OK. I have tried 2 different USB audio interfaces with supposedly nice XLR preamps built-in. Yet I am still getting unacceptable levels of noise off them, and I’m wondering if this is normal, or if there is something else wrong with my setup?
Here’s what happens. I did a test. With no microphone or cable or anything plugged in, when I turn up the gain all the way (phantom power off), the Art gets about -62db noise, and the Alesis is even worse with about -52db noise.
I’m trying to use these things as preamps for my Live LoopingTests. Eventually I’d like to add more FX per track like Dub FX, but in preliminary tests, the FX chains just amplify the noise too much.
So my questions are I guess…
Are these things really that noisy or is there possibly something wrong with my setup?
Am I ever gonna get good performance out of a low end device like this?
Would a separate mic preamp help, because it would be adding gain to the signal and I wouldn’t have to gain the audio interface so much?
From my experience (which is only Firewire), it can happen that your computer power unit and / or logical board is not correctly shielded /interference-suppressed. If the audio device now can be powered either thru usb / firewire or with a separate power supply, you need to “isolate” (do not do this by hand!!) the power from firewire / usb first, to decouple the audio device from the computer. On firewire, you can do this by buying some 1$ firewire 6pins-to-4pins adapter and a 4-pins-to-6-pins adapter (and put these together), or use a cable with a 4-pin on one side (if your computer has a 4 pin connector, too). I don’t know if it’s possible to isolate the power source in a usb cable… At very first, just try with the audio power plug instead usb powered. EDIT: This also happens on “high quality” / expensive interfaces.
The second you can try is to isolate the ground of your power connector of the power plug of the audio device, if there is one. On german connectors you can do this by adding lot of sticky tape to it. Try the same with the computer power connector (but do not consider this as a permanent solution, ground connector existence has a reason). This approach helps 100% on my crap and expensive sony vaio notebook for the internal audio (isolating ground from power supply).
The third thing is a big new problem, which I have on my home in the city: Mobile providers (at least in Germany) currently heavily extending LTE mobile bands by adding huge transmitter over the city. These transmitters heavily disturb audio interfaces, speakers, microphones and guitars. If there is some kind of high frequency noise (different from random noise), it could be a LTE/mobile transmitter around. Put a lot of aluminium foil around your device and/or the speakers and see if something changes. Ah, of course around the mic, too ( most important) ! This seems to be especially a German problem, since the limit values are totally lax in Germany in comparison to other EU countries like Poland or even Russia (factor 10 to 100 higher). Pro industry against citizens, as always.
The list of issues, could be large, but you could narrow it down by trying it with another computer. I don’t think this sounds like the noise you’d get from usb powering issues. and I wouldn’t think that a proper interface would even care about those (unless you have serious issues with the computer/powerusply/grid) and is filtering it all anyway.
As far as I know you can apply the 5vdc from other sources as well.
0xrns, kind of what I was afraid of. I’m going to test my signal to noise ratio on both interfaces and just stick with whichever one I get a better signal out of.
After a little testing, it seems the Alesis gets better gain and therefore less noise…
With roughly the same “check check” level, when both amps are turned roughly 3/4ths the way up, there is about -70db of noise even with no microphone connected.
With multiple “check check” tests with my XLR Headset mic positioned at the same distance from my mouth, I got about -19db with the Alesis, and only about -30db with the Art
So basically I’ve got about 50db dynamic range with the Alesis, or something like that.
I guess it would be acceptable for recording stuff, but I’m still concerned about how much noise will be added by the FX chains for live looping stuff.