Traditionally,
soundcards worked with audio streams in an inflexible signal
routing mode.
X-Fi introduces a
flexible
ring-architecture
which provides advanced signal routing features, supporting
up to 4096 (internal) audio channels.
This allows for
advanced processing of audio streams in differing routing
patterns.
S-SRC
If you have read any of
our previous soundcard reviews you will have noticed how we
often comment on resampling. Creative soundcards have been
often criticized for the quality of their 44.1 kHz
resampling which added noticeable distortion. This process
has now been given a much requested overhaul; in fact,
Creative believes it is so good they called it
Super-Sample
Rate Conversion. A sizable portion of the DSP has
been dedicated to the task, which operates in 3-steps:
The source sample rate
is doubled, e.g. 44.1 kHz -> 88.2 kHz.
A poly-phase FIR
(Finite Impusle Response) filter (256
available) is used to convert this to 4 x Desired sample
rate, e.g. if 48 kHz is the desired sample rate, 88.2 kHz is
upsampled to 192 kHz (48 kHz x 4).
This sample is finally
reduced by a factor of 4, e.g. 192 kHz -> 48 kHz.
Creative notes that in
tests they used a
997Hz tone (at
44.1 kHz), and converted it to 48 kHz, yielding a THD+N of
better than -135dB, with as little as +/- 0.00025dB of
pass-band ripple. Even under less than ideal conditions this
still performs better than high quality DACs do.
Additionally, when running in Audio Creation mode it
is possible for the X-Fi to function without performing
resampling at all (more on that later).
Overall, Creative’s work
in this area means they finally have cast of their
resampling issues, and it has now become an advantage of
their soundcards.
