Noise Level In Hi-Speed Modes - RME Audio ADI-2 Pro User Manual

34.5 Noise Levels in Hi-Speed Modes
The outstanding signal to noise ratio of the ADI-2 Pro AD-converters can be verified even with-
out expensive test equipment, by using record level meters of various software. But when acti-
vating higher sample rates, the displayed noise level will rise from -120 dBFS to -114 dBFS at
96 kHz, and –92 dBFS at 192 kHz. This is not a failure. The software measures the noise of the
whole frequency range, at 96 kHz from 0 Hz to 48 kHz (RMS unweighted), at 192 kHz from 0
Hz to 96 kHz.
When limiting the measurement range from 20 Hz to 20 kHz (so called audio bandpass) the
value would be -120 dB again. This can be verified with RME's DIGICheck. The function Bit
Statistic & Noise measures the noise floor as Limited Bandwidth, ignoring DC and ultrasound.
The reason for this behaviour is the noise shaping technology of the analog to digital convert-
ers. They move all noise and distortion to the in-audible higher frequency range, above 40 kHz.
Therefore the noise is slightly increased in the ultrasound area. High-frequent noise has a high
energy. Add the quadrupled bandwidth, and a wideband measurement will show a significant
drop in SNR, while the human ear will notice absolutely no change in the audible noise floor.
As can be seen in the next picture, the noise floor stays at a remarkably low level even outside
the hearing range. At sample rates of up to 96 kHz the noise shaping happens completely out-
side of the transmission range.
User's Guide ADI-2 Pro © RME
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