Issues with Emu tracker and THD measurements

[Salas]

Will do that too, but your Emu PC card has to have an edge over the USB box with its various bells and whistles even if they are family.

[Salas]

Originally posted by syn08


You have most likely a problem with the PatchMix. Use the default profile and mute down anything not absolutely required.

Did the muting, gained 1.5dB better noise floor, THD the same. This is fantastic performance for my standards. I am chuffed. Maybe it can do better with a faster 64bit PC with lots of fast mem. It also does well for noise floor up high to 96kHz when sampling at 192k.

Thanks all you guys for your expertise!

[fotios]

The PC used is: Intel C2D-3GHz (E6850), 8GB DDR2 sync, FSB 1332MHz. The OS is WinXP x64.
EMU is connected in loopback mode via two balanced cables from out to in. The results presented are not the better. I have obtained better results when the EMU is a little warmed. After half an hour, those are worse. This caused from the analog ICs used in inputs and outputs, as well the volume pots... by no way i can obtain the results of the PCI EMU of Syn88. This because i have installed only the drivers of EMU and its software mixer sliders (only 3) are in max place, so i can adjust volume only from the physical pots of EMU which is a bit difficult. Also, if you are patient and have a good PC, by selecting 1,048 millions FFT samples, then there is an improvement in results.
Anyway, see the results in the picture

[Salas]

Still my loop is single ended so I may expect a bit more with balanced?
Its a 15cm loop non the less.

[Stefanoo]

Originally posted by syn08


You have most likely a problem with the PatchMix. Use the default profile and mute down anything not absolutely required.

mmm.....what do i need to mute?
Looking at spectraplus' s website they ran tests and put them on the web on EMU tracker pre.
They get as somebody else THD 0.00045% and SNR 107dB.

mmmm.....might there be some problems with my soundcard?
But then i see salas that got the very same result...so.....

might it be something on the set up?
I ran it Single end.
Maybe they used balanced mode (it's not specified)

link

http://www.spectraplus.com/Downloads...t%20report.pdf

[Stefanoo]

Originally posted by salas
0.00041% and -150dB noise floor from 300Hz to 24kHz with the USB one at -15dB like your level. That's the best I will ever get with tracker pre, and its super for my needs. Buttons and USB cable give the edge to your PC card. Thanks Syn08.

what settings did you use to obtain 0.00041%?
what did you mute?

[syn08]

Originally posted by salas
Still my loop is single ended so I may expect a bit more with balanced?
Its a 15cm loop non the less.

Welcome to the real world!

You just got another good reason why I will never use a sound card for sensitive measurements. True, my place is known as horrible when it comes to noise, in particular mains frequency, so you may do a little better.

Here's the wonderful EMU you just praised, in single ended mode, loop is 6ft. (certainly required to do measurements on the bench). Note that I can do, in the same place, with my pro analyzers, and the same loop length, only -140dB noise floor single ended (1601 points, so much more RBW though) but absolutely no residuals.

The last reason for not using sound cards for measurements is the AC coupling only. I care about PSD and noise well under 20Hz. I also care about low frequency distortions, not possible to reliable and precise measure. These cards are full of low end/cheap electrolytics.

Edit: Wrong picture, level was not compensated for the single ended loss. It's ok now.

[fotios]

Originally posted by salas
Still my loop is single ended so I may expect a bit more with balanced?
Its a 15cm loop non the less.

I think this is not the issue... i mean the length of cables. As you probably know, balanced outputs formed from an inverting IC which follows a non-inverting IC. From these two ICs we get the Balnced signal (hot - cold). Balanced inputs formed from a subtracter IC which in the best case it is buffered from inputs via two voltage followers IC. Subtracter as you know, converts the balanced signal to single ended. If we use mono Jack plugs, then in output the inverter IC output is grounded. In input, the - input is also grounded. Although we are used to do this in our work (between efx or eq units) because is there not any audible effectwe ignore it for small length cables. But... maybe in this measurement system this plays some role. I used from the begining balanced cables, and i can't inform you for the effect (if exists) of using unbalanced cables. Do an experiment, it is simple.
I will also mute the unused inputs in windows mixer. The meas shown in my picture was taken with all inputs unmuted. I will inform you if there are better results.

Fotios

[fotios]

Yes, the mutting of unused inputs was some effective. In the right channel i got:
THD arround 0,00020%
THD+Noise arround 0,00021%
SNR arround 114 dB.
These values obtained, are very close to PCI EMU of Syn88 presented in his first post.
I think can be better because the little instabillity presented by the EMU usb. Looking the spectrogram running, i observe allways the three parameters to get gradually better values untill some moment, and after it again gradually to get worse values. But, for example, THD never exceeds 0,00050%.

Fotios

[Stefanoo]

i still don't understand: what did you exactly mute? and where did you mute those things? through the mixer?

mmmm....i can't reach that low THD, what setting did you use on spetra for the specific case of THD 0.00020?


I did notice that numbers go down till a certian point where all of a suddent they go up....maybe it is due to the fact that the PC is elaborating some other datas for Win...i don't know!