General; Direct Dsd - RME Audio ADI-2 Pro User Manual

19. DSD

19.1 General

DSD (Direct Stream Digital) is a stream with single bit resolution, but multiple times the sample
rate of the CD. DSD64 equals 64 times 44.1 kHz = 2.8 MHz, DSD128 5.6 MHz, DSD256 11.2
MHz. Versions with multiples of 48 kHz also exist, up to 12.2 MHz.
To transfer DSD data over SPDIF, AES or even USB, DSD over PCM (DoP) is the de-facto
standard. It uses only the lower 16 bit of a 24 bit word, the upper 8 bit are filled with a DoP
header signal to be able to detect it, and to lower the overall volume to prevent damage in case
of accidental playback as PCM data. Note that the data stays pure DSD and is NOT converted
to PCM.
The ADI-2 Pro supports DSD in various ways. When received via AES or SPDIF, the State
Overview screen will show DoP, and the DAC immediately turns from PCM to DSD mode. The
process is transparent to the user, playback will continue as usual. But there are no DSP func-
tions possible on a bit stream. Therefore EQ, Crossfeed, Bass/Treble, Loudness and other au-
dio functions provided by the DSP are deactivated. This is shown by adding brackets to the
activated function, for example EQ Enable - (ON).
The DoP recognition also works on USB. A DSD playback via USB (State Overview shows
DSD) will be done at 192 kHz for DSD64, 384 kHz for DSD128, and 768 kHz for DSD256. Un-
der Windows WDM/WASAPI are currently limited to 384 kHz. The highest sample rates and
DSD modes can only be used via ASIO. RME's driver supports DSD over ASIO in DoP format.
The so-called ASIO native mode is currently not supported.
19.2 DSD Direct (Playback only)
To be able to digitally adjust the volume, DSD data must be converted to PCM. This is done
automatically within the DA converter chips. In DSD Direct mode there is no PCM conversion –
and consequently no volume control anymore. After having activated DSD Direct in the ADI-2
Pro's menu (SETUP - Options), channels 1/2 use this mode when a DSD signal is received.
The analog signal is then available at the rear outputs, with a coarse volume control via the
analog output reference level control. Outputs PH 1/2 are deactivated. Outputs PH 3/4 stay in
normal DSD mode and have the standard volume control available.
The output level for digital full scale is 3.5 dB lower than with standard DSD mode. Therefore
the maximum analog output levels are 3.5 dB lower than the reference values. For a valid com-
parison between DSD and DSD Direct the volume of DSD should be set to -3.5 dB.
In mode DSD Direct headphones can not be used.
User's Guide ADI-2 Pro © RME
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