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16.4 DS - Double Speed
When activating the Double Speed mode the M-32 DA 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 (Sample Multiplexing) in connection with the ADAT format.
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.
Because the ADAT interface does not allow for sampling frequencies above 48 kHz (a limitation
of the interface hardware), the M-32 DA automatically uses Sample Multiplexing in DS mode.
Two channel's data are combined into one channel according to the following table:
ADAT Port
1
DS Signal
1/2
Analog Out
1
As the transmission of double rate signals is done at standard sample rate (Single Speed), the
ADAT outputs still deliver 44.1 kHz or 48 kHz.
16.5 QS – Quad Speed
An implementation of the ADAT format as double S/MUX (S/MUX4) results in only two channels
per optical output. There are few devices using this method.
In Quad Speed mode the M-32 DA automatically uses Sample Multiplexing. Four channel's
data are combined to one channel according to the following table:
ADAT Port
1
QS Signal
1/2/3/4
Analog Out
1
As the transmission of quad rate signals is done at standard sample rate (Single Speed), the
ADAT output still delivers 44.1 kHz or 48 kHz.
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User's Guide M-32 DA © RME
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