On Tue, 15 Jan 2008 09:51:38 -0800, Ron D'Eau Claire wrote:
> Many AM stations today limit their audio bandwidth to 5 or 6 KHz,
> maximum, and even more consumer AM receivers sold today limit the
> audio bandwidth to 5 kHz or less!
> Some of the reasons for the limits at the transmitter have to do
> with going to digital audio. I haven't worked in the broadcast
> industry since digital AM started to appear so I don't know the
> overall issues, but I see it mentioned regularly in the
> broadcasting press.
Yes, it has to do with what is known as the NRSC Mask which was
adopted in preparation for AM digital transmissions to confine
the analog signal within a 10 kHz linearized channel. A lot of
older transmitters and antenna array tuning units ("phasers")
had to be retuned or replaced in order to meet the NRSC linearity
requirements.
> A few articles I've seen in the broadcast press even note that
> since almost 1/2 of the American public under 50 years of age is
> now functionally deaf above about 6 or 7 KHz, thanks to abusing
> their ears with loud music as children, they are completely
> unaware of the change in audio response anyway.
How very true.
--
73 de K2ASP - Phil Kane
Elecraft K2/100 s/n 5402
Philip M. Kane P.E. / Esq
VP - General Counsel & Engineering Manager
CSI Telecommunications Inc. - Consulting Engineers
San Francisco, CA - Beaverton, OR
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