Piano stereo / spaced-pair phase — why grand piano L/R cancels body or hammer in mono
You placed a spaced pair over the strings, an XY at the hammers, a lid mic for bloom, maybe a spot on the low end. In headphones the stereo piano feels cinematic. Flip the piano bus to mono — body hollows, hammer attack softens, or the left–right image turns thin and nasal. That’s piano stereo phase, not a missing compressor or “brighter EQ.”
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PHIXER is free stereo phase-repair (VST3/CLAP/AU · Win/Mac/Linux) from Riverflux Audio. Frequency-aware phase rotation for L/R fights — not a polarity button, not a sample-nudger, not a widener. On grand piano, use only after polarity and mic timing are honest — skip when intentional width or a deliberate hammer/body split is the sound you want.
What piano stereo phase fights sound like
Classical, jazz, film, and pop piano tracks almost always use more than one mic. A spaced pair captures left–right boards; XY/ORTF catches hammer and midrange; a lid mic adds bloom; a low spot fills the left hand. Each capsule hears the same instrument from a different distance and angle. Stack them — or print a stereo bus — and mono summing reveals cancellations headphones hide.
Classic symptoms:
- Body / low-mid wood disappears in mono — warm and wide in cans; hollow when the piano bus collapses.
- Hammer attack softens or smears — sharp in stereo; dull or double-hit in mono.
- Spaced L vs R cancel mid board — overlapping midrange dies when L+R sum.
- Lid / spot vs main pair fights bloom — adding more lid subtracts body; blend knobs feel backwards.
- Stereo stems collapse on phones — Instagram, Bluetooth mono, laptop speakers fold the image.
Same physics as DI + mic dual-path fights, guitar dual-cab phase, and bass that disappears in mono: similar energy, different polarity/timing/spectrum, then destructive summing. Width tools do not fix that.
Why spaced pairs / lid + spot / L–R hammers fight
A grand piano is a large radiator. Sound leaves the soundboard, lid, and harp at different phases depending on capsule placement. A spaced pair (AB) often has several milliseconds of path difference L vs R — musical width in headphones, frequency-dependent cancellation when summed. XY pairs are cleaner on timing but still fight when you add a lid, hammer spot, or low close mic with a different arrival time and polarity.
Common setups that invite fights:
- Spaced AB over the strings — beautiful L/R image; mono often thins mid body where both mics share board resonance.
- XY or ORTF + lid / room — hammer clarity plus bloom; the distant mic arrives late and can cancel wood when blended hot.
- Main pair + undersoundboard / low spot — left-hand weight in headphones; polarity or path length often scoops that weight in mono.
- Hard-panned twin close mics — “stereo hammers” feel huge until mono reveals shared mid cancellation — same class as vocal doubles that thin when summed.
Mic choice and placement are features; phase fights are the tax. Name what disappeared (body, hammer, low board, lid air) before more EQ, compression, or an imager.
Why mono reveals them
In stereo, opposing-phase or delayed energy can still reach each ear as width. Sum L+R — phones, laptop mixes, TV downmixes, club systems that mono low-mid content, social-video playback — and those bands cancel. Piano body and hammer attack live where mono is unforgiving: low-mid wood and transient midrange. Check: each mic solo → blend in stereo → blend in mono. If the piano collapses, fix the mic stack before the master. Workflow: mono-check before/after.
Spaced pairs are especially revealing: “huge stereo piano” is often delay-based width. Legitimate artistry — until a mono listener loses the left-hand body you balanced for hours. Decide whether the mix must survive mono, then fix or consciously accept the tradeoff.
Honest order of fixes
1. Polarity first (Ø / Invert)
Hard 0° / 180° on secondary paths vs the reference (usually the main pair or the mic that carries the most body). Free and often enough. Flip the lid, the low spot, or one side of a spaced pair; listen in mono. Keep what restores wood and hammer weight without wrecking the stereo image you want. If one flip fixes it, stop. More: polarity invert vs phase rotation.
2. Time-align when one path is late / early
If waveforms show a clear lag at the hammer transient — lid vs XY, spot vs main, L vs R on a spaced pair — nudge the late path so attacks line up enough that mono stops cancelling body. Over-aligning every mic into identical spikes can kill the natural stereo depth of a grand; align for mono safety, leave musical room/path offset alone when it still passes mono. Details: phase repair vs time-align.
3. Frequency-aware phase rotation (PHIXER) when leftovers remain
After polarity and a reasonable align, some stereo piano buses still fight by band — body dies in mono while hammers survive, or low board thins while mid attack stays. That’s when spectral phase rotation helps: PHIXER rotates phase by frequency so more energy survives mono. It does not invent missing low end, replace better mic placement, or “fix” intentional width you chose on purpose.
Decision table
| You notice… | First try | Why |
|---|---|---|
| Invert lid / spot / one AB side and body returns | Polarity — done | Simple 180° mismatch between paths |
| Hammer transient clearly late on one mic | Time-align / nudge | Path-length / arrival offset |
| Align + polarity help some bands; others still die in mono | PHIXER on the stereo piano bus | Frequency-dependent residual fight |
| A mic sounds bad even solo | Move / swap mic / EQ / filter the take | Phase tools won’t fix a weak capsule placement |
| Mono is fine; you just want “wider” piano | Confirm mono first, then width carefully | Imagers ≠ phase repair |
| You want intentional spaced-pair width / phase as the sound | Don’t “repair” — own the tradeoff | Intentional stereo depth as tone control |
When frequency-aware phase repair helps on piano
- You’ve polarity-checked secondary mics, roughly aligned hammer attacks, and a band (often low-mid body or mid board) still collapses in mono.
- You printed a stereo piano stem (spaced AB bounce or processed stereo bus) and that file itself fights L/R.
- XY + lid (or main + spot) pass headphones but fail mono after basic alignment — same class as dual-mic fights on bass/guitar.
- Individual mics sound fine solo; only the blend cancels.
- Film / pop deliveries must survive TV and phone mono, and you need body back without killing the stereo image entirely.
PHIXER belongs on residual stereo / dual-path fights — not as the first plugin on every piano session.
When NOT to use PHIXER on piano
- Single mono piano mic — no L/R or dual-path phase to repair. Thin tone is placement, lid height, room, or EQ.
- Clear polarity only — if Ø on the lid or low spot restores mono body, stop. See polarity vs phase.
- Clear timing offset only — a lid a few ms late is nudge/delay (or move the stand), not rotation. See vs time-align.
- Intentional spaced-pair width / phase — classical/jazz often keep a slightly “imperfect” AB image because stereo depth is the record. Own that tradeoff; don’t “repair” it into lifeless mono perfection. Honest list: when not to use PHIXER.
- Intentional hammer vs body split — some pop/cinematic mixes leave a slight fight so attack stays sharp while body stays short.
- Using a stereo imager to “fix” cancellation — width tools don’t restore cancelled wood or hammer. See PHIXER vs imagers.
Short practical checklist
- Solo each mic (L, R, lid, spot). Listen for tone problems that aren’t phase.
- Blend the piano stack. Flip to mono. Note body / hammer / low board / lid air.
- Try polarity on secondary paths (lid, undersoundboard, one AB side, spot). Keep the best combo.
- If one hammer transient is late, nudge timing or adjust mic distance; re-check mono.
- If a band still cancels on a stereo or multi-mic stack, try PHIXER on the piano bus — then mono-check again.
- Only after mono is solid (or you consciously accept intentional width/phase), touch EQ, compression, or wideners. Imagers last.
- Then check how the fixed piano sits under vocals, strings, and drums — don’t fix the master first and ignore the piano group.
Order of operations: mic placement → polarity → time-align → frequency-aware phase repair → creative width / parallel. Skipping to an imager or “brighter EQ” on a cancelling piano stack is how hollow mono piano mixes ship to phones, TVs, and club PAs.
Related reading
- DI + mic / dual-mic phase fights — dual-path fights on bass/guitar
- Guitar dual-cab & multi-mic phase — same blend-knob / mono scoop pattern
- Vocal doubles phase — hard-panned twins that thin when summed
- Why bass disappears in mono — same mono-sum physics on low end
- Phase repair vs time-align — nudge first when attacks are late
- PHIXER vs stereo imagers — width ≠ cancelled-body repair
- Mono-check workflow — name what disappears before you fix
- Polarity invert vs phase rotation — 180° first on secondary piano mics
- When not to use PHIXER — skip intentional phase / wrong symptom
- PHIXER product page · Hub
Get the free fixer
PHIXER — free stereo phase-repair from Riverflux Audio (VST3/CLAP/AU · Win/Mac/Linux). No invented stats: try it on your spaced-pair / lid / XY+spot piano stack after the checklist above.