USB interfaces; a general note

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    Ted Fletcher

    I have been using various USB interfaces since the days they were invented and recently I needed to research what’s ‘state of the art’ and what’s available to link monitors, microphones, record and playback. I was amazed at the variety of little boxes that are suddenly available, and then on closer inspection, I noticed how similar they all are and how the flowery descriptions don’t say very much except to claim some level of superiority.
    Clearly, all the ones I have seen are made in China and all seem to have identical functions with some slightly dodgy claims.
    I decided to try some critical tests on a few of them and the results are interesting.
    For the past couple of years I have been using an inexpensive ‘SubZero SZ-A12’ interface which seemed to work well and has excellent performance.
    It is capable of 24 bit 96KHz operation and it has excellent power supply noise suppression. The audio performance is good enough for most of my research work; response within 0.1dB across the selected range, harmonic distortion mostly down in the noise which is well down near the -100dB mark.
    Some of the new ones available are claiming 24 bit 192KHz so I bought a couple and hit them with the same tests……. Oh dear!
    Amplitude frequency response is generally OK, well it should be. The newer interface chips do have marginally improved noise levels, however the harmonic distortions are far from satisfactory, there is significant 3rd order distortion (around 0.1% at operating level) and it is much higher than the less obtrusive 2nd order distortion. But the worst performance is with crosstalk, L/R crostalk at 1KHz was very bad at about 40dB down. Checking frequencies up towards the upper limit of 20KHz the crosstalk gets to just a few dB! I can only assume that the layout engineers learn about digits but not about audio!
    I shall stick to my SubZero SZ-A12 unit; looking at some newer equipment proves the old saying ‘improvement means deterioration’!


    Thanks for sharing your insights on USB interfaces. It’s always interesting to hear about your experiences and your critical tests. It’s true that there is a wide variety of options out there, and sometimes it can be difficult to navigate through all the marketing claims and find a truly reliable and high-performing device.

    I’ve been using RME interfaces for maybe ten years now, they are bullet proof and sound great. The other good brands are UAD, Apogee, and then Focusrite make affordable options.

    It’s great to hear that the SubZero SZ-A12 has been working well for you and meeting your needs. It’s always reassuring when you find a piece of gear that performs reliably and consistently. The fact that it has good power supply noise suppression and excellent audio performance is definitely a plus.

    I can understand your disappointment with some of the newer interfaces claiming higher sample rates. It’s unfortunate that they didn’t meet your expectations in terms of harmonic distortion and crosstalk. It’s important to remember that higher sample rates alone don’t guarantee better audio quality. The design and implementation of the interface play a crucial role in achieving optimal performance.

    It’s also worth considering that different interfaces may have different target markets and price points, which can affect their overall performance and quality. Sometimes, inexpensive options like the SubZero SZ-A12 can surprise us with their capabilities.

    At the end of the day, finding the right gear is about balancing your needs, budget, and performance expectations. It’s great that you’ve found a reliable interface that meets your needs, and I’m sure it will continue to serve you well.

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