Re: "Listeners don't want DAB"

"Peter Watson" <peter@xxxxxxxxxxx> wrote in message
news:7g060eF2nl1oaU1@xxxxxxxxxxxxxxxxxx
On 30/08/2009 16:48, steve41@xxxxxxxxxxxxxx wrote:
On Aug 30, 3:24 pm, "jamie powell"<jamie_...@xxxxxxxxxx> wrote:
"DAB sounds worse than FM"<dab...@xxxxxxxxxx> wrote in
messagenews:7fv04eF2mtj3cU1@xxxxxxxxxxxxxxxxxxxxx


Do you think that it'll make you look clever if you keep pasting
that
link?


Er, no. That happens to be a figure showing the FM multiplex
spectrum
- you don't get much more relevant a figure than that to a
discussion
of FM.


Shame the diagram you keep posting is wrong then isn't it? :)


It looks about right to me with regards to the stuff below 53 kHz,
which covers all the signals that have been discussed in this thread.

If you've found something wrong with the figure above 53 kHz, I'm
afraid I pity you for even mentioning it on here considering that that
stuff hasn't been mentioned at all, and it would simply highlight what
an incredibly pedantic fool you are.


Let's compare the operations required to get the mono signal:

My preferred method
===============

Mono signal is extracted by simply lowpass filtering the signal
at the
output of the FM demodulator

Not normally available as the demod stage is combined with the
decoder.
It is normal to 'turn off' the multiplex decoder so that the Left
and
Right outputs both carry mono


The mono signal will be available inside the chips used for DAB/FM
receivers (which is what we're discussing here, no?), because they use
software-defined radio to implement FM reception, and they have to
extract both the L+R and L-R signals prior to reconstructing the Left
and Right channels.

What you say would be plausible for analogue FM ICs, though, because
the bulk of sales will be for stereo FM chips.


Jamie's supposedly simpler method
========================

Extract the sum (mono) signal by lowpass filtering the signal at
the
output of the FM demodulator.
Downconvert the difference signal to DC and lowpass filter the
signal.
Left stereo = sum + difference
Right stereo = sum - difference
Mono = Left stereo + Right stereo

Which is easiest? In your supposedly simpler method, you have to
first
extract the mono signal anyway before you can even reconstruct
the
stereo channels, so it isn't rocket science to see that your
method is
far more complex.

In the context of a stereo-capable radio with mono speaker and
stereo
outputs, the recombination method is more straightforward.




It may be done at
line level (ie. before the audio feed reaches the amplifier), as
it is
in Bill's Roberts radio (thanks to Peter Watson for providing a
link to the
service manual), but it's still the same recombination technique.

I'm sure there are some others out there which don't use
recombination,
but there are plenty that do.

Congratulations are still in order for Steven though, because,
after
more than a year and three very long threads, he's finally managed
to learn
that "FM stereo hiss" isn't audible through a mono radio's speaker

I'm still very confused whether he agrees with this or not!


You patronisingly twat! Do you seriously believe that there's anything
that you understand that I don't? You're deluding yourself if you do.


Er, if you recall, the discussion of this began when I had
reviewed a
Roberts DAB/FM portable radio which did have hiss present on the
mono
speaker because it had incorrectly been set to stereo mode by
default.
I contacted Roberts saying that was a fault with this radio,
precisely
because "stereo hiss" should not be present on a mono speaker.

...and the *reason* you concluded that the hiss shouldn't be there
was
because the radio was set to Stereo but *if* Mono was derived for
the
speaker either by combining L&R *or* using the Mono output of the FM
stage then the mode *shouldn't* have made any difference!

The conclusion therefore is that the receiver was faulty (you got
that
bit right) because the derivation of Mono didn't work correctly,
*not
because the receiver was set to Stereo*...


Oh, have you got the circuit diagram for the Roberts radio I reviewed
as well then? Out of interest, how did you manage to figure out which
Roberts radio I reviewed when I haven't mentioned it? Do you have
supernatural powers there, Petey? And out of interest, how do you know
that there wasn't a software bug in the software-defined radio FM
receiver implementation, when, IIRC, theory shows that it's impossible
to prove that no bugs exist in a piece of software?

Anyway, Peter, this is a NG about digital radio - with discussion
slanted towards the technology side of things - but I don't think I've
ever seen you post anything about digital radio technologies yet. Is
this because digital radio technologies are too difficult for someone
like yourself to understand, Peter?



--
Steve - www.savefm.org - stop the BBC bullies switching off FM

www.digitalradiotech.co.uk - digital radio news & info

"It is the sheer volume of online audio content available via
internet-connected devices which terrifies the UK radio industry. I
believe that broadband-delivered radio will explode in the years to
come, offering very local, unregulated content, as well as opening a
window to the radio stations of the world." - from the Myers Report


.

Relevant Pages

  • Re: "Listeners dont want DAB"
    ... "Stereo FM tuner set to FM mono mode: ... that it's a good idea to add the Left and Right channels together ... were adding two identical signals together, ...
    (alt.radio.digital)
  • Re: Roberts Gemini 49
    ... zero-mean random noise signals. ... world* on the Mono FM component and the noise Stereo DSBSC component ...
    (alt.radio.digital)
  • Re: Roberts Gemini 49
    ... In the end all the theory and maths in the ... the stereo noise gets cancelled out. ... The signals that are used to reconstruct the Left and Right stereo ... Invented FM Mono System That Doesn't Exist, er, doesn't exist, so I ...
    (alt.radio.digital)
  • Re: FM radio limitations (?)
    ... > ...the stereo subcarrier sops up deviation very nicely think you. ... > A Stereo transmission tends to sound noisier that a Mono signal. ... As the noise in the 23 KHz ... as MPX signals have more bandwidth than a Mono ...
    (rec.audio.pro)
  • Multiplex decoder nearly rewired.
    ... The L&R signals are taken to switch contacts to select stereo or mono. ...
    (rec.audio.tubes)