Perreaux SILHOUETTE SXD2 - Manual (Page 17)

16
Block
Diagram
USB
Connectivity
The SXD2 is fully compliant with USB 1.1 specification and
utilises ‘Full Speed’ (12Mbps) transceivers. The bandwidth
offered by ‘Full Speed’ USB is more than sufficient to stream
digital audio.
Plug and Play Designed to bypass the inherently flawed soundcards internal to
computers, the SXD2 offers plug and play convenience when
connected via the USB port.
BNC Digital
Input
Connector
RCA connectors are inherently disadvantaged for use with the
high frequency (1.4MHz-2.8MHz) signals associated with
44.1kHz/16-bit digital audio. Design limitations mean RCA
connectors can never achieve a characteristic impedance of 75Ω,
resulting in reflections and signal loss due to impedance
mismatch. In contrast, BNC connectors are purposely designed
to carry high frequency signals, up to 2GHz for 75Ω – therefore
overcome the problems exhibited by RCA connectors.
Up-Sampling The SXD2 automatically up-samples the digital signal 4x the
input sample frequency, up to a maximum of 192kHz. For
example, if the digital input is 44.1kHz (CD), the SXD2 will up-
sample to 176.4kHz (4x 44.1kHz).
Rather than offer constant up-sampling to 192kHz, we have
purposely decided to use a multiple of the input frequency (4x).
This guarantees that every 4
th sample will be true. Using
44.1kHz sample frequency as an example, if it were up-sampled
to 192kHz, then only every 640
th
sample would be true to the
original 44.1kHz signal.
24-bit
Resolution
Red Book Audio CDs have a sampling rate of 44.1kHz and 16-
bit resolution. This results in a maximum possible Signal-to-
Noise Ratio (SNR) of around 96dB. Increasing the resolution to
24-bit not only reduces quantization error in signal amplitude,
but also increases the maximum possible SNR to around 144dB.