Ds - Double Speed; Qs - Quad Speed - RME Audio HDSPe AIO Pro User Manual

27.3 DS - Double Speed

Sample rates above 48 kHz were not always taken for granted, and are still not widely used be-
cause of the CD format (44.1 kHz) dominating everything. Before 1998 there were no receiv-
er/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.
Because the ADAT interface does not allow for sampling frequencies above 48 kHz (a limitation
of the interface hardware), the HDSPe AIO Pro automatically uses the Sample Multiplexing
method 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 deliv-
er 44.1 kHz or 48 kHz.
The SPDIF (AES) output of the HDSPe AIO Pro provides 88.2 kHz and 96 kHz as Single Wire
only.
27.4 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.
Because the ADAT interface does not allow for sampling frequencies above 48 kHz (a limitation
of the interface hardware), the HDSPe AIO Pro automatically uses the Sample Multiplexing
method in QS mode. One channel's data is distributed to four channels (S/MUX4), which limits
transmission to 2 channels per optical port. Physically the ADAT output still operates at 44.1 kHz
or 48 kHz.
The SPDIF and AES output of the HDSPe AIO Pro provide 176.4 kHz and 192 kHz as Single
Wire only.
User's Guide HDSPe AIO Pro © RME
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