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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 stand-
ard. 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 acci-
dental playback as PCM data. Note that the data stays pure DSD and is NOT converted to PCM.
The ADI-2/4 Pro SE 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 functions
possible on a bit stream. Therefore EQ, Crossfeed, Bass/Treble, Loudness and other audio func-
tions 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-2/4 Pro SE therefore is compatible to many programs, like
HQPlayer, and JRiver, but also to DSD recording software like Merging's Pyramix, Sound-It and
VinylStudio.
19.2 DSD Playback
During a DSD playback all DSP functions of all channels are
temporarily disabled, even when transmitting PCM. This is
signalled in several menus by brackets around the (ON). An-
alyzer and level meter show DSD signals in a slightly different
color, the current mode is therefore easy to recognize.
The change between PCM and DSD causes a low volume
click noise. For optimized sound and fidelity, the ADI-2/4 Pro
SE does not use any lossy analog volume control, hence can't
suppress the DAC's click noise.
You may notice clicks and cracks at the title change quite often with DSD, even when the next
title has the exact same sample rate. This is caused by the 1-bit format, which, unlike PCM, re-
quires absolute silence and DC freedom at the beginning and end of a title, so that the transition
as required by the 1-bit stream does not represent a random signal, which can sound like a click
or crack. Unfortunately, many freely available tracks are not 'clean' at the beginning and the end.
If these are played back one after the other by player software, the ADI-2 DAC's level meters
show that the noise to be heard does not originate from the ADI-2/4 Pro, but is presented to the
unit as a signal to be played. The level meters are in the digital domain before the DAC, so proof
of a faulty input signal is easy.
Note: A DSD playback via USB is only supported on playback channels 1/2. A DSD64 playback
in mode Multichannel via USB 3/4 does not activate the DSD mode.
With DSD playback, the analog output level is identical to a PCM playback. However, DSD limits
Volume control to +2.5 dB, while PCM allows up to +6 dB.
User's Guide ADI-2/4 Pro SE - v 1.0
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