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Old 20th October 2013, 12:11 AM   #1
jayadev is offline jayadev  India
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Default RTA measurements and soundcard

This could be my baby steps for measuring stuffs I build.

Just bought a creative USB sound card.

presently I am on Toshiba laptop with i5 processor and 6gb Ram

Please notice the Graph from RTA.

Why is it slanted,I mean why is the frequency response not flat?Last snap is of onboard sound card which connexant HD and it is no different either.

Surprisingly Why do I see different readings from both the apps ? one is around TRTA85db while other REW is 110db. I am trying with demo spectra plus as well which looks much better.
Meanwhile the inputs are mute.


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File Type: jpg rta room.jpg (143.9 KB, 424 views)
File Type: jpg RTA2.JPG (132.1 KB, 391 views)
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Old 20th October 2013, 12:18 AM   #2
SY is offline SY  United States
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These are spectra of residual noise?

Remember, if you have a constant noise voltage density, the noise per octave increases by 6dB/octave with increasing frequency. Also, one is dBFS and the other is dBU.
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Old 20th October 2013, 01:41 AM   #3
jayadev is offline jayadev  India
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Hi Sy,
How do I make it flat to measure a preamplifier ?

Also the specs shows that SNR of the said sound card is 100db minimum.how far it could be true?

Any suggestions for a reliable straightforward measurement PC analysers ?

Is selecting DBfs proper ? the vertical dbu scale in Rew confused me.
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Last edited by jayadev; 20th October 2013 at 01:45 AM.
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Old 25th October 2013, 11:45 AM   #4
Eldam is offline Eldam  France
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Hi,

Funny, same problem to me, i sucess to have my first spectrum analys :

behringer ECM-8000 (non calibrate)
ARTA (free one)
E-MU Pre tracker Pro USB soundcard with Phantom alim to 48v from USB port (class A pre)

The Pink-noise .wav is send from my digital source with a reccording from Audiocheck.net.

Well, without noise in the room the curve is like a : W
I don't waiting for flat in the bass cause the room, but after 1000 hz with the micro in front of the speaker (50 cm), I would waiting for a flater curve without sound ! So after sending pink noise and freeze the curve... how to read a false curve !

Calibration ? Function in ARTA to flatthe curve before measure ?

Jayadev, the first who finds call the other
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Old 25th October 2013, 12:11 PM   #5
SY is offline SY  United States
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I'll try to remember to compose a decent reply later today when I'm not rushed.
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Old 25th October 2013, 12:30 PM   #6
Eldam is offline Eldam  France
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Hi Sy,

Don't ! Not yet please ... we have Jayadev and I to dig a little to find by ourselves... After all two days ago i was looking for how to take a measure and just suceess yesterday !

If in one week i don't find after reading the ressources here and elswhere, i will send a big Heeeeeeeeeeelp !

Have a nice day Sy,
eldam
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Old 25th October 2013, 01:10 PM   #7
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What bothers you guys is the non linearity of the spectrum. What surprises me is that with the mic (or line in) muted I have ups and downs in the spectrum line within +-10dB. I see on the picture of jayadev even up to 30dB curls. The question that rises is how it is possible to make decent spectral measurement with such a poor setup? It is such a mess even when no signal is applied...
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Old 25th October 2013, 01:25 PM   #8
jayadev is offline jayadev  India
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Quote:
Originally Posted by SY View Post
I'll try to remember to compose a decent reply later today when I'm not rushed.
Will be waiting .

I am still in wonderment why they give Dbfs for an analogue audio analyse.
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Old 25th October 2013, 06:15 PM   #9
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Didn't you try the RightMark Audio Analyzer? That is more popular tool for soundcard testing/benchmarking.

Anyways, what is exact model of your sound device and how much did it cost?
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Old 25th October 2013, 07:47 PM   #10
Eldam is offline Eldam  France
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Pirat of Carabians: RTA & ARTA are goods softwares...don't think it's the softs but the lake of method from us !

Without injecting signal with soundcard or rec with its digital source : what is a normal curve with such equipment in a room if not flat?

Is it noise of the pre sound card or/and non calibrating correction curve of the mic applied in the soft ?
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