RME Audio ADI-192 DD, User Manual

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User's Guide ADI-192 DD © RME
11.3 DS - Double Speed
When activating the
Double Speed mode the ADI-192 DD 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 and newer interfaces
like ADAT or TDIF are still using this technique. And finally it can be used to transfer 192 kHz
using 96 kHz-capable equipment.
Since the ADAT and TDIF interface are not defined to operate beyond 48 kHz directly, the ADI-
192 DD uses sample multiplexing in DS operation. One channel's data is distributed to two
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
As the transmission of double rate signals is done at standard sample rate (Single Speed), the
ADAT and TDIF ports still operate at 44.1 kHz or 48 kHz.
The 'Double Wire' or 'S/MUX' technology of the AD-192 DD's TDIF interface allows a recording
with up to 96 kHz at halved track numbers with any (!) DTRS device, and is fully compatible to
Tascams DA98HR.
11.4 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 ADAT port.
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.