User guide

100
User's Guide MADIface XT © RME
30.4 USB Audio
External PCI Express is the professional’s solution for an external audio interface which should
work as good as possible – and like an internal one. This includes Thunderbolt, which basically
is PCI Express. Using a Thunderbolt to PCIe adapter box is both valid and does not degrade
performance.
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 or do not apply anymore as they did with USB 2. RME’s proprietary USB 3 technology
makes it possible to achieve performance similar to PCI Express, IF all participating compo-
nents 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, guar-
anteeing 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 easy as possible, and to quickly signal possible problems, RME added an exten-
sive error detection and analysis into the MADIface XT hardware, detecting errors during
transmission 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 cable extensions!
A computer blocked for a short time – no matter if ASIO or WDM – will lose one or more data
packets. Such problems can only be solved by increasing the buffer size (latency).
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 will begin to cause a CPU load of more than 30%.
Best USB 2 performance is achieved by connecting the XT to its own bus, which should be no
big problem as most USB 2.0 interfaces are a double bus design. A check in the Device Man-
ager can be done as follows:
Connect the MADIface to a USB 2 port
¾ Start the Device Manager, View set to Devices by Connection
¾ Select ACPI x86-based PC, Microsoft ACPI-Compliant System, expand PCI Bus
This branch normally includes two entries of a USB2 Enhanced Host Controller. A USB Root
Hub can be seen, which then connects all USB devices, including the MADIface. By reconnect-
ing to a different port this view shows at which of the two controllers the MADIface is connected.
With multiple devices it can be checked if they are connected to the same controller.
Furthermore this information can be used to operate an external USB drive without disturbing
the MADIface, by simply connecting the drive to the other controller.
Especially with notebooks it can happen that all internal devices and all the sockets/ports are
connected to the same controller, with the second controller not used at all. In that case all de-
vices have to use the same bus and interfere with each other.