]On Thu, Apr 12, 2007 at 11:31:12PM -0400, Richard A. Keirstead wrote:
> Actually, I got it at Best Buy: Insignia IS-HC040917. See:
> http://www.bestbuy.com/site/olspage.jsp?skuId=7016463&st=Insignia+IS-HC040917&type=product&id=1099394773266
> My understanding is that AC-3 is the same thing as S/PDIF which is the
> same thing as optical audio using a fiber optic cable called Toslink. So
> I did all that & still have no sound. The DW channel has no sound. No
> sound from optical, L&R audio, or RF. All other channels have normal
> sound via all the previously mentioned means.
All of this is quite wrong.
AC3 is an optional encoding method (licensed from Dolby Labs)
for DVB-S satellite audio. The standard DVB-S audio encoding is
Musicam and essentially all DVB-S receivers support that and can decode
it into analog audio internally, but only a rather few professional and
specialized DVB-S receivers contain AC3 decoders as the require patent
license costs manufacturers money.
AC3 encoded audio is a single serial digital bitstream that
contains all the audio channels multiplexed together along with some so
called metadata information describing the format. It is NOT an analog
signal and requires a decoder to convert the compressed digital signal
into multiple analog audio channels for input to amplifiers for speakers
or headphones.
It so happens, however, that AC3 audio is extensively used in US
entertainment electronics and is the encoding standard for digital ATSC
TV audio and a widely used format on DVDs. Thus much modern
multichannel home theater gear includes AC3 decoding built into AV
receivers and amps and computer sound cards so it is quite possible to
listen to AC3 encoded FTA DVB-S audio in the home if one's FTA receiver
outputs the AC3 bits to an external decoder such as a AV receiver.
The AC3 serial bitstream can be transmitted over a number of
different media, but standard in consumer electronics are two: fiber
optical (called TOSlink) with a red LED diode pulsed on and off to
represent the ones and zeros focusing its light over a multimode plastic
fiber, and serial coaxial with the bits on a coax cable as electrical
voltages The optical interface and the coax interface using RCA phono
plug connectors carry the same bit stream at the same rate, but
obviously involve different connectors and interfaces. It is possible
to convert from one to the other if needed using appropriate converter
boxes.
There is a standard for audio sent over optical or coax called
S/PDIF, and sending encoded AC3 is one legal (but not the only legal)
mode of using a S/PDIF interface to send audio.
Some consumer FTA DVB-S receivers recently marketed in the US
have provisions to output an AC3 bitstream when they see a DVB-S signal
carrying AC3. Some put this bitstream out on a RCA jack coax interface
and some use TOSlink optical. Very few if any consumer FTA receivers
contain decoders to convert the AC3 to analog audio internally, thus in
order to hear anything on AC3 encoded DVB-S signals one needs to feed
the AC3 bitstream to an external AC3 decoder such as a home theater
receiver using TOSlink or serial coax.
--
Dave Emery N1PRE, [EMAIL PROTECTED] DIE Consulting, Weston, Mass 02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in
celebration of what could have been, but wasn't and is not to be now either."
