Focusrite Scarlett 2i2: Line vs Instrument Input — When to Use Each

TL;DR: Use INST (Instrument/Hi-Z) for a guitar or bass plugged in directly with a ¼″ cable. Use LINE for a keyboard, synth, drum machine, or the output of an external preamp or mixer. Using the wrong setting causes either a thin, weak signal (if you use LINE for guitar) or a distorted, overloaded signal (if you use INST for line-level gear).

What the Line/Inst Switch Actually Does

The switch changes the input impedance and expected signal level of the combo input. INST (instrument mode) presents ~1 MΩ impedance at low sensitivity — correct for a passive guitar or bass pickup. LINE presents ~10 kΩ impedance at higher sensitivity — correct for gear that outputs a standard +4 dBu or −10 dBV signal.

On the Focusrite Scarlett 2i2 4th Gen, each combo input has a dedicated LINE/INST button on the front panel. The button is per-channel — you can set Input 1 to INST and Input 2 to LINE simultaneously if needed.

Setting	Input Impedance	Expected Signal Level	Use For
INST	~1 MΩ (Hi-Z)	Low (passive pickup)	Guitar, bass (direct)
LINE	~10 kΩ	Hot (line level)	Keyboard, synth, DI box output, external preamp

Guitar and Bass: Always Use INST

If you’re plugging a guitar or bass directly into the 2i2 with a ¼″ cable, use INST. Passive pickups on electric guitars and basses produce a high-impedance, low-level signal. Connecting to a LINE input loads the pickups — it lowers the effective impedance the pickup “sees” — which rolls off high-frequency response and kills your tone.

What you’ll hear if you use LINE for guitar by mistake:

Thin, muffled sound with reduced treble
Lower output level requiring more gain
Loss of the pick attack and string definition that INST preserves

The 2i2’s INST mode presents ~1 MΩ. Most passive guitar pickups are designed to work into 1 MΩ loads — this is what a tube amp’s input stage presents, and why amps sound different from interfaces that get the impedance wrong.

Exception: If you’re running guitar through a DI box first, plug the DI box’s XLR output into the combo input as a microphone-level signal (phantom power off), or use its ¼″ thru/output into LINE mode if the DI has a buffered output. A DI box converts the high-impedance signal before it reaches the interface — the INST input is no longer needed.

Keyboards, Synths, and Line-Level Gear: Use LINE

Keyboards, synthesizers, drum machines, and the output of external mixers or preamps all run at line level — a much hotter signal than a passive guitar pickup. Use LINE for these sources. Connecting them to INST will drive the input into clipping even at low gain knob settings.

What you’ll hear if you use INST for a keyboard by mistake:

Distortion or clipping even at low gain knob positions
Signal that clips the meters immediately
No clean headroom for dynamics

Line-level gear typically outputs at −10 dBV (consumer) or +4 dBu (pro). Both are orders of magnitude hotter than a passive pickup. The LINE input expects this level; the INST input does not.

Active Pickups and Active Basses

Active pickups (common on basses, some guitars) include an onboard preamp that boosts the signal. They still have relatively high output impedance compared to true line-level gear — INST mode is still correct for most active basses. If you get clipping on INST with an active bass, try reducing your instrument’s volume slightly before reaching for the LINE setting.

If the input still clips with gain at minimum on INST mode, a DI box between the instrument and interface solves it cleanly by attenuating the signal before it hits the combo input.

The 2i2 4th Gen Per-Channel Phantom Power Note

On the 4th Gen 2i2, phantom power (48V) is per channel. If you’re running a condenser microphone on Input 1 and a guitar DI on Input 2, you can enable phantom only on Input 1. This matters for ribbon microphones — phantom power on the wrong channel can damage a ribbon. The Scarlett Solo has global phantom power (both inputs together), which makes this mix impossible on that model.

Quick Reference

Source	Correct Setting
Electric guitar (passive)	INST
Electric bass (passive)	INST
Electric bass (active, most)	INST
Acoustic guitar (via pickup or DI box)	INST or LINE — see DI box output type
Keyboard / synth	LINE
Drum machine / sampler	LINE
External preamp output	LINE
Mixer output	LINE
DI box XLR output	XLR combo input (mic-level), no INST/LINE switch applies

→ See also

Editorial methodology: Assessments are based on manufacturer specifications and editorial research. Full editorial policy · Affiliate disclosure