User`s guide

18
User's Guide ADI-8 DS © RME
9.5 DS - Double Speed
When activating the Double Speed mode the ADI-8 DS operates at double sample rate.
The internal clock 44.1 kHz turns to 88.2 kHz, 48 kHz to 96 kHz. With this the device is able to
process even ultra-sound above 40 kHz at its analog inputs and outputs. AD/DA-converter and
COPY mode still use full 24 bit resolution.
The ADAT optical interface does not support sample rates above 48 kHz. Therefore the con-
verter uses a Sample Split method, which operates similar to the BIT SPLIT function. Single
channel data is split to 2 channels according to the following table:
Original 1 2 3 4 5 6 7 8
DS Signal
Port
1/2
MAIN
3/4
MAIN
5/6
MAIN
7/8
MAIN
1/2
AUX
3/4
AUX
5/6
AUX
7/8
AUX
This method of transmitting double speed data at single speed is known as double wire
throughout the professional audio world, and also known under the name S/MUX regarding
ADAT interfaces. Tascam also uses this method in their latest DTRS recorder DA-98HR, but
calls it Dual Line.
The table is valid for all directions (AD - DA - DD). As the AUX port is already used for DS the
function BIT SPLIT is not available simultaneously.
As the transmission of double rate signals is done at standard sample rate (Single Speed) the
word clock output still delivers 44.1 kHz or 48 kHz. The same is true for the word clock input,
where only 44.1 kHz or 48 kHz are expected.
The wordclock input and output as well as all ADAT and TDIF ports always operate in Sin-
gle Speed mode only. At 96 kHz, the word clock output will therefore be a 48 kHz signal.
The TDIF interface of the ADI-8 DS also supports the 'Double Wire' technique. This allows
a recording with up to 96 kHz at halfed track numbers with every (!) DTRS device.
Note: The ideal combination is an ADI-8 DS together with the digital I/O card RME Hammerfall
Light (DIGI9636). This allows to simultaneously record and playback 8 tracks at 24 bit/96 kHz,
using PC or Mac.
9.6 Noise level in DS operation
The outstanding signal to noise ratio of the ADI-8 DS can be verified even without expen-
sive test equipment, by using our famous DIGICheck tool or the record level meter of WaveLab
3.0. When activating the DS mode the displayed noise level will rise from -113 dB to -100 dB.
This is not a failure. This kind of measurement measures the noise of the whole frequency
range, at 96 kHz from 0 Hz to 48 kHz (RMS unweighted). When limiting the measured area to
22 kHz (audio bandpass, weighted) the value would be -110 dB again.
The reason for this behaviour is the noise shaping technology used in the ADI-8 DS’ ana-
log to digital converters. They move all noise and distortion to the in-audible higher frequency
range, above 24 kHz. That’s how they achieve their outstanding performance and sonic clarity.
Therefore the noise is slightly increased in the ultrasound area. High-frequent noise has a high
energy. Add the doubled bandwidth (which already lowers the measured SNR by 3 dB), and a
wideband measurement will show a drop of 10 dB in SNR, while the human ear will notice ab-
solutely no change in the audible noise floor.