If you look at the DIN IMD (Test Tone: 250Hz and 8kHz mixed at an amplitude ratio of 4:1) graph on page 9, you will see that you have overdriven the input.
Reducing the signal level a little bit should eliminate this artifact. I have confirmed this with my M-Audio USB cards.
Thank you for your feedback.
We have tested it again with the same setting and confirmed the input did not clip. We got the same result as the one in our published report.
We have also changed the loopback cables, output volume and input gain.... but the results were more or less the same. The following screenshot shows a IMD DIN test with even lower input gain, but the result was the same.
It looks like there are two types of MobilePre in the market, one with a black front panel, the other with a blue front panel. The one we tested was of the former type. Not sure whether it made the difference. If you go to M-Audio's website, you will see a new type of MobilePre which is different from the above two.
We have tested it again with the same setting and confirmed the input did not clip. We got the same result as the one in our published report.
We have also changed the loopback cables, output volume and input gain.... but the results were more or less the same. The following screenshot shows a IMD DIN test with even lower input gain, but the result was the same.
It looks like there are two types of MobilePre in the market, one with a black front panel, the other with a blue front panel. The one we tested was of the former type. Not sure whether it made the difference. If you go to M-Audio's website, you will see a new type of MobilePre which is different from the above two.
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Thanks very much for taking the time to re-run the tests and report your results. Your software has certainly revealed an oddity with this card.
As I don't have this model, I can't test it. My other M-Audio cards showed this only when over-driven. I did not change the input gain, but lowered the driving signal to prevent clipping. Perhaps that's the difference?
As I don't have this model, I can't test it. My other M-Audio cards showed this only when over-driven. I did not change the input gain, but lowered the driving signal to prevent clipping. Perhaps that's the difference?
In one of our tests, the output volume was adjusted to -20dB (we had to increase the input gain in order to maintain the final input signal level in order to achieve sufficient measurement accuracy), but the result was still the same. There are LEDs on MobilePre's panel to indicate clipping condition. During our test, we did make sure these LEDs were off.
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