Multi‑mic drum recordings can suffer phase cancellation when timing or polarity is off. That usually means weak kick, hollow snare, or blurry stereo. Here is a practical way to align phase without losing punch.
Symptoms of phase issues
- Low‑end disappears when overheads are added.
- Snare loses body when room mics are on.
- The mix sounds better in mono.
- Correlation meter drops into negative values.
Why phase shifts happen
Each mic sits at a different distance from the drum head. That timing difference shifts phase and changes the sum. Polarity flips or un‑compensated latency can make it worse.
- Distance differences between microphones.
- Polarity inversion in preamps or plugins.
- Latency from external processing.
How to measure and align
- Listen in mono and identify the cancellations.
- Use a correlation meter to see the phase offset.
- Try polarity inversion on kick or snare.
- Nudge samples until low‑end and punch return.
How Piroola handles it
S2_GROUP_PHASE_DRUMS.py analyzes drum stems and computes correlation. The stage applies time alignment and polarity correction to maximize drum‑bus coherence without changing balance.
- Detects problematic pairs in kick, snare, and overheads.
- Applies sample‑level offsets.
- Validates coherence with phase metrics.
Manual workflow
- Check kick + overheads in mono.
- Flip polarity where low‑end collapses.
- Align main transients in a sample editor.
- Repeat with snare and room mics.
Common mistakes
- Trusting waveforms over your ears.
- Aligning everything to the same point without groove context.
- Forgetting polarity checks before nudging.
Checklist
- Stable, positive correlation.
- Solid low‑end in mono.
- Clear transients without flanging artifacts.
