Jim Barrett wrote: In order to hear surround audio on hi-def channels one must connect the cable box digital audio output (an optical connection) to the digital (optical) input of the AVR.
HOWEVER, commercials are not alway broadcast in digital audio so an analog connection must also be made via the red & white analog inputs, and non-hi-def channels have only analog so the AVR must then be set for autodetect with priority for a digital signal.
Jim Barrett wrote:NOW, when watching the hi-def channel program the digital audio works as expected with the front of the AVR indicating an optical audio signal. When a commercial comes on and the AVR front panel indicates a switch from optical to analog the speakers give a brief pop, like a speaker would do if you used a switch to cut it off when it was under load (sorry, I have no better way to describe it). At the end of the commercial the AVR switches from analog back to optical and the brief pop occurs.
Our AVR doesn't pop. The only indication that it has lost digital
audio is the change on the front panel display, and the collapse
of the surround sound field, usually to stereo.
Further, it takes at least a few seconds to resync each time,
and the audio is muted. We routinely clip the first few seconds
I'm surprised the advertisers don't complain about this loss of
delivery to their audience. (For a while I thought I was the only
one who'd noticed this problem).
Jim Barrett wrote:I have run across this business of the cable box HDMI not outputting audio and having to do this double cable business before but regardless, the AVR should switch with no noise.
What brand and model are the TV, AVR, and cable box?
What service provider feeds the cable box?
Jim Barrett wrote:When next I go over there I will take a different optical cable with me, just to rule it out (although why a digital signal in a fiberoptic cable should cause such a symptom is beyond me).
If it were a conventional cable I would think about hanging a 'scope in the line to determine whether the noise is comming from the cable box or not.
I've tried to isolate the problem by reconfiguring the various
cables and units in our current configuration. So far the problem
is systemic (loss of digital audio and delay while muting to switch
to stereo mode).
Jim Barrett wrote:My question involves an adapter or test jig that would allow one to look at the signal on the optical cable. Noise on that cable should be easily distiguishable from the signal. But, as I think about it, it's more likely the analog connection making noise than the digital.
This type of interface is not testable with general purpose gear.
In fact the limited work I've done on serial digital interfaces has
required BER (bit error rate) generators and pathalogical signals.
I posted on this topic last November, but made no progress. We've
decided to live with it.
More info here