Hey there,

Does anyone know if it is possible to control the output clock of a
soundcards S/PDIF output?

I have an M-Audio Audiophile usb soundcard with co-ax digital out and
am experimenting with different audio clock rates.

Could I control the clock by writing a program in C for example? The
sound card must have a local address on the USB bus - are the ports
easily addressable/accessible?

Any advice/help greatly appreciated! Cheers, Alex.

Hi Alex,

According to the manual, the device supports 44.1, 48, 88.2, and 96Khz via
the S/PDIF I/O. These rates are selectable via the standard Win MME/DirectX
API via c. To do anything else would require a great deal of hacking.
First step would be to open the box and see if the chips are marked and are
off the shelf devices. If so, you would need to study the datasheets to see
if the hardware was capable. Finally, you would have to hack or write new
Win device drivers. Quite a task.

Mark
"mr_alex" wrote in message
ups.com...
Hey there,

Does anyone know if it is possible to control the output clock of a
soundcards S/PDIF output?

I have an M-Audio Audiophile usb soundcard with co-ax digital out and
am experimenting with different audio clock rates.

Could I control the clock by writing a program in C for example? The
sound card must have a local address on the USB bus - are the ports
easily addressable/accessible?

Any advice/help greatly appreciated! Cheers, Alex.

"mr_alex" wrote in message
ups.com
Hey there,

Does anyone know if it is possible to control the output
clock of a soundcards S/PDIF output?

Depends on the drivers. Some support a variable clock rate, given
appropriate driver software.

I have an M-Audio Audiophile usb soundcard with co-ax
digital out and am experimenting with different audio
clock rates.

What application software are you using for recording?

Could I control the clock by writing a program in C for
example? The sound card must have a local address on the
USB bus - are the ports easily addressable/accessible?

Probably, if you can the appropriate documentation.

But, you may not need any special software at all. Some recording software
will record at any sample rate that fits in the supported range, and so can
some soudcards.

Thanks for all the info - it does look like a tall order and one that I
will keep experimenting with.

Does anyone know the actual format of the digital data output? Is it
I2S? Or something similar - the IC I need the data fed to accepts Left
Justified, Right Justified, I2S or DSP Serial data formats...

Cheers, Alex.

"mr_alex" wrote:

Hey there,

Does anyone know if it is possible to control the output clock of a
soundcards S/PDIF output?

That depends on the card. I have both a MIA-24 from Echo Audio and a
USB Transit from M-Audio. The latter is rather new to me.

The MIA can be switched to external clocking (clock must be supplied
via S/P DIF input as there is no clock input) and uses that clock even
if it does not match the output data. Thus you can play back a 96/24
file using a 44.1 input signal. The playback cursor in Adobe Audition
looks weird while putting out data too slowly.

I have an M-Audio Audiophile usb soundcard with co-ax digital out and
am experimenting with different audio clock rates.

Both the MIA and the USB Transit got their firmware loaded when the
driver initializes the card. Maybe your card gets the firmware loaded
down as well. So you have in theory the potential to hook changes
there.

Could I control the clock by writing a program in C for example? The
sound card must have a local address on the USB bus - are the ports
easily addressable/accessible?

What do you want to achieve?
Playback at varying speeds?
Playback of odd sample rates?
Helium speech?
Playback infra sonic sounds?

Norbert

"mr_alex" wrote in message
ups.com
Thanks for all the info - it does look like a tall order
and one that I will keep experimenting with.

Does anyone know the actual format of the digital data
output? Is it I2S? Or something similar - the IC I need
the data fed to accepts Left Justified, Right Justified,
I2S or DSP Serial data formats...

Look up SP/DIF on google.

mr_alex wrote:
Thanks for all the info - it does look like a tall order and one that I
will keep experimenting with.

Does anyone know the actual format of the digital data output? Is it
I2S? Or something similar - the IC I need the data fed to accepts Left
Justified, Right Justified, I2S or DSP Serial data formats...

S/P-DIF is officially enshrined in IEC 60958. It's pulse code modulated
linear two-channel data. Each sample period the interface is presented
with a sample frame. Each sample frame is made up of two subframes,
each subframe is a 32-bit structure where the first 4 bits are the sync
bits,
data is held in the next 24 bits as two's comlement left-justifed audio
sample data,most often with the low-roder 8 bits being unused, and the
remaining 4 bits being used for sample parity, sample validity,
channel
status and user status. 192 frames are collected together as a block,
at which time the 192 channel status bits are availabel as 24 8-bit
channel status words holding sample rate, copyright protection status,
original info, sample size and other information. The underlying
encoding
is as a biphase stream, and the 4 bit header of each subframe violates
the biphase criteria to signal a data object start..