If you’ve already read our walkthrough on turning a Raspberry Pi into a real-time guitar amp modeler, you know the software side is mostly sorted. NAM 0.7.x runs on a Pi 5 with acceptable latency, GuitarML Proteus handles lighter models well on a Pi 4, and Aida-X sits somewhere in the middle. What that post doesn’t spend much time on is the piece that makes or breaks the whole rig before you even load a model: the USB audio interface.
A bad interface choice wastes everything downstream. You can have the cleanest NAM capture in the world and still sound like a cassette recording through a Behringer UCA222 into a Pi 4 with a poorly tuned ALSA configuration. This guide is for people who want to skip the trial and error.
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A Few Ground Rules Before We Start
All latency numbers below were measured on a Raspberry Pi 5 (BCM2712, 2.4 GHz) running Raspberry Pi OS Bookworm 64-bit, with JACK 1.9.22 and pipewire-jack as the backend. Where noted, Pi 4 (BCM2711) numbers are also included because a lot of people are still running those. Round-trip latency (RTL) is measured with jack_iodelay — that’s input-to-output through the full signal chain, not just buffer math. Models tested were NAM 0.7.3 running a standard LSTM capture, and Aida-X running a medium-complexity model.
Phantom power listings are accurate as of May 2026 firmware. CAD pricing is approximate street price from major Canadian retailers as of this writing — assume ±10% depending on the day.
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The Interfaces
Focusrite Scarlett Solo 4th Gen
~$149 CAD
The Solo is the entry point to Focusrite’s current lineup and it’s the interface I’d hand to someone building their first Pi guitar rig without hesitation — with one caveat we’ll get to.
ALSA support on Pi OS Bookworm is plug-and-play. The 4th Gen Scarlett series uses a standard USB Audio Class 2.0 implementation, so aplay -l finds it immediately with zero config. No fussing with udev rules, no manual module loading. That alone separates it from a lot of cheaper options.
Real-world RTL at 64 samples: 8.2 ms on Pi 5, 9.6 ms on Pi 4. At 128 samples: 11.4 ms (Pi 5), 13.1 ms (Pi 4).
That 64-sample figure on the Pi 5 is genuinely playable for clean and crunch tones. Running NAM with an LSTM model at 64 samples is stable on Pi 5. On Pi 4, you’ll get dropouts under heavy sustained chords — palm-muted chugging on a drop-tuned guitar will clip the CPU headroom and you’ll hear it. Budget an extra 10–15% buffer on the Pi 4 or switch to a lighter model format like the standard feedforward NAM captures rather than LSTM.
The preamp on the Solo is Focusrite’s “Air” circuit (switchable), which adds a subtle high-frequency lift. For guitar direct-in, you probably won’t care — you’re bypassing the preamp character with your amp model anyway. But if you ever want to throw a condenser mic on a cabinet, the Solo does provide 48V phantom power.
Sample rate ceiling: 192 kHz. You won’t use it for amp modeling (48 kHz is standard), but it’s there.
Build quality is the usual Focusrite mix — solid enough, but the gain knobs have a slight plasticky feel compared to the MOTU M2. It’ll survive desktop use without issue.
Best for: First Pi guitar rig, anyone who wants reliable driver support and doesn’t want to troubleshoot.
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Focusrite Scarlett 2i2 4th Gen
~$199 CAD
Everything I said about the Solo applies here, plus a second input and output. The 2i2 shares the same USB Audio Class 2.0 implementation, same ALSA compatibility, same 192 kHz ceiling.
RTL is nearly identical to the Solo — within 0.3 ms in controlled testing, which is within measurement noise. You’re not buying the 2i2 for lower latency.
What you’re buying is flexibility. Two instrument/mic inputs means you can run a wet/dry rig — direct guitar on one channel, a processed monitor mix on the other. You can also record a dry track for re-amping while monitoring through your Pi model simultaneously. If you’re running a Pi-based rig as part of a home recording setup and not just a stage/practice amp modeler, the second channel is actually useful.
The 2i2 also has hardware-monitored direct monitoring, which you can use to mix dry signal with processed output to manage perceived latency. It’s not a substitute for actually lowering RTL, but it helps for players who are sensitive to delay.
Phantom power: yes, 48V, on both channels.
Best for: Anyone who wants a second input for recording, wet/dry setups, or occasionally running a condenser mic alongside the guitar.
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Behringer UCA222
~$39 CAD
The UCA222 is the interface people buy because it’s forty dollars. Let’s be honest about what you’re getting.
Driver support: USB Audio Class 1.0, which means it works — but you’re capped at 48 kHz/16-bit. No 24-bit recording. This matters less for amp modeling monitoring than it does for final recording quality, but it is a real ceiling.
RTL at 64 samples: 14.8 ms on Pi 5, 18.2 ms on Pi 4. At 128 samples: 22.4 ms (Pi 5), 26.7 ms (Pi 4).
Those numbers are bad. 22 ms round-trip is the threshold where most players start to notice the delay as a distinct slap, not just a slightly fuzzy feel. At 26.7 ms on Pi 4 at 128 samples, you will feel the latency as a performance problem. This thing is not suitable for real-time amp modeling if you care about playing feel.
The analog I/O is RCA, not TRS or XLR. You need a 6.35mm-to-RCA cable or adapter to use a guitar with it. That’s a noise risk and an impedance mismatch depending on what you’re plugging into it.
No phantom power. No instrument-level input (technically — the RCA inputs will accept line-level signals).
Build quality is exactly what $39 buys. The chassis flexes.
Best for: Budget-constrained people who want to experiment with the software chain before committing money, or applications where latency genuinely doesn’t matter (offline processing, recording without monitoring).
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Behringer UMC22
~$59 CAD
The UMC22 is the one I’d actually recommend if someone absolutely needs to stay under $75 CAD. It’s a significant step up from the UCA222 without costing much more.
USB Audio Class 1.0 again, so 48 kHz/16-bit ceiling — same limitation as the UCA222. Driver support is plug-and-play on Pi OS Bookworm, though I’ve seen occasional issues with USB 3.0 port assignment on Pi 5; using a USB 2.0 port resolved it in every case I’ve encountered.
RTL at 64 samples: 11.9 ms (Pi 5), 14.3 ms (Pi 4). At 128 samples: 16.2 ms (Pi 5), 19.8 ms (Pi 4).
That’s a meaningful improvement over the UCA222, and 11.9 ms on Pi 5 at 64 samples is on the edge of playable — not great, but not obviously broken. Running NAM 0.7.3 on Pi 5 at 64 samples through the UMC22 is functional for bedroom practice. I wouldn’t take it to a stage.
The UMC22 has an actual XLR/TRS combo jack with a MIDAS-designed preamp (Behringer’s words) and a proper instrument input with a -20 dB pad. It will run a condenser mic with 48V phantom power — which is wild for $59, and works.
Build quality is slightly better than the UCA222, though the gain knob has notable channel variation at lower settings (common on budget preamps — you’ll notice it if you’re critically listening at low volumes).
Best for: Tightest budget that still wants a usable amp modeling experience, condenser mic on a cheap rig.
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MOTU M2
~$229 CAD
The MOTU M2 is where things get noticeably better, and it’s worth the price jump if you’re building a serious rig.
USB Audio Class 2.0, works immediately on Pi OS Bookworm. No quirks, no config, shows up in ALSA as you’d expect.
RTL at 64 samples: 6.8 ms on Pi 5, 8.1 ms on Pi 4. That is the lowest round-trip latency I’ve measured from any interface in this roundup on Pi hardware. At 128 samples: 9.3 ms (Pi 5), 11.4 ms (Pi 4).
The 6.8 ms figure deserves attention. Running NAM 0.7.3 with a standard feedforward capture on Pi 5 through the M2 at 64 samples, you are in the zone where most players can’t distinguish model latency from a real amp in a room. It’s not zero, but it doesn’t feel like a liability.
The M2’s DAC quality is also a step above everything else in this list — it measures exceptionally flat and the output is clean enough that you’ll hear the difference on headphones. If you’re doing any kind of critical listening or recording alongside your amp modeling rig, the M2’s monitoring circuit is noticeably better than the Focusrite options.
Two combo XLR/TRS inputs, 48V phantom on both, front-panel meters with real signal LEDs, and a solid metal chassis that feels like it belongs on a desk, not in a parts bin.
192 kHz sample rate ceiling.
One thing to flag: the M2 occasionally needs a powered USB hub on Pi 5 under high USB bus load. If you’ve got a keyboard, mouse, and a USB SSD all hanging off the same Pi, add a powered hub. I’ve never had issues on a dedicated amp modeling Pi (minimal other USB peripherals), but it’s worth knowing.
Best for: Anyone who wants the lowest latency in this group, best audio quality, or is running a hybrid recording/amp-modeling setup.
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Audient EVO 4
~$169 CAD
The EVO 4 is Audient’s budget line and it punches above its price in a couple of specific ways, while having one real limitation worth knowing about.
USB Audio Class 2.0. Pi OS Bookworm compatibility is clean — no issues. 48 kHz/24-bit is the practical ceiling for amp modeling use; it technically supports 96 kHz but I observed occasional sample-rate negotiation failures at 96 kHz on Pi 5 with JACK, which I didn’t see on the Focusrite or MOTU units. At 48 kHz it’s rock solid.
RTL at 64 samples: 7.9 ms (Pi 5), 9.3 ms (Pi 4). At 128 samples: 10.8 ms (Pi 5), 12.6 ms (Pi 4).
Those are strong numbers, second only to the MOTU M2 in this roundup. The EVO 4’s preamp is based on Audient’s console circuit heritage and the input sounds noticeably cleaner than the Focusrite Scarlett preamps — less hyped, more neutral. For a modeler, where you want your NAM or Aida-X capture to define the character, that neutrality is actually a feature.
The EVO 4 has Audient’s “Smartgain” feature which auto-sets input gain. On Pi, you’re generally setting ALSA input levels manually anyway, so Smartgain mostly just sits there, but it’s not harmful.
48V phantom power on both channels.
Build quality is a step above the Behringer options, roughly comparable to the Scarlett 2i2 — solid but not as premium-feeling as the MOTU M2.
Best for: Players who want Focusrite-level reliability with slightly cleaner preamps, or who care about the quality of any acoustic/vocal recording they do alongside their guitar rig.
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Comparison Summary
| Interface | RTL @ 64s (Pi 5) | RTL @ 128s (Pi 5) | Phantom | Max Rate | ~CAD | ALSA OOB | |—|—|—|—|—|—|—| | Focusrite Scarlett Solo 4th Gen | 8.2 ms | 11.4 ms | Yes | 192 kHz | $149 | ✓ | | Focusrite Scarlett 2i2 4th Gen | 8.5 ms | 11.7 ms | Yes | 192 kHz | $199 | ✓ | | Behringer UCA222 | 14.8 ms | 22.4 ms | No | 48 kHz | $39 | ✓ | | Behringer UMC22 | 11.9 ms | 16.2 ms | Yes | 48 kHz | $59 | ✓* | | MOTU M2 | 6.8 ms | 9.3 ms | Yes | 192 kHz | $229 | ✓ | | Audient EVO 4 | 7.9 ms | 10.8 ms | Yes | 96 kHz | $169 | ✓†|
*UMC22: use USB 2.0 port on Pi 5 †EVO 4: occasional 96 kHz negotiation issues; use 48 kHz with JACK
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Recommendations by Use Case
Cheapest option that’s actually usable for amp modeling: Behringer UMC22. The UCA222 is not usable for real-time amp modeling — the latency is too high. The UMC22’s 11.9 ms at 64 samples on Pi 5 is tight but workable for bedroom practice. If your budget forces you under $75 CAD, this is the one.
Lowest latency: MOTU M2. 6.8 ms RTL on Pi 5 at 64 samples is the best in this group by a meaningful margin. If you’re building a stage rig or you’re just latency-sensitive, the M2 is worth the $229.
Best DAC / best audio quality for monitoring and recording: MOTU M2 again, but the Audient EVO 4 is close and costs $60 less. If you’re mostly monitoring through headphones or studio monitors and want clean, accurate reproduction of your NAM captures, either will serve well. The M2 edges ahead on DAC measurements; the EVO 4 edges ahead on preamp neutrality.
Best all-rounder for a first serious rig: Focusrite Scarlett Solo 4th Gen. The driver compatibility is bulletproof, the latency is good (not best-in-class, but genuinely usable), phantom power is included, and the price is reasonable. If you’re setting up a Pi 5 rig following our original build guide, the Solo is the path of least resistance.
Best for streaming (OBS on a Pi, or audio out to a streaming PC): Focusrite Scarlett 2i2 4th Gen. The second output lets you send a processed feed to a capture card or secondary machine while monitoring locally. The Focusrite ASIO driver behaviour under Linux is also well-documented, which matters when you’re troubleshooting pipewire-jack routing at 1 AM.
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Final Thought
The Pi 5’s BCM2712 changed what’s actually possible here. RTL numbers that required a dedicated DSP unit two years ago are now achievable with off-the-shelf hardware and open-source software. But none of that matters if you’re trying to run NAM through a UCA222 at 128 samples — you’ll blame the software when the interface is the problem. Buy the interface that matches your actual use case, not the one that’s cheapest in the cart.
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