Hi all.
Great forum. Really impressed with the detailed info on it.
I picked up a new UMC204HD yesterday. Testing it today (to see at what level it clips) I notice that its audio outputs look VERY noisy. It’s all high frequency noise (except for a small amount of hiss, very little of it’s in the audio bandwidth). But it still seems very high and I’m wondering if this is normal for this unit - or if mine’s faulty.
Fernand (page 15 of this thread) mentions a similar thing.
My scope is measuring the noise at around 90mv rms (see pic). You can see the noise clearly superimposed on a 1vrm sinewave (see pic). For control the second channel is muted.
- I calculate the noise at -21db!!! (1vrms/89mvrms) (left channel 1k sinewave/right channel no signal)
- The noise comes out of all four rca outputs.
- And both TRS outputs.
- The TRS outputs are unbalanced (sleeve is grounded) so you can’t use a balanced output to avoid it.
- The noise is out of phase on different channels (so seems unlikely to be internal psu noise)
- My analogue scope shows exactly the same noise at the same level as the digital one.
- In comparison my crappy old usb soundblaster SB0490 is whisper quiet.
- You get the same noise on different laptops, win10 (I even installed the drivers) and linux
- You even get the same noise just powering the thing up on a usb charger (no laptop)
- So its the soundcard itself that is generating this noise and not any apps controlling it.
As I said its mostly high frequency. I ran it via a digital mixer (effectively a 20hz low pass filter) and it cleaned up a lot. So apart from some faint residual hiss it’s not audible. I was able to measure 85db signal-to-noise on the graphs on the mixer (probably the limits of its performance).
However even though I can’t hear it, and my speakers can’t play it - I guess a lot of this high frequency crud will be getting into my amp and heating it up. So it doesn’t seem right to me.
Does anyone have any thoughts on this.
Thanks in advance
Sieskid
(australia)