Howto - Distortion Measurements with REW

I don't have a Focusrite, but I'd try another ASIO driver, e.g. ASIO4ALL or other although I'd expect the Focusrite driver to be a good ASIO implementation.

For Win, some people reported they also need to disable the other non-soundcard interfaces in their settings, e.g. in my case, the internal Realtek in my laptop.
 

LKA

Member
2014-12-28 5:31 pm
As I see my old modified usb card SB1240 is better than many newer ones.
 

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This is an external USB card, X-Fi USB HD (SB1240)

1st improvement
2nd improvement
I replaced 5 opamps
Thanks for sharing your mods. That was quite a bit of work! Having a $99 sound interface that is almost that good is fine for me. I wonder if opamp upgrades inside my 2i4 will improve performance?
 
I'd say check it with a loopback connection or re-check the loopback connection. Also try maxing out the Buffer samples in the ASIO Control Panel. Third thing you can check is your Volume Mixer in Win, then re-check levels in R.E.W.

Without R.E.W., does the audio interface both play back audio and record audio?

I just checked for interference with mains by putting the UMC202HD on top of a DC PSU, and sure enough, bumps at 60, 180, 300Hz.

Tested self-noise measurements with Browser open several tabs + Wi-Fi, then Browser closed + Wi-Fi, then Browser closed and Wi-Fi Off. Measurements seem close to me.
 

YashN

Member
2013-12-04 12:55 am
Canada
To check whether measurements with a smaller frequency range can provide less THD in calculations because my card has some spurious high-freq spikes, I did two measurements: first is 20-20kHz in the measurements window, and second is 10-48kHz. Both are with the card set at 96kHz using the ASIO driver. The respective measurements are below.

Does anyone know why I don't get any calculated figures in the Distortion window for the smaller range of frequencies?

Dist20-20k.jpg


You can see above that the table below the graph, with the Fundamental, Harmonics and THD has no numbers at all.

Now here is the larger frequency range:

Dist10-48k.jpg


Here, we do see the measured and calculated numbers for each entry.

Do you sometimes get these missing numbers? Is it user error?