Technical comparison of sound cards: Presonus AudioBox USB/FocusRite Scarlett 2i2

At ExpORL we've standardised on RME sound cards (in particular the Hammerfall DSP Multiface II and Fireface UC) for all our behavioural and objective experiments. While these perform very well, they're also very expensive. We therefore explored whether two much cheaper sound cards, the Presonus AudioBox USB and FocusRite Scarlett 2i2, would be suitable for certain experiments with less strict requirements, such as speech intelligibility in noise.

We concluded that the Presonus AudioBox USB is not suitable for faithful playback nor recording because there is too much stereo crosstalk. The FocusRite Scarlett 2i2 is suitable for faithful playback or recording of audio. However, one has to be aware of the following constraints:

• Its output dynamic range (around 96 dB) might might be to small for e.g. tone audiometry for hearing impaired people.
• The sound card is not suitable for playback and recording simultaneously, since the inputs are directly routed to the main output, even if direct monitoring is switched off (for which there is a hardware switch)
• Input and output gains are adapted with analog hardware knobs (as opposed to the RME sound cards that are set within the driver software). We advise to set the monitor level at the maximum for optimal performance and to avoid ambiguous calibration; input gains should be adjusted such that no clipping occurs.

We analyzed the sound cards using RightMark Audio Analyzer (RMAA) and used the RME Fireface UC as a reference. We used stereo sound cables to obtain balanced input/output. For each test, we used 44 kHz, 32-bit (float) audio. Our test results can be found below.

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Complete sound card tests (input coupled to output)

Summary

Test	AudioBox USB Audio	Focusrite Scarlett 2i2 USB	RME Fireface UC
Frequency response (from 40 Hz to 15 kHz), dB:	-0.20, -0.52	-0.01, -0.07	+0.03, -0.03
Noise level, dB (A):	-94.4	-95.8	-109.9
Dynamic range, dB (A):	94.8	95.6	109.9
THD, %:	0.0048	0.0009	0.0016
IMD + Noise, %:	3.776	0.0071	0.0019
Stereo crosstalk, dB:	-42.9	-95.5	-109.5

Frequency response

Noise level

Dynamic range

THD + Noise (at -3 dB FS)

Intermodulation distortion

Stereo crosstalk

Inputs only (output of RME)

Summary

Test	AudioBox USB Audio	Focusrite Scarlett 2i2 USB
Frequency response (from 40 Hz to 15 kHz), dB:	+0.04, -0.17	+0.05, -0.33
Noise level, dB (A):	-98.6	-98.2
Dynamic range, dB (A):	100.4	98.1
THD, %:	0.0031	0.0018
IMD + Noise, %:	0.027	0.0042
Stereo crosstalk, dB:	-99.3	-98.6

Frequency response

Noise level

Dynamic range

THD + Noise (at -3 dB FS)

Intermodulation distortion

Stereo crosstalk

Outputs only (input of RME)

Summary

Test	AudioBox USB Audio	Scarlett 2i2 USB
Frequency response (from 40 Hz to 15 kHz), dB:	+0.06, -0.22	+0.01, -0.08
Noise level, dB (A):	-96.9	-96.9
Dynamic range, dB (A):	96.7	96.6
THD, %:	0.0047	0.0011
IMD + Noise, %:	0.012	0.0044
Stereo crosstalk, dB:	-95.6	-89.7

Frequency response

Noise level

Dynamic range

THD + Noise (at -3 dB FS)

Intermodulation distortion

Stereo crosstalk

We could not eliminate low frequency crosstalk for Presonus AudioBox USB. High frequency crosstalk disappeared for the FocusRite Scarlett 2i2 with the MONITOR-knob turned at its maximum: