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27.5 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.
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 format
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 (Single
Speed), the MADI ports still operate at 44.1 kHz or 48 kHz.
27.6 SteadyClock
The SteadyClock FS technology of the HDSPe MADI guarantees an excellent performance in all
clock modes. Thanks to a highly efficient jitter suppression, refreshes and cleans up any clock
signal, and provides it as reference clock at the word clock output.
SteadyClock has been developed to
gain a stable and clean clock from the
heavily jittery MADI data signal. The
embedded MADI clock suffers from
about 80 ns jitter, caused by the time
resolution of 125 MHz within the format.
The picture to the right shows the MADI
input signal with 80 ns of jitter (top
graph, yellow). Thanks to SteadyClock
this signal turns into a clock with less
than 2 ns jitter (lower graph, blue).
The other input sources of the HDSPe
MADI, word clock, Video and LTC, gain
a lot from SteadyClock as well.
The signal processed by SteadyClock is used internally, and is therefore also available at the
word clock and the MADI output of the HDSPe MADI.
User's Guide HDSPe MADI © RME
78
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