User Manual

User's Guide Fireface UFX II © RME
101
37.5 Technical Background
Compared to a usual computer, the front USB port of the UFX+ has a limited buffer to compen-
sate for interruptions to the write process. Unfortunately, these occur quite often with USB
thumb drives, and sometimes are of an astonishing duration. The effect of the buffer depends
on the amount of data to be transmitted, which is the combination of sample rate and channel
count. The higher the data rate, the shorter the available buffer time. When a medium causes a
pause that is longer than the buffer time, data is lost.
Information on the performance of the record media
To determine the highest record channel count of a hard drive or USB thumb drive the UFX II
displays several values. On the page Record/Playback:
USB Load: should exceed 80% only for a short time.
Errors: Each single error means a buffer with a bigger block of samples has been lost. Al-
though that is not always audible only a display of 0 is acceptable.
On the page USB Media, Record:
Max R/W Time (Read/Write Time): This constantly updated value is the quickest way to identify
slow media that suffer from interruptions of the write process. Hard drives often show values in
the range of 100 ms, while thumb drives can reach more than 800 (!) ms.
Checking the performance of the record media
Every USB stick can be used for recording – but most are too slow to record more than a few
channels. While write rates higher than 10 MB/s are rare, simultaneous quick processing of
recorded data is even less frequently found.
To determine the maximum channel count of a medium, activate all 76 record channels at a
sample rate of 48 kHz. This configuration causes the highest data throughput (10.7 MB/s) with
the smallest internal buffer. Most hard drives manage an error-free recording until the drive is
full. In case the UFX+ shows errors, reduce the number of channels step by step until no errors
are shown anymore.
Note
: 15 channels at 192 kHz equal 30 channels at 96 kHz and 60 channels at 48 kHz (8.4
MB/s).
A more realistic example is the recording of all 30 inputs and of two submixes (34 channels) at
48 kHz. With 4.8 MB/s data transfer better USB sticks will handle this task without any problem.
The display of USB Load, Max Write Time and errors quickly reveals where the limit of the par-
ticular thumb drive lies.
Note
: Playback is usually not affected by the mentioned performance problems.
An example of a USB flash drive that handles the maximum transfer bandwidth error-free is the
SanDisk Extreme Memory, available in 16, 32 and 64 GByte. It worked without write pausing
under USB 2, and is lightning fast under USB 3 as well.