Which USB Interface for Device Measurements?

[Mikey Antonakakis]

I am working on restoring a vintage receiver/integrated amp, and I currently have an M-Track Solo that I’ve been using to take measurements. I am hoping to upgrade to something nicer, maybe around the $200 price point, to continue making measurements for occasional hobby work on amps and whatnot, as well as for daily use/listening with a dual computer setup (work laptop with dock and gaming PC, currently using a USB switch for convenient switching between which one I use).

Ideally when using the interface for taking measurements of devices, I would like to use my desktop, but since it is somewhat built to “gaming” specs I think there might be some issues with noise over USB power/ground. With the M-Track Solo, I can hear all sorts of stuff on my house’s mains, even on different breakers, like the sparks of my gas boiler starting up. And static discharge (thanks low-humidity Colorado), for instance walking into the carpeted office in socks and habitually discharging myself on the painted metal legs of my desk - “pop” from the speakers even though my desk legs do not have any low-impedance connections to anything. It does this with different amps/powered speakers connected to the M-Track, although I haven’t conclusively ruled out that it might be the amps themselves (so far Klipsch ProMedia 2.1, Marantz 2220B, and some older Yamaha desktop 2.1 combo). Needless to say this sensitivity to external factors is making it tough for me to trust the repeatability of my measurements. Maybe it’s not the fault of the M-Track, but I’d like to upgrade regardless and want to choose an interface that might help improve any potential noise on the USB from leaking into the DAC.

I actually tried to buy a Focusrite 2i2 today, but didn’t realize until I was halfway home from Guitar Center that they sold me a Solo instead (that explains the low price! Had my toddler with me who just started walking and wanted to explore a decidedly not-toddler-friendly store so I was a little distracted at checkout ha). I was also considering the MOTU M2, and looking for any other suggestions for a “mostly listening, sometimes measuring” USB interface. Any tips to decrease noise regardless of hardware would also be much appreciated!

(Note: I mentioned this in my first thread on the forums recently but I think it probably got lost in there).

 

[somebodyelse]

Most of what you describe could probably be avoided with a USB isolator if you can't use balanced connections - see for example https://archimago.blogspot.com/2021/09/measurements-usb-isolation-with.html for some measurements and discussion of isolators, single ended vs. balanced. There are several more idolator articles at the same site, and a few here. The cheap isolators so far have limited USB speed which is ok for stereo at ordinary sample rates but not for high sample rates or channel counts. Updated chipsets from AD and TI exist but haven't made it to the lower end of the market yet (unless I missed them!) so if you need higher speeds you probably need more expensive isolators like the Intona ones. Check the speed specs carefully as it's easy to miss. I'd address this before changing interface as it may affect any of them.

On the measurement front have a look at the E1DA Cosmos ADC and APU, whatever QuantAsylum are currently producing, and the LinearAudio Autoranger. You should be able to find somethreads here and at archimago's blog about them. Cosmos gives great measurement capability if you know what you're doing. The others are more user friendly but a little less capable.

 

[SSS]

For measurements I use E-MU Tracker USB recording box. It is old and bought used. Works fine up to 90 kHz. Tried an USB isolater which created some peaks in the FFT display. Maybe there are better ones out there? Not to get hum or similar problem I use my DUT (device under test) isolated with a mains transformer. Software is audiotester (Germany) and ARTA. Use sometimes also REW.

 

[Mikey Antonakakis]

Took the Focusrite Solo back and got an open-box 2i2. Was also considering a Universal Audio Volt 2 since it is not powered from USB, but going to give 2i2 a shot first.

On the Marantz I am working on, hooking it up with a TS-RCA cable with no signal coming out of the 2i2 results in a fun party trick: if I crank the volume on the receiver, I can hear an AM radio station getting picked up by the cable haha (is not affected at all by 2i2 output level or tuner setting on the receiver). The M-Track Solo with its RCA output does not exhibit the same issue. Certainly won’t help with my measurement accuracy!

Going to convert the TS-RCA cable to TRS-RCA per the RANE recommendations (10b) to see if that help. Single-conductor shielded cable with TRS tip to RCA center pin and TRS sleeve to RCA sleeve. TRS ring disconnected.