The USBPre can be used to transfer digital audio into and out of a computer
via its S/PDIF connections. Please read the following notes relating to S/PDIF
in Windows OS.
The USBPre can accept S/PDIF input sources at 16, 20, and 24-bit and with
sample rates of 32, 44.1, and 48 kHz. With Windows 98SE and Windows 2000 a
full 24-bit signal will be transferred. In Windows Me signals with bit depths
higher than 16-bit will be truncated to 16-bit. The input selection LED
flashes without S/PDIF connection and turns solid when a valid S/PDIF source
is connected.
Because of a limitation in Microsoft's kmixer system file in Windows 98SE,
2000, and Me, the output of the USBPre is limited to 16-bit. A 20 or 24-bit
signal sent to the USBPre will output 16-bit data.
To improve the transfer of digital audio, the USBPre Control Panel has an
S/PDIF output sync selection. With no sync selected devices connected to the
USBPre's S/PDIF output may take several seconds to "lock-up" to the
S/PDIF signal. During lock-up, objectionable audible artifacts are present.
When no audio is present the S/PDIF output is inactive. When an output sync
sample rate is selected in the Control Panel the S/PDIF output port is always
active, sending 0's at the selected sample rate when no audio is present. This
greatly improves the performance of transfers from the S/PDIF output, since a
lengthy pre-roll is not required to lock-up the data.
BIG NOTE: Selecting an output sync sample rate in the control panel
may have a negative on audio performance since all audio, regardless of its
native sample rate, will output at the selected sync rate. Sample rate
conversion will occur in Windows when the computer receives an audio signal at
a frequency that is different from the selected sync sample rate. Again, make
certain that the selected output sync sample rate matches the sample rate of
the files being played, otherwise sample rate conversion will occur.