USB sound card for audio spectrum analysis

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#182
SY said:
Hp, did you measure third harmonic of the 10k? Thanks.
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Well, you may know, may you read on the later "Low-distortion Audio-range Oscillator"... topic..

The real THD of the LDO is usual lower as the LNA &ADC shows up! This means, a direct measurement, as FFT does, will show you a Brut Force measurement with the underlying LNA & ADC performance! Also will show you the phase noise around the fundamental signal.

In other words, the THD3 or THDxx may show -120dB and really is may on -140dB. To get into this real THD, a additional filtering of the Har1 is needed / required. Look at the later Samuel Groner's "Low-distortion Audio-range Oscillator" measurement.

Hp
 
#184
 
#186
mkc said:
Hi Victor,

Thank you. You have removed the potentiometer from the left channel also. Have you done this to make fixed gain?

Mogens
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Yes, potentiometers was also removed. Previously, I done similar job for both channels, but later, when I can't get good results from the left channel, I blocked it. Gain is fixed. I already have the external divider for the level changes.

Regards,
Victor.
 
#188
Impressive, below -130db.
are you use your your low noise 1khz oscillator for feeding the signal to E-MU0202?

vicnic said:
Wish to tell you little about one amazing result with the E-MU 0202. Not far ago got this card from the ebay auction for . I was planning this for my laptop as spectrum measurement tool. This USB sound card uses AK5385 as ADC. The chip is semi compatible with the AK5394, and I thought, that maybe I can replace the ADC chip, if it needed, but seems that is not needed. After one working day, some changes in the buffer amp and little tricks I got wonderful results from the right channel of the ADC. The left channel was more worse (seems that the chip internal problems), and I blocked it. As result I got this relatively small "magic" box, and the nice spectrum picture:
http://content32-foto.inbox.lv/albums/v/viccc/E-MU-0202/0202out.jpg
http://content32-foto.inbox.lv/albums/v/viccc/E-MU-0202/1kHz0202.jpg
http://content32-foto.inbox.lv/albums/v/viccc/E-MU-0202/0202ins.jpg

Victor.
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#196
I have tried a couple of USB sound cards, to meet my need for manufacturing test and general engineering until I can afford a AP.... Looking for THD min -100 dB and with digital I/O.

Used to use an EMU-0404 together with ARTA under Windows XP, but after upgrading to Windows 7 it just didn't work anymore, even after installing their beta Windows 7 drivers.... When it worked I was happy with it, although 192 Khz didn't work with ARTA. Fine hardware, with both Toslink and RCA digital I/O, but drivers suck.

For production testing I got a low cost Steinberg UR22. Software is fine, but hardware limited, no digital I/O and analog output only unbalanced. Loopback 1 Khz THD @ -1 dB (referenced to 1.4V RMS) is -81 dB, not something to write home about, but just about good enough for dam1021 production testing. Mine was a mkI, had the low frequency noise problem. MkII might be better, but didn't bother....

Then I got a Roland UA-55. At first it looked ok, balanced I/O and with RCA digital I/O, software is fine. Loopback 1 Khz THD @ -1 dB is -84 dB, better but not much. Then I found out that THD went skyhigh when running with unbalanced input, so it got thrown aside.

Finally I got a Focusrite 6i6 2nd gen, the most expensive of them, but still reasonable. Hardware is very good, balanced analog I/O and RCA digital I/O, software is fine, but user interface confusing. Loopback 1 Khz THD @ -1 db is good at -96 db, falling to excellent -105 db at -10 db level. THD increases at higher frequencies, and it have the usual high frequency modulator noise. For now it's a keeper, might get more for production testing.
 
#199
This one can do -110dB THD and -101dB THD+N @-3dBFS, not bad for a card that costs EUR35-60 from eBay (I just ordered one 🙂).

It even has Toslink for digital in/out, the catch being that it only works with Windows XP/7 and needs FireWire.
 

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