On 11/05/15 9:36 PM, Charles Belov wrote:
On 11/5/15 10:45 AM, Patty Winter wrote:
In article ,
Charles Belov wrote:
KCBS 740 San Francisco "simulcasts" on KFRC-FM 106.9. I put simulcast in
quotes because I notice the broadcast coming from KCBS is about one
second behind KFRC-FM. This is a consistent behavior over many months,
not something randomly happening on a particular day.

Is there a legal or technical reason why this might be the case?

It would be technical. First question: are you listening to an analog
or digital radio?

BTW, you might increase your chances of someone who knows the situation
responding if you post your question to the Bay Area broadcasting groups,
ba.broadcast and ba.broadcast.moderated.


Patty


Thank you for the recommendation; cross-posted to the two Bay Area
groups. The radio is analog. I can switch between a stored AM station
(740) and a stored FM station (106.9) instantly by pressing the AM or FM
button.

Charles, KCBS-AM and KFRC-FM not only simulcast, but they each have an
"HD" (aka IBOC) digital simulcast. (Their top-of-the-hour legal ID says
"KCBS-AM and HD, KFRC-FM and HD1, San Francisco" etc.) Because there is
a need to buffer the digital stream, a delay is introduced of around 8
seconds. Then in order not to jump forward or backward 8 seconds in time
as the receiving radio switches between analog and digital, stations
delay their analog audio by the equivalent 8 seconds later in their
audio chain, so the transitions are relatively seamless.

It may be that the delay between the AM version of IBOC has a slightly
different delay than the FM version, which would account for the one
second difference. Few stations simulcast on AM and FM, but even fewer
are running HD on AM anymore. KCBS is the exception in the Bay Area, and
because of that the difference in delay is noticeable. (I've also
noticed that one second delay difference when switching between 740 and
106.9 in my analog car radio, and I hear the switch-to-digital and
fall-back-to-analog phenomenon in cars with HD radios.)

Maybe one of our colleagues in this group would be willing to get deeper
into the weeds about this.