Owner's Manual

8
Cambridge
Audio
Operating instructions cont.
Advanced
USB
audio
The
851C is both
USB
2.0
(Hi-Speed) and
USB
1.1
(Full-speed)
USB
port
compatible.
It should also
work with the new
USB
3.0
ports where the
PC
will simply
treat the 851C as if
it were a
USB
2.0
or 1.1 device.
The
851C
also
supports two
USB
Audio
protocols (not the same as the
port types
themselves)
USB
Audio
1.0
(which works over
USB
1.1 ports
and supports up to 24-bit/96kHz) or
USB
Audio
2.0
(which requires a
USB
2.0
port and can support up to 24-bit/192kHz).
The
default
configuration
is
USB
1.1 and
USB
Audio
1.0
which works
with
nearly all
common operating systems and computer types without
drivers and supports up to
24
-bit/96kHz audio, simply plug
in and
play.
In
this configuration the 851C
is
able
to work at up to 24-bit/96kHz
by
declaring
to your computer
that
it
can
handle any sample
rate from
32kHz to 96kHz.
However
in
some Windows/Mac operating system variants the operating
system
itself
may restrict or
fix
the output
sample
rate or re-sample
the
audio.
See
our
online
guide
at
www.cambridge-audio.com/851CSupport
on
USB
Audio for more details
on
this. With
careful
choice
of
playback
software and settings many
pitfalls
can be avoided.
In
particular our free Windows
USB
Audio
2.0
driver
(available
from our
website) supports up to 24-bit/192kHz audio and
WASAPI
Exclusive
or
ASIO
modes
that
can give enhanced performance.
See
the
Setup section
on
how to switch between
USB
Audio
1.0
and
2.0
modes.
A brief explanation
of
your choices are
below:
Use with
PCs
With the 851C switched to
USB
Audio
1.0
(this
is
the
default setting) the
851C
will
work with the native Windows
XP,
Vista or 7 Audio
1.0
driver
(no need to
load
any new driver) and accept audio up to 24-bit/96kHz.
With the 851C switched to
USB
Audio
2.0 the 851C needs the Cambridge
Audio
USB
Audio
2.0
Driver
to
be
loaded
and can then accept up to
24-bit/192kHz (and support
ASIO
and
WASAPI
Exclusive
if required).
The
driver
is
available
from www.cambridge-audio.com/851CSupport.
Use
with Macs
No
extra drivers are required. With the 851C switched to
USB
Audio
1.0
the 851C
will
work with the native Mac
OS-X
10.5
(Leopard) or above
Audio
1.0 driver and accept audio up to 24-bit/96kHz.
With the 851C switched to
USB
Audio
2.0 the 851C works with the native
Mac
OS-X
10.5
(Leopard) or above Audio 2.0
driver and can accept audio
up to
24
-bit/192kHz.
Use
with Linux
For
most
builds
of
Linux with the
851C
switched to
USB
Audio
1.0 the
851C will work with the native Audio
1.0
driver and accept audio up to
24-bit/96kHz.
Some
very new
builds
of Linux are now supporting
USB
Audio
2.0
for
which the 851C
should
be switched to Audio
2.0
to accept audio up to
24-bit/192kHz.
For
both cases because Linux
builds
vary according to their creators
choice
of
software components
including drivers it is not possible to
guarantee operation and Audio drivers may need to
be
loaded.
'Class
drivers' as they are
called
for generic support
of
Audio Class 1.0
or Audio
Class 2.0
devices may be
available
from the Linux community,
we do not supply these.
10
Bit perfect transfer -
ASIO
and
WASAPI
Exclusive
mode
The
851C
USB
interface hardware and software support bit perfect
transfer.
Whether or not the audio sent to the
851C
is
bitperfect
(i.e.
not resampled
or mixed etc.
by
the
PC)
is
actually
a function of the
playback application
'
and the operating systems audio engine.
By
default
the standard windows audio drivers (often
called
WDM
drivers)
included
in Windows
XP
support MME or DirectSound transfer,
both of which include a
kernel mixer and re-sampler stage.
One
way
round this is to use
ASIO
to bypass this. Another
is
to use a
playback application
that
supports its own form of
kernel streaming,
i.e.
if has its own
way
of outputting the audio without invoking the kernel
mixer.
For
Windows
Vista and Windows 7 a new method
of
audio transfer
is
supported
called
WASAPI.
This has two modes; Shared and
Exclusive.
Shared mode
is
similar to MME or DirectSound but
in
Exclusive
mode the
kernel mixerjre-sampler
is
bypassed and bit perfect transfer
is
possible
with
only
one audio playback program directed to the soundcard at a
time (for instance system sounds are not mixed in).
To
ensure bit perfect transfer use a playback
application
that supports
ASIO,
WASAPI
in Exclusive
mode (if
you
have Windows
Vista
or Windows
7)
or some form of kernel streaming.
This
is
a fast moving area so
we
would
encourage
you
to check the
web
for the
latest media players to support these more audiophile playback
options.
To
use
ASIO
you
will
need the Cambridge Audio Sound Driver
installed
and
the
851C
switched to
USB
Audio
2.0.
No
further settings are required as the driver automatically
_§iupports
ASIO
transfer,
all
that
is
required is to load
and setup
suitable
ASIO
enabled playback software.
ASIO
(Audio Stream
Input/Output)
is
a non Microsoft audio driver
protocol for Windows
originally invented
by
Steinberg
ltd
ASIO
bypasses
some
of
the
normal
audio path from the playback
application
through
the Windows audio system (including the Kernel Mixer) for a more direct
path
to
the
851C.
You
will
need to
install
and use a suitable playback application
that supports
ASIO
output either natively or
via
a plugin.
One
example
of
such
an
application with a suitable plugin
is
Foobar, see
http:/
jwww.foobar2000.org
for more details.