User Manual

User’s Guide OctaMic XTC © RME
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27.4 USB Audio
USB audio is in several ways different from PCI based audio interfaces. An OctaMic XTC can
achieve a performance similar to a PCI or PCI Express card when used with an optimal PC.
Low CPU load and click-free operation even at 64 samples buffer size are indeed possible on
current computers. However, using older computers a simple stereo playback will begin to
cause a CPU load of more than 30%.
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 (and with this the la-
tency).
The OctaMic XTC features a unique data checking, detecting errors
during transmission via USB and displaying them in the Settings
dialog. Additionally the OctaMic XTC provides a special mechanism
to continue recording and playback in case of drop-outs, and to
correct the sample position in real-time.
Like any audio interface the OctaMic XTC should have a data transmission to the computer as
undisturbed as possible. The easiest way to guarantee this is to connect it 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 Manager can be done as follows:
¾ Connect the OctaMic XTC to a USB 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 OctaMic XTC. By recon-
necting to a different port this view immediately shows at which of the two controllers the Oc-
taMic XTC is connected. With multiple devices it can also 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 OctaMic XTC, by simply connecting the drive to the other controller. The information is also
valid for USB 3 ports.
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.