RME Audio Hammerfall HDSPe AES, User Manual

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User's Guide HDSPe AES
© RME
30.4 DS - Double Speed
When activating the
Double Speed mode the HDSPe AES 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 multichannel
ADAT format. The AES3 specification uses the uncommon term Single channel double sam-
pling 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. With MADI, sample multiplexing is often used
as well to offer sample rates higher than 48 kHz.
The HDSPe AES 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 HDSPe
AES distributes the data of one channel to two consecutive AES channels. This reduces the
number of available channels from 16 to 8.
30.5 QS – Quad Speed
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.
The AES3 specification does not mention Quad Wire.
The HDSPe AES supports all formats. 192 kHz can be received and transmitted as 48K frame
(Quad Wire), 96K frame (Double Wire), and as native 192K frame. In 48K frame Quad Speed
mode, the HDSPe AES distributes the data of one channel to four consecutive AES channels.
This reduces the number of available channels from 16 to 4.