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34.10 Noise Levels in Hi-Speed Modes
The outstanding signal to noise ratio of the ADI-2/4 Pro SE AD-converters can be verified even
without expensive test equipment, by using record level meters of various software. But when
activating higher sample rates, the displayed noise level will rise from about -121 dBFS to -118
dBFS at 96 kHz, and –115 dBFS at 192 kHz, etc. 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.
The doubled or quadrupled bandwidth results in a reduced signal-to-noise ratio for a wideband
measurement, while the audible noise component does not change in the slightest. When limiting
the measurement range from 20 Hz to 20 kHz (so called audio bandpass) the value would be -
121 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 ADC used in the ADI-2 Pro shows, like almost all converters do in an FFT, an increase of
noise above 40 kHz. This leads to -92 dBFS noise floor in the above wideband measurement.
The ADI-2/4 Pro SE uses the ES9822Pro, which besides sensationally low distortion close to full
scale level will show no increase in noise up to 200 kHz. So up to a sampling frequency of 384
kHz the measurement will show an even, very low noise floor. These excellent characteristics
make the ADC ideal for measurement purposes
Note: As is common in professional Digital Audio Workstations, the level meters of the ADI-2/4
Pro SE are band limited to 45 kHz. They will not show the extreme noise levels of 768 kHz and
DSD, but everything within the audio range and a bit above.
User's Guide ADI-2/4 Pro SE - v 1.0
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