It is very simple: let me describe it first. Two dividers and an XOR gate.
This is an FLL and only the frequency consistency is guaranteed but in this
case is enough. The advantage is that only a CPLD is used. I'll send the
VHDL so that it will be possible to use any CPLD. It is possible to
implement a real PLL but in my version an external OP-AMP is needed as I
prefer the UP/DOWN output to be combined externally .

On Fri, Jul 6, 2012 at 9:05 PM, Bill Dailey docdailey@gmail.com wrote:

There is a profesional "standard" for clock distribution for computer audio
interfaces.  They call it a "Word Clock" and it is usually distributed over
75 ohm coax cable.  It is common for a studio to have a master word clock
generator and to use audio interfaces that accept an external clock.  Some
of these master clocks have rubidium or OCXO inside.  Most can also PLL to
any external clock

The trouble is that lower priced audio interfaces lack a "word clock" input
and you'd need to get into something like this as a minimum to have that
feature
828mk3Hy http://www.sweetwater.com/store/detail/828mk3Hy/

So if you are going to hack a cheap consumer interface it might be a better
hack to install a word clock input.  At some point inside the interface
there MUST be a sample rate clock running at 44.1, 48, 96, 192 kilohertz.
Find then cut that trace and bring it out to a 75 ohm BNC connector.  Now
you have a standard pro level feature.

Now when you divide down your 10Mhz lab standard divide it to "word rate"
and you only need to build the divider once and you can use it with any
audio interface that has word clock I/O.

Yes of course you can send 14.4356MHz or whatever but that is a one time
design and it will be different with every audio interface depending on
whatever TTL can oscillator the engineer used.

All that said.  I have a "cheap" Presonus firewire audio interface that has
S/PDIF input and it has the option to accept word clock over the fiber
s/pdif.  Many low priced interfaces can do this.  Then you happen to have
a quality s/pdif device around you are set.

On Fri, Jul 6, 2012 at 12:05 PM, Bill Dailey docdailey@gmail.com wrote:

--

Chris Albertson
Redondo Beach, California

On 07/07/2012 04:10 AM, Chris Albertson wrote:

In professional audio settings, you distribute clock over AES/EBU (AES
3), which is the original interface that was budgetized into the
S/P-DIF. The preferred way is to distribute it over a quite channel
(much like the black burst video signal) and then you get a Digital
Audio Reference Signal (DARS) which is specified in AES 11.

A particular trick of receiving the clock is to use the end of the Y
symbol, as this would have the Y symbols known pattern as a preamble and
hence lowering the inter-symbol-interference quite dramatically.
The X/Z symbol still identifies the start of the frame, but being
isochronous it's predictable from the Y frames as well.

Use AES/EBU whenever you can. It's been designed to handle long
distances, something which was compromised out of S/P-DIF as it was only
intended to wire together consumer equipment on short distances.

Cheers,
Magnus