Dan.Strassberg dan.strassberg@att.net
Thu Oct 4 16:45:51 EDT 2007

I was under the impression that in FM-band HD, the aggregate bit rate
of the main channel plus all ND-n channels was limited to 96 kbps. As
a result, the main channel could either be 32 or 48 kbps and if the
main channel is 32, the HD-2 and HD-3 channels would each also be 32.
If the main channel was 48, HD-2 and HD-3 would each be 24. I also
heard that the single channel of AM HD is 24. I don't think that
anyone has proposed four 24-kbps channels per station on FM, but if my
figures are correct (and if they aren't, can somebody please correct
me), each of the channels would have the same bandwidth as the single
channel on the AM-band version.

Now, the HD codecs are allegedly superior to those use in Webcasts. I
am listening to a mono 48-kbps Web stream as I type this; it's Danny
Stiles from WNSW (the link is at www.dannystiles.com). Other than
Stiles' voice, the material--lots of old records from the 30s, 40s,
50s, and 60s--probably doesn't have even as much as 5 kHz of audio
bandwidth. I find it hard to believe that a stereo HD stream at the
same 48-kbps rate could have bandwidth any narrower than what I'm
listening to. If it did, I think it would sound so bad that nobody
would be likely to listen. But I suspect that it would be quite a feat
to squeeze the same audio bandwidth into a STEREO stream at half of
the bit rate of the mono stream I am listening to.

I've had DSL service for less than a week. A moment ago, I experienced
my first dropout; dropouts are much less common than with dialup. When
the DSL signal came back, however, the bit rate had increased from
1184 kbps to 1248. It's probably my imagination, but the audio
bandwidth of the stream may have improved when the signal returned.
Don't ask me to explain that because 48 kbps is a small fraction of
both 1184 and 1248.

Dan Strassberg (dan.strassberg@att.net)
eFax 1-707-215-6367

----- Original Message ----- 
From: <mike@miscon.net>
To: <boston-radio-interest@rolinin.bostonradio.org>
Sent: Thursday, October 04, 2007 11:45 AM
Subject: WCAI on WGBH HD

> Apparently, yesterday afternoon (Wednesday 10/3),
> listeners throughout WGBH's 89.7 coverage area with HD radios could
> receive WCAI on WGBH's HD3 channel.
> The premise is that WGBH launched this as a test of the extended HD
> mode to determine if the HD3 signal would interfere with WGBH's main
> signal.
> Presently, WGBH's HD channels are:
> HD1: main 89.7 signal (48kbs)
> HD2: all classical (48kbs)
> HD3: WCAI (24kbs)
> Just thought some of you 'd want to
> know...
> Mike

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