Technical Background - Nuendo DD8 Operation Manual

11. Technical Background

11.1 DS - Double Speed
When activating the Double Speed mode, the Nuendo DD 8 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 receiver/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 car-
ries one channel, of which the odd and even samples are being distrib-
uted to the former left and right channels. By this, you get the double
amount of data, i. e. also double sample rate. In order to transmit a
stereo signal two AES/EBU ports are necessary then.
This transmission mode is being called Double Wire in the professional
studio world, and is also known as S/MUX in connection with the ADAT
format. The DTRS recorder DA-98HR by Tascam also uses this tech-
nique, which is called Dual Line here.
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 re-
corders. But also other common interfaces like ADAT or TDIF are still us-
ing this technique.
Because the ADAT interface does not allow for sampling frequencies
above 48 kHz (a limitation of the interface hardware), the Nuendo DD 8
automatically uses a technique called Sample Split in DS mode. One
channel's data is distributed to two channels according to the follow-
ing table:
Original
DS Signal
Port
NUENDO DD 8
English – 38
1 2 3
1/2 3/4 5/6
MAIN MAIN MAIN
4 5 6
7/8 1/2 3/4
MAIN AUX AUX
7 8
5/6 7/8
AUX AUX