Here is a plot showing the IM performance of the RTX. I'm using my set of Victor oscillators. They are all separately battery powered. This is 11.2 KHz + 12 KHz. First is an EMU 1212M with opamp upgrades, second is the RTX. Both use the same ADC. Clearly the analog circuitry on the EMU is not giving the AK5394A its best. The RTX performance is exceptional.
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I am wondering whether USB cable differences will show up or not in these measurements.
In my experience with USB audio sound cards, generally 30cm USB cable length will give the most balanced sound. Longer cabling with give more bass but the sound is not as clear; shorter cables will give less bass and more fatiguing sound. If this can show up in measurements, it would certainly be helpful.
I have tried the Xonar U7 and the Meridian explorer. These are USB powered devices. Both end up with the same cable length.
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I did a bunch of tests with cables from 12" to 100' and found no differences in response, distortion or jitter. However in the real world there are a lot of issues around conducted noise and USB. The direct ground can couple a lot of noise if there is a loop for it. That can bring the sonic results you mentioned.
Those different cables are here somewhere and I'll dig them out to see if there is an impact. It will take a few days to find them and free up some time.
Those different cables are here somewhere and I'll dig them out to see if there is an impact. It will take a few days to find them and free up some time.
Sorry- its 50M or about 150' Corning optical USB cable. It works fine. This is an extreme example. I have a long copper USB 2 cable here as well. That will be a separate adventure to find.
In any case RMAA loopback at 192/32 no issue and flawless results except on the tests that never work.
I just found and hooked 3 6' copper extension cables to it and still no issues.
hidden deep
That is the point.
I expect that distortion harmonics that barley poke above the noise floor of a large sample size, many times averaged FFT will be hidden deep in the residual of a time based waveform.
DT
That is the point.
I expect that distortion harmonics that barley poke above the noise floor of a large sample size, many times averaged FFT will be hidden deep in the residual of a time based waveform.
DT
Larry I'm not sure I get this:
First of all, I would think that the diff mode signal is:
yd = yp-ym = x+ax^2+bx^3 - (-x+ax^2-bx^3) ... but that is just a typo.
Now he assumes that the for ym, the signal is -x+a(-x)^2+b(-x)^3 but I would think, being the inverse of the original signal it actually is:
-x-ax^2-bx^3.
Then Yd = x+ax^2+bx^3 - (-x-ax^2-bx^3) = 2*(x+ax^2+bx^3) as we surely know.
In other words, when the distortion is already in the signal that is inverted to make it balanced, there is no cancellation at all. There is only possible cancellation if the distortion is different in the two phases, and in that case it does not make a difference whether it is odd or even because the cancellation results from subtraction in the diff receiver.
Or have I jusyt increased the confusion factor? ;-)
Jan
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I don't think that is true as a generality. If I have two signals with distortion products at opposing phase and similar amplitude, and I add those signals, the distortion products will cancel whatever their cause.
Jan
I wouldn't expect the USB cable length to make any difference, as long as data comes across without errors:
1. The converter clocks are generated locally, close to the converters.
2. The USB is isolated from the chassis.
Demian, good thing that the 50m cable was not a standard USB cable
I wouldn't expect that to work.
I think normally USB shielding ground and it's capacitance is probably interacting with the analog section of the sound card. Since the RTX runs from it's own power supply, it will not be an issue. I was planning to use the RTX to measure USB powered sound cards and see whether differences can be measured when different USB cables are used.
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Not really, it really took a while to come to the 30cm selection. The difference was very obvious to me. At
the same length, different brands could have some very slight difference, but not as much as length differences. The only thing now is to figure out whether there is a way to more clearly identify the difference though measurements. This is what I plan to do when I get my RTX.
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the same length, different brands could have some very slight difference, but not as much as length differences. The only thing now is to figure out whether there is a way to more clearly identify the difference though measurements. This is what I plan to do when I get my RTX.
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I really don't know exactly what I would look for, but I probably would start from looking at wavelet spectrograms. Looking at the harmonics over the full spectrum would probably also be useful. These are accessible in SoundEasy. However, I need to use an earlier version to get it to work with my USB cards.
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Jens, did you also test the prototypes for microphonics? For I understand that SMD parts sometimes can be sensitive to shock and/or vibration when soldered onto a PCB..
Since you strive for high resolution in the measurements, microphonics might become an issue under certain circumstances.
Since you strive for high resolution in the measurements, microphonics might become an issue under certain circumstances.