A Winner, after all!
Using the EMU 0202 USB with PRAXIS, for 96kHz (or even 192kHz) sampling
There has been one of these EMU 0202 USB2.0 soundcards knocking around here for several months now. The possibility of finding a good laptop-compatible 96kHz or 192kHz card for under $120 (current price at Amazon) was too tempting so we bought one to try. But first experience with the EMU 0202 wasn't encouraging, so there wasn't a lot of enthusiasm for detailed tests when there were other demands on time..
Before we get into why the EMU 0202 actually is a good choice after all, let me list its negatives, both actual and those only suspected:
It uses two 1/4 inch phone jacks for the inputs. And the two channels use different types of phone jacks (the right channel jack is a combo XLR/phone type). Which brought up worries about how well the circuitry inside actually matches for the two channels. (no evidence of a problem with this was found, though)
It won't work under Windows 2000 and as of this moment (July 13, 2007) does not have any VISTA drivers. So for now, its good for XP only.
It has mechanical input level knobs. These are usually a problem, since it's not usually practical to keep knobs always set to a precise spot to preserve calibration -- unless they can be used at an extreme setting, which will be repeatable
First tests (trying to use the XP drivers in VISTA) showed irregular operation at 96kHz and 192kHz.
EMU's parent company is Creative Labs, which has always seemed to find a way of putting some kind of snag (if not a fatal problem) into use of its products with PRAXIS.
After putting it off for so long, I finally spent several hours today working with the EMU 0202. To get around the 1/4 inch jack problem, I got some mono 1/4 inch phone -to- RCA jack adaptors -- cheap and easy to come by at Radio Shack or from Parts Express or other places that sell audio adaptors. Then, into the RCA jacks, I plugged a stereo RCA plug -to- 3.5mm stereo mini-phone plug cable. The 3.5mm plug was for the AudPod's "to Soundcard input" jack, of course.
Connecting from the 0202's line output was easy, since it is provided on a 3.5mm stereo mini-phone jack (along with two 1/4 inch jacks that I didn't use). So just a stereo 3.5mm plug to plug cable (like those supplied with PRAXIS) was all that was needed to connect to the AudPod's "From soundcard output jack".
The new tests were done on a 1.7GHz Celeron machine running Windows XP. Installation of the 0202's driver was nicely simple. And unlike with many of Creative's cards, the installation didn't try to put huge amounts of throwaway programs and dumb features and useless shortcuts all over the Windows desktop. Thank you, EMU.
But first attempts to calibrate the card in PRAXIS failed. The line inputs on the 0202 have just an insane amount of gain when the input level knobs are set all the way up -- it just wouldn't work, the whole setup was unstable and noisy. I set the knobs about midway and the device then calibrated normally, but that's not really acceptable -- one bump of a knob and calibration would be forever lost. I did make some acquisitions that way and found that the unit would work at high sample rates. And the sampling is NOT automatically rate converted from a single actual sample rate, which is good news and avoids a common complaint about Creative labs soundcards (with which 44.1kHz operation is usually abysmal)..
I was about to write the 0202 off, when it occurred to me to try with the input level knobs set to minimum. Analog type level knobs will normally let NO signal through when set all the way to the left. But not on the EMU 0202 -- minimum gain (full counterclockwise) is actually a moderate setting with very low noise. I calibrated with that and not only did I have a setup with easily repeatable input gain, but the input noise was quite a bit lower.
One warning about sample rates, though: the 0202 will natively use whatever sample rate it is set to (when set via the EMU USB Control Panel applet), and XP will just try to rate convert that to whatever PRAXIS asks for. If you set that to 192kHz, it can still work at 48kHz, but it wastes a lot of bandwidth and runs higher risk of the machine not keeping up with things. So, at least when doing the PRAXIS calibration, set the EMU USB Control Panel for 48kHz. You should set it to higher rates, later, if you will be working at higher sample rates. For best result, set the EMU control panel sample rate and the PRAXIS sample rate to the same setting.
Like most pro-level cards, it has no Windows Input Mixer (or rather, it has one, but there are no controls on it). So during the first part of the Praxis calibration, set the knobs on the unit fully counterclockwise and ignore instructions about setting the input mixer selections and levels.
Below are shown some plots taken of the EMU 0202 doing dual channel FFTs while outputting seven sine tones on each output channel.
Above is the unit operating at 24bits/192kHz, looped back through the AudPod. The noise floor rises quite a bit above 40kHz, which may limit reasons to use it at the 192kHz rate. Also, it is easier to disturb the acquisition at 192kHz, so unless you REALLY need 192kHz sampling for a given test, I suggest staying with 48kHz or 96kHz.
Above is a real surprise. This one is looping from the EMU output to its input with just cables (no AudPod in the loop). The EMU 0202 is considerably quieter than the AudPod! Also, the distortion measured without the AudPod was quite a bit lower (I even saw it down to 0.0003% THD at midband, which is insanely low). This is the first card in which I've seen a substantial improvement when going from 16bits to 24bits. When using this in PRAXIS measurements, the AudPod device becomes the limiting factor for both noise and distortion. That doesn't happen often. I'd bet this would be a great recording card.
Here is another take, done at 24bits/96kHz (the output level was a few dB hotter, which probably explains the distortion products starting to appear at around 20kHz):
You can see the noise starting to rise at the same place as with 192kHz sampling, but it doesn't bother the dynamic range much, here in the lower bandwidth. So, I'd say its a great 24/96kHz card and a not-as-great one at 192kHz. Of course considering how few USB cards even do 96kHz decently, that's quite an accomplishment.
Here's a summary of how to use the EMU 0202 USB with PRAXIS:
Make sure you are running Windows XP (at least for now)
Liberty Instruments does NOT sell any EMU cards -- if you want one, do a Google search on the internet or go to Amazon.com.
Get some adaptors and adaptor cables as described above, using the two 1/4" phone inputs to the EMU 0202 USB and its single stereo 3.5mm output.
Calibrate and run the 0202 USB with its input gain controls set to FULL COUNTERCLOCKWISE
There's no Windows mixer for input, so during calibration, just run through the stuff about messing with the Input (or Record) mixer.
Of course, keep the "Direct Monitor" function OFF!
Calibrate with the EMU Mixer selected for 48kHz. For use at higher sample rates, remember to change the EMU's sample rate to match.
The usual suggestions for USB cards still hold: minimize lengths of USB and audio cables between computer, AudPod and the soundcard.
I didn't mention it above, but I got lowest noise with the EMU's "Ground lift" switches (on the bottom of the box) set toward the right.
Don't use a sample rate higher than you need for a measurement. Avoid 192kHz unless you actually need to measure something up there. For microphone-based measurements, forget about using 192kHz, there aren't many flat to that high.