REAPER null test and phase align: invert polarity, align, null honestly, then residual spectral repair
REAPER is excellent at Invert, item nudge, and null tests. Use those first. Null tests lie under adaptive FX, so always mono-check the Master for listener fold. PHIXER belongs only after residual band-by-band L/R fights remain on stereo beds. Distinct DAW niche (not folk-instrument pages). Cross-links: polarity, vs time-align, null-test, when-not.
Download PHIXER free Watch tutorial
PHIXER is free stereo phase-repair (VST3/CLAP/AU · Win/Mac/Linux) from Riverflux Audio. Frequency-aware phase rotation for leftover L/R fights on stereo material. It is not a compressor, not a widener, and not a substitute for polarity invert, Utility mono, or delay align. Polarity and timing first; PHIXER after residual spectral fights.
What REAPER null-test / phase failure sounds like
- Invert polarity fixes nothing until you null. Two takes or dual mics look aligned, then Invert + sum still leaves a loud residual.
- JS or stock Phase Align moves help, then mono still hollows a band. Timing is closer, but L/R spectral fights remain on stereo beds.
- Null test "fails" because of FX, not phase. Adaptive processors, dither, and nonlinear FX never null cleanly. That does not mean mono fold is fine.
- Render / stem export thins vs monitoring. Fine on monitors, hollow on phone after bounce.
- Pair with the host-agnostic guide: DAW null-test + mono-check workflow.
Fast REAPER mono + null audition (about 90 seconds)
- Put a mono fold on the Master (JS Utility, channel mapper, or a dedicated mono plugin). Toggle it often.
- For a null test: duplicate the path, Invert polarity on the duplicate, sum both. Near-silence means near-identical. Loud residual means difference (timing, FX, or content).
- Solo pairs: DI vs mic, top vs bottom, close vs OH. Invert one, listen for body return before you chase EQ.
- Check correlation on Master, then mono fold with full mix muted vs open buses.
Order of operations in REAPER (before spectral phase rotation)
1. Invert polarity (stock or JS)
Flip one path when body or Mid returns immediately on a clear phrase. This is polarity, not "phase repair." Guide: polarity vs phase.
2. Phase align / item time offset
Use item nudge, take envelopes, or a phase-align helper to match arrival time. Prefer sample-accurate offsets over guessing with EQ. Cousin: vs time-align.
3. Honest null test (know the lies)
Null tests prove identity or isolate a processor change. They lie when dither, adaptive FX, lookahead, or nonlinear plugins are in the chain. Use nulls for dual-path identity. Use mono fold for listener fold-down.
4. One hero path to the bus
Do not leave every close, OH, and room all hot. Pick a Mid-safe hero, keep extras quieter. Parallel stacks are classic thin-body on phone fold.
5. Skip Haas and wideners before fold
Short-delay width makes headphones shimmer and phones hollow. Keep critical low-mid centered for render and stream.
6. Only then residual spectral repair with PHIXER
After Invert, align, hero levels, and an honest mono check, if a stereo bed still cancels by band, gentle frequency-aware rotation can help. Prove with mono A/B.
REAPER path types and typical failure modes
| Path | Common mono failure | First fix |
|---|---|---|
| Dual mic / DI+mic | Body cancels on Invert proof | Invert one; nudge item time |
| Null test never silences | Loud residual after Invert | Check FX/dither; null dry paths first |
| Phase align OK, mono still thin | Band-specific hollow | Hero levels; then PHIXER on stereo bed |
| Stem render vs monitor | Fine in room, thin on phone | Mono Master habit before render |
| Stereo FX return | Dry+wet comb on fold | stereo reverb mono |
REAPER checklist (to render)
1. Mono-check Master before every important render
Do not trust control-room stereo alone. Toggle mono on the delivery bus.
2. Null dry dual paths before FX
Prove polarity and timing on dry items first. Then add FX. Otherwise the null residual is mostly processing, not mic phase.
3. Label takes and routing
Name DI vs mic, top vs bottom, close vs OH so you know which Invert and which nudge you already tried.
4. Re-check after glue/render-in-place
Glue and render-in-place can change latency relationships. Invert and mono again after you commit.
When PHIXER helps in REAPER
- The material is already stereo and must stay stereo.
- Invert, item align, and hero levels are cleaned up, but mono still hollows a band.
- You can A/B mono with PHIXER bypassed and hear clearer body or Mid.
- You are not using it to replace Invert, item nudge, or to force a null test to silence adaptive FX.
Decision table
| You notice… | First try | Why |
|---|---|---|
| Body returns when you Invert one mic | Keep that Invert | Polarity fight |
| Null residual is huge with FX on | Null dry first | FX break identity nulls |
| Aligned but mono still hollow by band | PHIXER on stereo bed | Residual spectral L/R fight |
| Fine in room, thin on phone | Mono Master; pull extras | Monitor ≠ delivery fold |
| Mono source alone is dull | Tone / EQ / take choice | Not an L/R repair job |
When NOT to use PHIXER here
- You have not mono-auditioned Master yet.
- The fix is obviously Invert, item time offset, or quieter secondary.
- You want PHIXER to make a null test "pass" under nonlinear FX. Wrong job.
- The path is mono and the print problem is balance or EQ.
- See also when not to use PHIXER.
Quick path: Mono Master → Invert dual paths → item/phase align → honest null on dry paths → one hero image → skip Haas → PHIXER only for leftover stereo cancellation → mono again before render.
Related guides
- DAW null-test + mono-check workflow (host-agnostic)
- Polarity vs phase rotation
- Phase repair vs time align
- When not to use PHIXER
- Mono check before/after
- Correlation & phase meters
Watch
- PHIXER tutorial + how it sounds (walkthrough with audio examples)
- Short intro (no commentary)