RME Audio MADIface XT, Руководство пользователя

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User's Guide MADIface XT
© RME
30.4 USB Audio
USB audio is in several ways different from PCI based audio interfaces. Thanks to the high
speed of
USB 3
, typical problems of streamed (isochronous) data transmission can be circum-
vented. RME’s proprietary USB 3 technology makes it possible to achieve performance similar
to PCI Express,
IF
all participating components work perfectly. At this time USB 3 has got a bad
reputation because many layouts, cables and connectors are designed badly and lower the
maximum throughput. Typical problems are not or randomly detected devices, devices that fail
as soon as data is transmitted, transmission errors and following (as required by the USB 3
standard) the reset of the host controller, guaranteeing a drop out for several seconds.
It is therefore not possible to guarantee reliable and highest performance of USB 3 operation
with any computer and cable just because they support USB 3. The real performance has to be
evaluated on a per USB 3 port (!) and per cable base.
To make this as easy as possible, and to quickly signal problems, RME added an
extensive
error detection and analysis
into the MADIface XT hardware, detecting errors during transmis-
sion via USB 2 and 3, and displaying them in the Settings dialog. Additionally the MADIface
provides a special mechanism to continue recording and playback in case of drop-outs, and to
correct the sample position in real-time.
While some errors shown here might not cause audible
clicks and do not stop record/playback, the golden rule
applies:
only zero errors are acceptable
. If errors show up
use a different USB 3 port and exchange the USB 3 cable.
Never use USB 3 cable extensions!
Current MADIface XT USB 3 Compatibility Information
¾ Fully compatible to
Intel's USB 3
implementation which - on current Windows and Mac
computers - is part of the chipset. USB 3 sockets that are connected via an internal cable
(not directly soldered onto the motherboard) can cause transmission errors (shown in the
Settings dialog).
¾ Fully compatible to
AMD's USB 3
implementation. USB 3 sockets that are connected via an
internal cable (not directly soldered onto the motherboard) can cause transmission errors
(shown in the Settings dialog).
¾ Compatible to
NEC / Renesas USB 3
. Real-world performance and error-free operation
depend on the firmware version, driver version and the PCB layout of the respective exten-
sion card/motherboard.
¾ Fully compatible to
Fresco USB 3
chip.
¾
ASMedia
- not compatible
¾
Etron EJ168A
- not compatible
¾
Texas TUSB7340
- not compatible
¾
Via VL800/805
- not compatible
The MADIface XT is capable of using two different transmission modes to record data. The XT
defaults to
Bulk Mode
, which improves reliability of USB 3 audio tremendously and helps with
both less than perfect cabling as well as critical layouts around the USB 3 chip. The standard’s
default is
Isochronous Streaming
, which is unreliable as per the standard (errors are to be ex-
pected!), unreliable in real-world operation, and not correctly supported by popular USB 3 chips.
In very seldom cases, bulk mode can not keep up with the strict timing required for continuous
audio streaming. Then, to make the XT work at all, isochronous mode must be used (but is still
prone to clicks and drop-outs). To make the standard mode available as reference, firmware
versions higher than 160 enable the activation of the isochronous mode in the Settings dialog.
The MADIface XT also supports
USB 2
. Good performance and click-free operation even at low
buffer sizes are indeed possible on current computers. However, using older computers a sim-
ple stereo playback might cause a CPU load of more than 30%.