Sorry but English is not my strong point ... someone kindly explains to me what this wording in the manual means?
Quarter-inch line outputs are not cross-coupled. Therefore, when connecting them to an unbalanced input, use a TRS plug with the ring disconnected. Not floating the negative terminal will short it to the sleeve ground and cause distortion.
Which is the ring to be disconnected?
Hello everyone, I know this is old topic, but I did not see anyone publishing measurements.
So I followed the
Rane paper to create my own cable (TRS with Ring not connected) and compared it to a standard TS cable. Motu says only the output will be impacted, and I can confirm that. So let's see if distorsion increases.
For the sake of clarity, I'll refer to TRS with Ring disconnected as "TRS(d)" in the rest of this message. So if I mention TRS, it means standard connector with Tip, Ring and Sleeve connected.
I did this test in loopback - TRS(d) out to TS in, TS out to TRS(d) in. I did the same with TS out / TS in as well. That TS out / TS in shows exact same results (performance degradation - see below) as with TS out / TRS(d) in, which demonstrates that the output is influenced by TS vs TRS(d) connectors, as per Motu's documentation.
I also repeated the same test, inserting a high definition analog device in the loop (a preamplifier, not to mention it). So in that case, the connections where TRS(d) to RCA -> RCA to TS, or TS to RCA -> RCA to TRS(d). The findings are the same with or without the preamplifier in the loop.
Enough blabla, there you go with the results (and I'm sorry, in that print screen TRS means TRS(d)):
This is a THD vs Level measurement with linear scale (because I prefer
), in dBr unweighted.
I removed frequencies below 200Hz as differences are nor relevant and also because I had too many FFT windowing errors screwing up the sweep, and I got bored trying to have a clean one at that resolution (6 points per octave). As you can see, yes there are differences but they are negligible.
I did a second sweep with lower resolution (2 PPO) and now you have the view from 20Hz. And this time it's log scale
Last note, find below a single FFT (1kHz) that shows a little more, even if these differences do not impact the THD since they are very low level noise. The green trace below (TS out) shows some spikes not present with TRS(d) out (which is the pink trace):
I would recommend to follow Motu's instruction but I must admit it's unlikely to make a sonic difference.
Enjoy your Motu!