
Diagnose thin/hollow sounds
Fix multi-mic recordings
Avoid problematic processing
Create intentional width effects
Imagine two people swinging jump ropes. If they swing in sync, the ropes reinforce each other. If one is early and one late, they collide and cancel out.
Phase is measured in degrees:| Phase Relationship | Result |
|---|---|
| 0° (in phase) | Double the amplitude (+6dB) |
| 90° | 1.4x amplitude (+3dB) |
| 180° (out of phase) | Complete cancellation (silence) |
| Between | Partial reinforcement/cancellation |
When peaks meet troughs, sound disappears — this is phase cancellation.
Common Causes:
Multi-microphone Recording:
- Sound reaches each mic at different times
- The time difference creates phase offset
- Some frequencies cancel, others reinforce
Stereo Miking Techniques:
- Distance between mics creates timing differences
- Summed to mono = cancellation issues
Direct + Room Sound:
- DI recording + amp mic
- Direct signal vs mic signal timing
Processing with Phase Shift:
- Certain EQs shift phase
- Some plugins add latency
- Parallel processing without alignment
Symptoms of Phase Cancellation:
Sound is thin or hollow
Missing low frequencies
Sound "moves" when panned
Worse in mono than stereo
Sounds "inside your head" on headphones
The Snare Test:
If your snare sounds weak and papery, phase cancellation between top and bottom mic is often the culprit.
Comb filtering is partial phase cancellation — it's everywhere and often the enemy.
What is Comb Filtering?
When a sound and its delayed copy combine, some frequencies reinforce and others cancel, creating a pattern that looks like a comb.
The Math:
Cancellation occurs at frequencies where the delay equals half a wavelength:
1ms delay Cancellation at 500Hz, 1.5kHz, 2.5kHz...
2ms delay Cancellation at 250Hz, 750Hz, 1.25kHz...
Visual:
Reflections from nearby surfaces
Multi-mic setups (drums, piano)
Direct + reverb signals
Chorus and flanger effects (intentional!)
Double-tracking too tight
Comb Filtering vs. Flanging:
Flanging IS comb filtering with the delay time modulating. Same principle, used creatively.
Frequency Response with Comb Filtering:
│ ╱╲ ╱╲ ╱╲ ╱╲
dB │ ╱ ╲ ╱ ╲ ╱ ╲ ╱ ╲
│╱ ╲╱ ╲╱ ╲╱ ╲
└──────────────────────── Hz
Polarity flip is instant 180° phase shift — sometimes the fix is that simple.
Phase vs. Polarity:
Phase = Time relationship (can be any angle)
Polarity = Instant flip (0° or 180° only)
When to Flip Polarity:
Snare Bottom Mic:
- Bottom mic captures the snare from below
- Wires are moving away as top head moves toward
- Flip polarity on bottom mic to align
Bass DI + Amp:
- Different signal paths = different timing
- Try flipping one, listen for fuller bass
Two Mics on Same Source:
- One closer, one farther
- Flip the farther one, test improvement
How to Test:
Solo both tracks together
Flip polarity on one track
Listen for which setting has more low end
The fuller sound = correct polarity
Every DAW has a polarity flip:
Often a "Ø" or "φ" button
Also called "phase invert" (technically incorrect)
It's instant — no processing needed
Rule of Thumb:
When two mics capture the same source, always test polarity flip.