S/PDIF Input and Output
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 Mac OS.
Input
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. The input selection LED flashes without
S/PDIF connection and turns solid when a valid S/PDIF source is connected. Mac
OS Sound Manager will truncate data higher than 16-bit to 16-bit. Using ASIO
drivers, up to 24-bit audio can be input into the computer. See Mac
ASIO for additional information.
Be certain to match the sample rate of the S/PDIF input with the
corresponding configuration file of the same sample rate, otherwise
objectionable distortion will be present. For instance, select a 48 kHz sample
rate configuration file (see Configuring the
USBPre) when accepting a 48 kHz S/PDIF signal.
Output
Macintosh Sound Manager is limited to a maximum of 16-bit output. To output
greater than 16-bit audio, ASIO drivers are require. With Sound Manager audio
file greater than 16-bit will be truncated to 16-bit.
The Macintosh Sound Manager continuously outputs S/PDIF clock data at 44.1
kHz, even when no audio is present. Therefore, all audio played back through
the USBPre S/PDIF output is at 44.1 kHz. This means that audio files different
than 44.1 kHz go through a sample rate conversion in the operating system
before being sent to the USBPre. For many applications, this is acceptable,
however, you may want to change this output sample rate to transfer 32 kHz or
48 kHz files at their respective rates. Contact Sound Devices at usbpre@sounddevices.com
for the latest information on how to force Sound Manager to sample rates other
than 44.1 kHz.
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