In article , tony sayer

wrote:


Pending some other topics that Jim Lesurf bought up which I'm awaiting
the time and equipment to all be in the same place,

[snip]

Since you mention the above, the following comments may also be of
interest... :-)

I did a search through the JAES I have and much to my surprise I couldn't
find a computation of the level of nominal distortion for 'Zenith' stereo
as a result of the limited transmission bandwidth. Anyone know if this has
been published? I would have assumed it had, but I suppose that working
this out 20+ years ago would have been a pain due to the computational
requirements.

To save me re-inventing the wheel I've also been looking for a textbook
which I recall had worked out the sidebands for FM modulation with two
components. (Nearly all texts avoid anything more than a simple sinewave
modulation as an example for fear of the maths involved. :-) ) This would
at least be closer to L-R modulation than simply using an HF sinewave as a
test. Alas, not yet found the text I can recall reading - admittedly it was
about 10 years ago! :-)

I've been doing some estimates based on single-frequency modulation, but
not yet satisfied with the results as I'm not happy with the Bessel
appoximations I used - although it behaves in general terms as I'd
expected.

If I get a chance, sometime soon I'll do a better analysis and report the
results. Might make an interesting comparison with your measurements, Tony.
:-)

For simplicity, I'd tend to assume a 'top hat' filter with a 240 kHz
transmission bandwidth, whereas in reality the filtering will have sloped
sides (and an imperfect inband response). Hence I'd expect an analysis and
the measured results not to be identical, but should share similar levels
and trends.

BTW Was looking at the manual for the CT7000 and that shows a plot of TDH
versus modulation depth for a 400Hz mono modulation which goes up to well
over 100%! This is useful as it shows the bandwidth is more than +/-75kHz
as you'd expect, but they give no data for HF L-R modulation.

BTW2 the topic of level compression came up on R4's 'Feeback' last week.
combined with a throw-away comment about DAB... :-)

Slainte,

Jim

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