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Because the HDSPe MADI is a completely digital interface, and the delays introduced by exter-
nal AD/DA-converters or other digital interfaces are unknown to unit and driver, the drivers in-
clude the digital offset values (3 / 6 / 12 samples). Therefore the delays caused by external con-
verters have to be taken care off in the record software, which usually means that the user has
to enter specific offset values manually.
Note: Cubase and Nuendo display the latency values signalled from the driver separately for
record and playback. The current driver includes a safety offset of 32 samples for the playback
side only, which will be included in the shown value.
Safety Buffer
An additional small safety buffer on the playback side has proven to be very efficient and useful.
It is therefore implemented in all RME interfaces. Under Windows the HDSPe MADI uses a fixed
additional buffer of 16 samples, under Mac 32 samples, which is added to the current buffer
size. Main advantage is the ability to use lowest latency at highest CPU loads.
Core Audios Safety Offset
Under OS X, every audio interface has to use a so called safety offset, otherwise Core Audio
won't operate click-free. The HDSPe MADI uses a safety offset of 24 samples. This offset is
signalled to the system, and the software can calculate and display the total latency of buffer
size plus offset plus safety offset for the current sample rate.
27.4 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 multichannel
ADAT format. The AES3 specification uses the uncommon term Single channel double sampling
frequency mode.
With MADI, sample multiplexing is often used as well to offer sample rates higher than 48 kHz.
The HDSPe MADI 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 MADI distributes the data of one channel to two consecutive MADI channels. This re-
duces the available channel count from 64 to 32.
As the transmission of double rate signals with 48K Frame is done at standard sample rate (Sin-
gle Speed), the MADI ports still operate at 44.1 kHz or 48 kHz.
User's Guide HDSPe MADI © RME
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