RME Audio ADI-2 DAC, User Manual

Page: 62 / 68

62 User’s Guide ADI-2 DAC © RME
The following measurement shows a digital full-scale sine of 1 kHz, 16 bits without dither, which
is reduced in level by 40 dB. Also shown are a full-scale sine of 1 kHz with 24 bit, at 60 dB and
96.3 dB level attenuation, which is the lowest volume setting the ADI-2 DAC offers.
A high-resolution FFT like HpW Works makes it possible to disassemble the signal into
individual frequencies, and to identify unwanted components down to a level of -190 dBFS. The
measurement shows that the undithered 16 bit signal does not produce any distortion or other
tones above -170 dBFS. So at a volume setting of -40 dB the measurable THD is -130 dB. At 24
bit a volume setting of -60 dB also achieves -130 dB without distortion. And at a volume setting
of -96.3 dB there are still -93 dB THD measurable.
These results clearly show that distortion products of the digital volume control are not drowned
by the DAC's noise, but are not generated at all. It works perfectly even with an undithered 16
bit signal, no detectable distortion products are produced.
If the volume control is measured at the analog output, the demonstrable THD is reduced to
around -100 dB at a volume setting of -60 dB, by the self-noise of the DAC (SNR 117 dB RMS
unweighted). In the above measurement that would be seen as straight noise floor at -160
dBFS. The digital volume control of the ADI-2 DAC therefore works much more precisely and
cleaner than required for current top-level DACs.
In summary:
RME's digital volume control in 42 bit TotalMix technology avoids all the disadvantages of
analog level control via pots, is easy to use, offers reproducible settings, and the highest sound
quality.