RME Audio Fireface UFX+, Руководство пользователя

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User's Guide Fireface UFX+ © RME 115
39.5 DS - Double Speed
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 (Sample Multiplexing)
in connection with the multichannel ADAT format.
With MADI, sample multiplexing is often used as well to offer sample rates higher than 48 kHz.
The UFX+ supports all formats. 96 kHz can be received and transmitted both as 48K Frame
(using S/MUX) and as native 96K Frame. In 48K Frame Double Speed mode, the UFX+ distrib-
utes the data of one channel to two consecutive MADI channels. This reduces the available
channel count from 64 to 32. As the transmission of double rate signals with 48K Frame is done
at standard sample rate (Single Speed), the MADI ports still operate at 44.1 kHz or 48 kHz.
Because the ADAT interface does not allow for sampling frequencies above 48 kHz (a limitation
of the interface hardware), the Fireface UFX+ automatically uses
Sample Multiplexing
in DS
mode. One channel's data is distributed to two channels. As the transmission of double rate
signals is done at standard sample rate (Single Speed), the ADAT outputs still deliver a 44.1
kHz or 48 kHz carrier.
39.6 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.
An implementation of the ADAT format as double S/MUX (S/MUX4) results in only two channels
per optical output. Devices using this method are few.
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.
With MADI, sample multiplexing is used as well to offer sample rates higher than 96 kHz. In
fact, technical reasons require to use this method beyond 96 kHz. A 192K or 384K Frame for-
mat would not be fully compatible to the MADI standard. Therefore 192 kHz is supported as
S/MUX4 only. So in 48K Frame Quad Speed mode, a MADI device distributes the data of one
channel to four consecutive MADI channels. This reduces the available channel count from 64
to 16.
As the transmission of quad rate signals with 48K Frame is done at standard sample rate (Sin-
gle Speed), the MADI ports still operate at 44.1 kHz or 48 kHz.
Because the ADAT interface does not allow for sampling frequencies above 48 kHz (a limitation
of the interface hardware), the Fireface UFX+ automatically uses
Sample Multiplexing
in QS
mode. One channel's data is distributed to four channels. As the transmission of quad rate sig-
nals is done at standard sample rate (Single Speed), the ADAT outputs still deliver a 44.1 kHz
or 48 kHz carrier.