The switch from 44 to 48 kHz doesn't make much change in performance on a card of this type, which ought to show its best performance at any sampling frequency.
Frequency response : Unfortunately, the linearity of the response in extreme treble did not improve, but extended to a slightly higher level. Overall, the result remained very good.
Noise level : The result was noticeably identical to the (excellent) one obtained at 44 kHz.
Dynamic capacity : Here again, the figures were very close and excellent.
Distortion : No change with an initial harmonic that was already around -110 dB!
Intermodulation : Identical, excellent readings.
Stereo separation : The values remained very high. In practice there was zero diaphony.
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So, overall, the 1820 is guilty of having a frequency response marked with a very slight attenuation in the extreme treble. This is a matter of manufacturer choice, since the manufacturer opted for very low noise and excellent dynamics. There's nothing more to say: the 1820 is much better than mass-market sound cards and many competing cards for musicians. This would apply even more with a high-quality 1820M. As a reminder, the distortion is too slight to worry anyone and the diaphony is unlikely to interfere with your recordings!
