[vdr] Re: spdif and DD receiver

["Dr. Werner Fink" <werner@suse.de>]

On Thu, Jul 24, 2003 at 02:16:47PM +0200, Andreas Holzhammer wrote:
> I want to avoid an optical link at all cost, having heard the difference 
> between optical and coaxial connections. I know there should not be any, 
> but there are, and optical does sound "cold".

Hmmm.............  technical the 48kHz  two channel 16 bit PCM stream is
transported within 32bit words for every 16 bit word.
There are alway used a group of 192 32bit words (frames) together for each
channel with special start bits within each preamble of every 32bit word
to ensure the correct frame detection and parity check.   To ensure the
synchroneity a biphase mark code (BMC) signal is used with a clock twice
as fast as 48kHz.

It upon the receiver to detect out of this BMC system the correct clock
speed for decoding and replaying ... regardless of the physical transport
way.  The only difference is the natural phase variation (so-called jitter)
of the source which may be declared by high end PCM sources within the 192
status bits of the 192 32bit transport frames ... but this is an other story.
Other jitter _should_ be solved by receiver due buffering with the help of
the well defined clock within the BMC system, as well as by using good
cables (coax or optical).

    -> http://www.epanorama.net/documents/audio/spdif.html
    -> AES3 (IEC 60958, ISO 646)

This is clearly a technical and cold definition, even for 75 Ohm coax ;^)


        Werner


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