Cabs and IRs
What an impulse response actually is, how one gets onto the Helix LT, and why someone else's preset can load perfectly and still sound like the wrong cabinet.
What an IR is
An impulse response is a recording of what a mic'd speaker cabinet does to a sound. Someone plays a frequency sweep through a real cab, records it, and mathematically removes the sweep — what is left is the cabinet's fingerprint, which can then be applied to anything. It is the same idea as a convolution reverb, with a much shorter decay. In practice: it is a photograph of a specific speaker, in a specific room, with a specific mic in a specific place.
Cab block or IR block?
A Cab block is Line 6's own speaker model, with a mic you can change and parameters you can move. An IR block plays back a file instead — someone else's photograph, with far less to adjust but a huge library to choose from. Neither is better. Cab blocks are easier to steer; IRs are how you get a specific commercial cab that Line 6 do not model. What matters is that you use ONE of them, and only when you are going into something full-range.
Helix LT 3.80 Owner's Manual · HX Edit Pilot's Guide 3.80IRs are addressed by slot number, not by name
This is the whole reason downloaded presets sound wrong. A preset does not carry its IR — it stores "IR 12", and on your unit slot 12 holds whatever you put there. The preset loads without an error and sounds like a different cabinet, or like nothing at all. When you install someone's preset pack, install their IRs into the slots they specify. And when you reorganise your own library, every preset pointing at the moved slots quietly follows the number, not the file.
Loading an IR
IRs do not arrive by USB stick or SD card. They go on through HX Edit, into a library of 128 numbered slots that lives on the unit.
- 1
Open HX Edit's IRs tab
It starts empty — the library ships with nothing in it, which surprises people who expect factory IRs. The list shows 128 index numbers down the left.
- 2
Pick the slot you want, then Import
Select an index location first, then Import, and choose your file. Dragging several files in at once works too — they fill from the slot you had selected, downwards.
- 3
It takes .wav or .hir
.hir is Line 6's own format and is what Marketplace IRs come as. Everything else in the world ships .wav, and any .wav imports regardless of its bit depth, length or sample rate. One caution: import files that were actually made as IRs. Any other audio file will import happily and sound like nothing you wanted.
- 4
Point an IR block at it
Add a Single IR or Dual IR block and set IR Select to the index you loaded. A Single IR block can be 1024-sample or the higher-resolution 2048; a Dual holds two IRs in one block with their own pan, polarity and up to 50 ms of delay between them.
You cannot reorder the library
There is no move operation and no drag-to-reorder. Rearranging means copy, paste and clear, one slot at a time — which, given that presets reference slot numbers, is a job worth doing once and carefully rather than casually.
Everything is converted on the way in
Whatever you import, it becomes 48 kHz, 32-bit, mono, 2048 samples on the device. For a stereo WAV you can choose in HX Edit's Preferences whether it takes the left channel, the right, or a mix of both — worth setting deliberately if you bought a stereo pack.
Marketplace IRs need an authorised computer
Premium .hir files show a gold guitar-pick badge in the list. Importing or exporting them requires your computer to be authorised and your Line 6 account signed in — once they are on the unit, no internet is needed to play them. Exporting also converts back: a Marketplace IR saves as .hir, and anything you imported as .wav saves as .wav.
Back the library up with everything else
The IR library is included in an HX Edit backup, so the same one-minute Create Backup that protects your presets protects the IRs those presets are pointing at. Given how the slot-number trap works, backing up one without the other is barely a backup.
IR blocks cost less DSP than Legacy cabs
From firmware 3.50 the IR-based blocks are significantly cheaper than the original Legacy Cab blocks. If a preset will not fit, swapping a Legacy cab for an IR or a newer Cab block is often the single biggest saving on the board.