[opendtv] Re: News: Nielsen Gives Fuzzy Picture of HDTV Penetration
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Thu, 8 Nov 2007 11:05:46 -0500
Ken Hunold wrote:
> Since when were AM studios not "high fidelity?" High
> Fidelity is admittedly a weasel-word, but every AM
> station I've ever been involved with had frequency
> response much better than 5kc.
But they can't transmit that much quality, especially not at night,
because they can't exceed their 10 KHz spectrum. Some AM stations are
allowed to extend out to 30 KHz during the day, but of course there are
virtually no AM receivers that can use that much bandwidth. They would
have to have adjustable RF and IF stages to be able to go hifi during
the day, and then avoid enormous interference problems at night. So
other than a few communications receivers, I don't know of any AM radios
for consumer use that have this adjustable bandwidth feature. Analog AM
radios typically roll off at about 3 KHz.
Seems that people often overlook that in AM, the RF channel bandwidth is
exactly the same as the audio frequency response (above and below the
carrier). And dynamic range is abysmal, like around 35 dB tops. Unlike
in FM, where RF channel bandwidth is more directly related to the audio
dynamic range. And were it not for the stereo subcarrier, the frequency
reponse (potential) extends out to at least 75 KHz in mono FM.
I posted recently on this site that the FCC was now allowing digital AM
stations to extend out to 30 KHz even at night. The difference there is
that those digital sidebands are very suppressed compared with the
analog, like around 30 dB down.
> Similarly, when were television aural exciters not
> "high fidelity?"
While local TV had decent sound even back in the 1960s, basically the
same as FM radio but much less dynamic range (due to the 50 KHz
bandwidth of TV audio), Network TV shows sounded no better than AM
radio. Then suddenly, around 1976 or 1977, I noticed almost overnight
that all network TV shows sounded identical to the local transmissions.
Audio bandwidth out to around 15 KHz or so.
To get back on topic, then, while it might be true that not everyone
rushed out to buy hifi sound sstems for their TVs, better sounding TV
audio did eventually happen. Not JUST stereo, which came in the mid
1980s. The trend has been to good audio for TV, where TV audio used to
be very poor indeed in the past. ATSC goes further by offering 5.1
channel sound, for example.
These are all examples of how innovations are introduced. HDTV is the
same thing. The only thing to keep HD transmissions from overtaking
every program stream is the desire to conserve on bandwidth, to cram
more programs in the allotted channels. So it will be a balancing act,
but not for reasons Craig mentions, IMO. There's no reason to keep from
using HD other than to juggle the number of programs you can fit in the
channel.
Bert
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