User's Manual

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User’s Guide ADI-2 DAC v2.2 © RME
31.12 USB Audio
An ADI-2 DAC can achieve a performance similar to a PCI or PCI Express based soundcard
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 ADI-2 DAC features a unique data checking, detecting errors
during transmission via USB and displaying them in the Settings
dialog. Additionally the ADI-2 DAC 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 ADI-2 DAC 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 ADI-2 DAC 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 ADI-2 DAC. By recon-
necting to a different port this view immediately shows at which of the two controllers the ADI-2
DAC 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 ADI-2 DAC, 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.
Experienced RME users remember the above text from the manuals of our other interfaces with
lots of channels. Compared to these the ADI-2 DAC has two advantages:
• It uses an isochronous audio stream of only two channels (pretty ridiculous)
• It is not necessary to work at lowest latency. Setting the ASIO buffers to their highest value
offers a much less critical and more stable recording and playback experience.
One should not underestimate the effect on higher sample rates with PCM and DSD, though.
Those require to transfer data of multiples of the amount typical for a channel at 48 kHz:
Base 48 kHz 96 kHz 192 kHz/DSD64 384 kHz/DSD128 768 kHz/DSD256
Channels 2 4 8 16 32