Bass DI + amp/cab phase: why dual-path low end cancels in mono
You reamped a DI through an amp (or cab IR), blended both for weight and grit, and the headphones smile. Flip to mono, or listen on a phone, and the fundamental thins, the note attack softens, or the whole bass feels like it stepped behind a curtain. That is dual-path phase (and polarity), not "you need more 80 Hz 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 leftover L/R fights on stereo material. It is not a bass enhancer, not a DI reamp, and not a substitute for flipping polarity or nudging delay on one path. On bass DI + amp, use it only after polarity and timing are honest.
What DI + amp/cab phase fights sound like
- Fundamental disappears in mono. Headphones keep the DI punch and cab body separate enough; mono sum cancels shared low energy.
- Note attacks go soft. Transient peaks on DI and mic arrive offset; summed attack loses click or pick definition.
- Cab IR + DI feels huge until phone check. Impulse responses add path length; the blend that "sounds expensive" collapses on fold-down.
- Amp sim wet + DI dry cancels mid-bass. Same note, different latency and filter curves, destructive when summed.
- Live DI + stage mic bleed fights the printed DI. Room mic under bass DI is a quieter dual path with room delay.
Same physics as classic DI + mic phase and the broader why bass disappears in mono story: similar energy on two paths, then destructive summing. Bass just puts the failure right where mono platforms hurt most (phones, club PA mono, YouTube fold).
Why DI and amp/cab paths fight
A DI captures the instrument almost instantly. An amp mic, cab mic, or amp-sim IR hears the same note after speaker, room, or convolution delay, plus polarity orientation of the capsule and the amp's own phase shifts by frequency. When you blend both for "solid DI + character cab," you are stacking near-copies with timing and polarity offsets. Headphones forgive a lot. Mono sum does not.
Amp sims and IR loaders often add a few samples to tens of milliseconds of latency relative to the dry DI. That is timing first, spectral phase second. If you widen the bass bus before fixing that, you usually make mono worse. See phase repair vs time-align.
Honest order of fixes
1. Polarity on one path
Solo DI + amp (or cab mic). Flip Ø on the amp/cab path. If low-end body returns and mono thickens, keep it. Stop there when that is enough. Polarity invert vs phase rotation.
2. Timing / delay match
Zoom the transient. Nudge the amp/cab (or IR wet) so the attack lines up with the DI. Match samples or milliseconds, not "feel." Latency from amp sims and IRs is delay, not a reason to open a widener.
3. Level and EQ role split
Often DI owns the solid mid-fundamental; cab owns grit and top. High-pass the cab gently, or low-pass the DI grit band, so they share less overlapping energy. Less overlap means less cancellation when summed.
4. Mono-check the blend early
Fold to mono (or use a mono button) on every DI+amp change. Watch a correlation / phase meter if you have one. Correlation and phase meters warn; they do not fix.
5. PHIXER only on residual stereo fights
After polarity + timing + role split, if a printed stereo bass bus (or stereo IR + stereo DI stack) still cancels by band in mono, frequency-aware phase rotation can help that stereo file. Skip pure mono DI stems. There is nothing for L/R repair to do. When not to use PHIXER.
Decision table
| You notice… | First try | Why |
|---|---|---|
| Ø on amp/cab restores fundamental | Keep polarity | 180° mismatch |
| Nudging IR/amp aligns attack with DI | Timing / latency | Delay, not spectral fight |
| Both paths share the same 60–120 Hz lump | Role-split EQ / levels | Overlapping energy cancels |
| Stereo bass bus still band-cancels after hygiene | PHIXER on that stereo bus | Residual spectral L/R fight |
| Single mono DI track sounds thin | Tone / arrangement, not PHIXER | No L/R relationship |
Practical DI + amp/cab workflow
- Print or route DI and amp/cab on separate tracks (or clean DI + wet amp-sim).
- Solo both. Flip mono. Note what thins.
- Try polarity on the amp/cab path.
- Align timing at the first transient (pick or finger attack).
- Carve overlapping lows so one path owns the fundamental.
- If a stereo bus still band-cancels, try PHIXER, then mono-check again.
- Only then add saturation, compression, or gentle width (and re-check mono).
When frequency-aware phase repair helps
- You aligned polarity and delay, but a stereo bass bus still loses body in mono on specific bands.
- Stereo cab IRs or dual amp-sim paths still fight after role-split EQ.
- A printed stereo bass stem (DI+cab already bounced) arrives late in the mix with leftover L/R cancellation.
PHIXER does not replace a good reamp, fix a weak DI level, or invent missing sub. It is residual stereo repair, same honesty as the rest of the PHIXER guides.
When NOT to use PHIXER on bass DI + amp
- Mono DI only. No L/R relationship to repair.
- Clear polarity or delay fix. Stop when Ø or nudge restores the fundamental.
- "More width on the bass bus" to hide the hollow. That usually worsens mono. Fix correlation first.
- Missing notes from arrangement or a high-pass too aggressive. Wrong tool.
Order of operations: polarity on one path → timing / IR latency align → role-split EQ and levels → mono-check → frequency-aware phase repair on residual stereo → creative width last (if at all). Skipping to "stereo image the bass" is how phone mixes lose the low end.
Related reading
- DI + mic phase (bass/guitar dual-path capture)
- Why bass disappears in mono
- Polarity invert vs phase rotation
- Phase repair vs time-align
- Correlation and phase meters
- When not to use PHIXER
- Product · Hub
Get the free fixer
PHIXER is free stereo phase-repair from Riverflux Audio (VST3/CLAP/AU · Win/Mac/Linux). Try it on residual stereo bass buses after polarity and timing, not as a substitute for Ø or delay matching.