MobilePre USB review

When USB audio interfaces first appeared, there were numerous problems getting them to work effectively, but competition is now fierce, particularly in the semi-pro recording market. These two units from M-Audio are primarily aimed at mobile recording, but are equally at home in the project studio. The Audiophile USB requires a chunky 305g power adaptor to add to the 584g weight, but the MobilePre USB is entirely USB powered, further enhancing its portable appeal - it weighs in at just 574g.

Both units were tested with a 900MHz Pentium-M Toshiba R100 and Emagic's Logic Audio 5.5, recording and playing back live vocals, electro-acoustic guitar, sound modules and commercially recorded CDs.

The Audiophile USB has a 24-bit, 96kHz interface offering 1/4in line-level inputs, RCA phono and coaxial S/PDIF-in and -out as well as MIDI-in and -out. It can only handle one stereo 24-bit, 96kHz input at a time, although all four (both analog and digital I/O) will work at up to 16-bit, 48kHz as well as 44.1kHz.

That isn't as restrictive as it initially seems, as you'll only need 24-bit, 96kHz transfers in exceptional circumstances. While the compatibility is useful for playing pre-recorded 24/96 sessions or DVD-Audio, the unbalanced inputs will put off those who would actually need this kind of resolution for recording.

Even so, with vocals recorded through a quality valve mic preamp, the combined noise of eight heavily compressed tracks was impressively low, and the playback of pre-recorded CDs was good too, with an even, clean sound. The overall impression was of a neutral response, confirmed by the perfectly usable recordings of the electro-acoustic guitar. Many low-cost units try to disguise the sound with digital signal processing, but the Audiophile's relative transparency is a far more usable approach.

The control panel software doesn't offer input-level metering or mixing, which would make life easier, but it's otherwise intuitive. It features access to latency settings, which are defined in five stages from 'Very Low' to 'Very High'. No figures are given in the driver, but the 'Medium' setting on our test system was certainly over the 20ms or so that will affect live performance and wouldn't go any lower without instability.

The Audiophile also sports a DD/DTS passthrough option to allow multichannel audio through the S/PDIF port for surround use - a nice touch. Other S/PDIF transfers are in consumer format and performed well with no discernable errors. MIDI timing proved to be rock solid too, even on the most demanding material, although the lack of an activity indicator is annoying.

For testing the MobilePre, we plugged an Audio-Technica AT4033a capacitor microphone directly into one of its unbalanced XLR channels. The lack of a software VU meter again made setting an appropriate gain level tricky and, with just signal/clip LEDs on the unit, inputs have to run quite low to be sure of avoiding unpleasant digital distortion. The test system managed the low-latency setting before causing audible artefacts, but this was still around 25-30ms and, while there's an option to directly monitor live inputs, software instruments will still suffer.

Listening back, the solid-state circuitry doesn't have the warmth of valve-based gear, but the sound is less thin and brittle than we expected. In comparison to higher-end units, vocals lacked a little presence in the upper mid-range and guitar was a touch muddy, but performance was nevertheless impressive given the MobilePre's price. The noise floor was again surprisingly low considering the unbalanced connection.