RME Audio Hammerfall HDSPe RayDAT, User Manual

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User's Guide HDSPe RayDAT
© RME
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30.3 DS - Double Speed
When activating the
Double Speed mode the HDSPe RayDAT operates at double sample rate.
The internal clock 44.1 kHz turns to 88.2 kHz, 48 kHz to 96 kHz. The internal resolution is still
24 bit.
Sample rates above 48 kHz were not always taken for granted, and are still not widely used
because of the CD format (44.1 kHz) dominating everything. Before 1998 there were no re-
ceiver/transmitter circuits available that could receive or transmit more than 48 kHz. Therefore a
work-around was used: instead of two channels, one AES line only carries one channel, whose
odd and even samples are being distributed to the former left and right channels. By this, you
get the double amount of data, i. e. also double sample rate. Of course in order to transmit a
stereo signal two AES/EBU ports are necessary then.
This transmission mode is called
Double Wire in the professional studio world, and is also
known as S/MUX (abbreviation for Sample Multiplexing ) in connection with the ADAT format.
The AES3 specification uses the uncommon term Single channel double sampling frequency
mode .
Not before February 1998, Crystal shipped the first 'single wire' receiver/transmitters that could
also work with double sample rate. It was then possible to transmit two channels of 96 kHz data
via one AES/EBU port.
But
Double Wire is still far from being dead. On one hand, there are still many devices which
can't handle more than 48 kHz, e. g. digital tape recorders. But also other common interfaces
like ADAT or TDIF are still using this technique.
Because the ADAT interface does not allow for sampling frequencies above 48 kHz (a limitation
of the interface hardware), the HDSPe RayDAT automatically uses the
Sample Multiplexing
method in DS mode. One channel's data is distributed to two channels according to the follow-
ing table:
Original 1 2 3 4 5 6 7 8
DS Signal
Port
1/2
ADAT1
3/4
ADAT1
5/6
ADAT1
7/8
ADAT1
1/2
ADAT2
3/4
ADAT2
5/6
ADAT2
7/8
ADAT2
As the transmission of double rate signals is done at standard sample rate (Single Speed), the
ADAT outputs still deliver 44.1 kHz or 48 kHz.
The SPDIF and AES/EBU I/Os of the RayDAT operate in Single Wire mode only.
30.4 QS – Quad Speed
Due to the small number of available devices that use sample rates up to 192 kHz, but even
more due to a missing real world application (CD...), Quad Speed has had no broad success so
far. An implementation of the ADAT format as double S/MUX (S/MUX4) results in only two
channels per optical output.
In earlier times the transmission of 192 kHz had not been possible via Single Wire, so once
again sample multiplexing was used: instead of two channels, one AES line transmits only one
half of a channel. A transmission of one channel requires two AES/EBU lines, stereo requires
even four. This transmission mode is being called
Quad Wire in the professional studio world,
and is also known as S/MUX4 in connection with the ADAT format. The AES3 specification
does not mention Quad Wire.