User's Manual

User’s Guide ADI-2 DAC v2.2 © RME
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17. DSD
17.1 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 DAC supports DSD in various ways. When received via 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 functions
possible on a bit stream. Therefore EQ, Crossfeed, Bass/Treble, Loudness and other audio
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 176.4/192 kHz for DSD64, 352.8/384 kHz for DSD128, and 705.6/768 kHz
for DSD256. Under 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 as well as ASIO native. ADI-2 DAC therefore is compatible to many
programs, like HQPlayer, and JRiver, but also to DSD recording software like Merging's
Pyramix, Sound-It and VinylStudio.
17.2 DSD Direct
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
DAC’s menu (SETUP - Options), the analog signal is available only at the rear outputs, with a
coarse volume control via the analog output reference level control. Outputs Pones and IEM
deactivated.
In DSD Direct mode the output level for digital full scale is 3.5 dB lower than with standard DSD
mode. Therefore the maximum analog output level is 3.5 dB lower than the chosen reference
level. For a valid comparison between DSD and DSD Direct the volume of DSD should be set to
-3.5 dB.