(Robert Orban) wrote in message ...
Since the HDC codec provides 15 kHz bandwidth in stereo, while analog AM
stereo is limited to perhaps 9.5 kHz (given an ideal receiver and
understanding the absolute need for a 10 kHz carrier-beat filter), the
digital signal will sound far better to anyone whose hearing acuity
extends to 15 kHz, which is the bandwidth commonly accepted as being
necessary for an impression of high fidelity.
Judging by the samples on...
http://www.wor710.com/Engineering/ib...io_samples.htm
....and from current tends in audio coding, it's almost certain that
the HDC codec is using spectral band replication. In which case, all
that bandwidth up to 15kHz is fake. There's a genuine 5kHz or 7.5kHz
audio bandwidth, and the rest is synthesised. Quite badly, to my ears.
The digital signal will also have a noise floor in excess of 90 dB below
100% modulation, making it immune to the static and manmade noise that
has caused so many problems on the band in the last few decades.
The fact that silence is silence will please some people, as will the
lack of crackle and hiss. But the (hopefully inaudible) coding noise
is only 20-30dB below the signal in a good, high bitrate
psychoacoustic codec. Things will be even worse in low bitrate digital
AM. I didn't know a 90dB dynamic range was part of Orban's business
plan? ;-)
Even disregarding the subtleties (of which there are many), these two
factors alone make HD AM dramatically superior to analog AM stereo.
Some people may be superficially pleased with the silence moments, and
bright sound. However, listening to the samples, it sounds really
quite nasty. IME, people can be very unforgiving of that kind of
artificial, metallic, "computer" sound.
btw - I'm in Europe, so can't listen to AM stereo, or IBOC HD radio
off air. Our digital AM plans, if any, seem to be based on DRM. I
doubt we'll see IBOC over here. It's sad that the world's radio
standards will probably be split in the same way that the world's TV
has been. That's if any consumers actually want digital radio at all.
Cheers,
David.
In article , says...
http://www.geocities.com/kevtronics