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Old 14th August 2012, 06:39 PM   #11
TheGimp is offline TheGimp  United States
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One other consideration when running distortion tests is to limit the bandwidth. I'm not familiar with ARTA, but in Audio Tester one can set the lower and upper limit for the distortion calculations.

This is helpful if you are getting a lot of line power related noise in your measurement as you can set the lower bound to say 400Hz and upper bound to 20KHz and eliminate the LF and HF noise.
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Old 14th August 2012, 07:23 PM   #12
Salas is offline Salas  Greece
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When in SPA mode there is a low cut off tick box in setup/spectrum scaling plus IEC weighing options.
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Old 19th August 2012, 08:51 AM   #13
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Thanks everyone for your comments and help.

On many analog spectrum analyzers you can place markers at key spots on the trace. The markers display precise measurements that can compare with other markers.

My next question is, does ARTA (or any of the other popular software programs) provide this capability?

I know you can move the cursor to a point of interest, annotate the reading and then move to another point of interest.
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Old 19th August 2012, 09:38 AM   #14
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Regarding the 2nd and 3rd harmonics in the loopback test - try reducing the master output volume and/or the record level in the sound mixer application. On many sound cards running both at maximum will increase harmonic distortion significantly.

On my Soundblaster Audigy 2 ZS I set both to about -1 to -2dB to avoid this. Try adjusting the sound mixer sliders while in the real time analyser mode and see if you notice a sudden drop in the harmonics as you turn the output or input levels down slightly.

I would echo 5th elements advice regarding sticking to native sample rates - it looks like 48Khz is being resampled, so I would avoid that altogether. I do all my measurements in 96Khz 24bit regardless of whether the test needs the bandwidth or not, just to be sure I'm running in a native sample rate with a known calibration.

Although my card also supports 48Khz 16bit natively the amplitude calibration is different, which means if you're doing calibrated measurements you'll need to re-verify calibration if you change sample rates. Just stick to one native sample rate and you'll be fine...
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Last edited by DBMandrake; 19th August 2012 at 09:40 AM.
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Old 19th August 2012, 12:24 PM   #15
tvrgeek is offline tvrgeek  United States
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I found out the hard way, exceeding 0 dB on the Audigy wound increase distortion permanently. This is why I am now running an M-Audio Profire if you get my drift!
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Old 21st August 2012, 10:37 AM   #16
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Quote:
Originally Posted by DBMandrake View Post
Regarding the 2nd and 3rd harmonics in the loopback test - try reducing the master output volume and/or the record level in the sound mixer application. On many sound cards running both at maximum will increase harmonic distortion significantly.

On my Soundblaster Audigy 2 ZS I set both to about -1 to -2dB to avoid this. Try adjusting the sound mixer sliders while in the real time analyser mode and see if you notice a sudden drop in the harmonics as you turn the output or input levels down slightly.
If reduced the Master output and record levels I can reduce the harmonics. But I thought the goal was to increase the levels to peak the 1khz tone somewhere close to -3 dBFS. I thought I read that somewhere in the ARTA manual. It would seem to me that one would have to establish a consistent reference level from one measurement to the next.

Is my thinking on this wrong?

Please be patient with me, I learning.
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Old 21st August 2012, 10:40 AM   #17
ODougbo is offline ODougbo  United States
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ohhh need to jump on this thread....I downloading (easy) now what?
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Old 21st August 2012, 03:12 PM   #18
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If lowering the signal/record levels by a couple of dB results in a significant drop in THD then that is fine. I mean of course you are going to lower the absolute signal to noise ratio by a little, but as long as you are aware of this then it isn't a problem.

Doug, ARTA is fairly user friendly, if you've just downloaded it I recommend you play with to familiarise yourself with the menus etc.
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Old 21st August 2012, 08:10 PM   #19
TheGimp is offline TheGimp  United States
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Has anyone compared ARTA to AudioTester? If so how did they compare on features and ease of use?

At some point the input will exceed the acceptable input for all of the audio interfaces, and they will begin clipping. When they do your distortion will go up, and no longer represent the input signal.

With the M-192 the threshold is a bit over 2.8Vrms.
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Old 21st August 2012, 09:07 PM   #20
ra7 is offline ra7  United States
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I was having a strange problem using the XMOS USB2.0 Eval board with ARTA. In Spectrum Analyzer mode, it measures superbly, less than 0.0045% THD. But in impulse mode, I can't get it to do a full 20 Hz - 20 kHz sine sweep. The sweep doesn't produce any sound until after 1 kHz. Now, if I set the averaging to 2 or more, then the second sweep begins at 20 Hz, but the first one still comes out as no sound until above 1 kHz. And funnily enough, the pink noise seems to work fine.

Also, ARTA starts doing all sorts of funky things, like showing two impulses, one after the other, when really there should be one averaged impulse from 2 sweeps. I've put it down to the async clock on the XMOS that ARTA cannot get a good handle on. I read in the documentation that is designed to work with Synchronous cards only.

Any thoughts?

Oh btw, same problem with Holm. So, it's definitely the soundcard.

Last edited by ra7; 21st August 2012 at 09:12 PM.
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