RME Fireface UCX II 40-Channel USB-B Audio/MIDI Interface - Manual (Page 105)

User's Guide Fireface UCX II © RME
105
The free software is available for Windows and Mac OS X and can be downloaded from the
RME website,
www.rme-audio.com , section Downloads / Software .
The Fireface UCX II adds some meta data to the recorded files, like date, time, recording device
and channel number. The WAV File Batch Processor reads these data and writes them accord-
ingly into the generated wav files. Additionally the processor adds the channel info to the file
names. For example UFX01_I_05.wav is the record data of input channel 5, and
UFX01_O_03.wav the recording of output channel 3.
38.5 Technical Background
Compared to a computer, the rear DURec USB port of the UCX II has a limited buffer to com-
pensate 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 UCX 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. Although
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. Quick media like SSD and hard
drives show values in the range of 80 to 100 ms at full channel count, while thumb drives can
show more than 800 (!) ms.
Checking the performance of the record media
Different USB based media can be used for recording – but USB thumb drivers, even USB 3.0
models, are often too slow to record more than a few channels.
To determine the maximum channel count of a medium, activate 16 channels at a sample rate
of 192 kHz. This configuration causes the highest data throughput (9.2 MB/s) with the smallest
internal buffer. Most hard drives manage an error-free recording until the drive is full. In case the
UCX II shows errors, reduce the number of channels step by step until no errors are shown an-
ymore.
Note: 16 channels at 192 kHz equal 32 channels at 96 kHz and 64 channels at 48 kHz (9.2
MB/s).
A more realistic example is the recording of all 20 inputs and of two submixes (24 channels) at
48 kHz. With 3.4 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.