11 · Dual rig PRO
Two full amps, two cabs, one plugin
Run two independent amp captures in parallel, each with its own mix panel, and blend two cabs — a two-mic blend on one amp, or a full cab per amp.
Dual amp rig — a level/pan/phase mixer under each head.
Dual cab — two-mic IR blend with per-mic level, pan and phase.
The plugin is mono-in by design; the stereo image is created intentionally inside the box. Engaging dual mode pans the two amps hard left and right by default — the right way to run a dual rig (a wide, dimensional tone, each amp on its own side). Summing two amps to the centre instead phase-cancels the low end, so the plugin warns you if both land near centre or if the two captures have different native sample rates.
Why a dual rig is panned, never summed — the measurements
Two nonlinear amp captures must never be summed onto one channel. We measured it on the real audio engine (the internal DspProbe --dual harness, driving the actual mixer with noise and reading back the spectrum) and found two independent things go wrong when two amps share a channel:
- Low-end phase cancellation. Two different captures partially cancel where their phase disagrees — measured at −16 dB at 80 Hz and −4 dB at 120 Hz. That hollowed-out low end is the classic "thin dual" tone. It happens at any pan while both amps share a channel, and a mono sum can never escape it.
- Midrange comb filtering. Every capture carries its own native sample rate; two branches at different rates end up a few samples apart in time. Summed, that comb-filters the 1–6 kHz midrange by 30–50 dB — a phasey, hollow mid on top of the thin bass.
Panned hard left and right, neither mechanism can fire: each amp lands on its own channel, so there is nothing to cancel or comb against. Measured that way each side is identical to that amp running solo (0.0 dB difference across the spectrum) — the second amp adds stereo width and depth, not a tonal fight. That is why the plugin spreads the amps hard L/R the instant you go dual, nudges you with a warning if they drift back toward centre, and — as below — renders a dual amp rig to two separate files rather than one blend.
Render Rig — what a dual rig exports
Render Rig bakes the live rig into a standard .nam. Because a .nam is mono in and out, what it writes depends on the rig:
- Single amp → one profile, as before.
- Dual amps → two profiles, "…L" and "…R" (one per head). Each is rendered in isolation — no summing, and no pan baked in — so the two files stay clean. Load them back into a dual rig, or into two slots of NAM-compatible hardware, and the exact stereo tone survives: no width lost, nothing cancelled.
- One amp through dual cabs → one profile. Cab convolution is linear, so a two-mic IR blend bakes cleanly into a single file — exactly how commercial blended IRs ship. (A dual amp and dual cab still splits L/R, each head taking its own cab.)
IR alignment — automatic, plus a fine trim
Blending two IRs has its own classic failure mode: every IR carries its own leading dead time (mic distance, processing padding), and two IRs whose impulses don't land at the same instant comb-filter when summed — the same hollow sound, from the cab side. Hardware modelers ship an "align" control in their cab blocks for exactly this reason.
NAM 9000 handles it in two layers:
- Automatic onset alignment (everyone). Every IR is scanned at load and shifted so its impulse starts at the exact same position. Two IRs that would have combed — measured on our engine, a 37-sample offset notches the blend by −21 dB — sum to a 0.0 dB-ripple flat blend after alignment. You never touch anything.
- ALIGN micro-delay (Pro). A ±2 ms knob on the IR B rail nudges one mic against the other (positive delays B, negative delays A) — the by-ear fine trim for creative mic-distance effects or IRs whose tonal centers sit later than their onsets. Sample-accurate, verified against the theoretical comb positions.
If a blend still thins out, the per-mic phase button (Ø) flips polarity — alignment fixes timing, Ø fixes polarity; together they cover both ways two mics can fight. All of it applies before Render Rig bakes a blend, so exported profiles are phase-true too.
