I have a question about the extent to which the DAB stereo image can be
sacrified in order to reduce the sound distortion.

If I simply add the two analgue channels together (after decoding) to
give a monaural sigal would this reduce the distortion or would I need
something more elaborate and 'digital' to achieve it? Perhaps the
answer is different for "true stereo" channels, such as Radio 3, and
the more numerous "joint stereo" channels.

A related question is: Would Radio 3 give less distortion if it used
joint stereo instead of 'full' stereo? That is, could the BBC choose
to reduce distortion at the cost of a poorer stero image?

thank you to anyone who cares to respond,

Robert

In article .com,
Robert
wrote:
I have a question about the extent to which the DAB stereo image can be
sacrified in order to reduce the sound distortion.

If I simply add the two analgue channels together (after decoding) to
give a monaural sigal would this reduce the distortion or would I need
something more elaborate and 'digital' to achieve it? Perhaps the
answer is different for "true stereo" channels, such as Radio 3, and the
more numerous "joint stereo" channels.

I am not sure, but for 'real' stereo as distinct from 'joint' I suspect
you'd find that there will be no tendency for the distortions to be mainly
aligned in the L-R direction. Hence I doubt that simply paralleling for
mono would reduce the distortion.

With 'joint' I suspect it would just lower the level when the joint part
was full L or R, and not alter the distortion.

A related question is: Would Radio 3 give less distortion if it used
joint stereo instead of 'full' stereo? That is, could the BBC choose
to reduce distortion at the cost of a poorer stero image?

No idea.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

Robert wrote:
I have a question about the extent to which the DAB stereo image can
be sacrified in order to reduce the sound distortion.

If I simply add the two analgue channels together (after decoding) to
give a monaural sigal would this reduce the distortion or would I need
something more elaborate and 'digital' to achieve it?


It wouldn't improve anything, I'm afraid. The problem is that the bit
rate is too low and it provides a poor representation of the signal
(even with imperceptible frequencies removed), so adding the left and
right channels doesn't remove the fact that both channels are poor
representations of the respective channels. Radio 3 at 192kbps is too
low to match FM, let alone the 128kbps stations.


Perhaps the
answer is different for "true stereo" channels, such as Radio 3, and
the more numerous "joint stereo" channels.

A related question is: Would Radio 3 give less distortion if it used
joint stereo instead of 'full' stereo? That is, could the BBC choose
to reduce distortion at the cost of a poorer stero image?


Yes. When higher bit rates like 192kbps are used the encoder can choose
on a frame-by-frame basis whether to use joint stereo or not depending
on the signal characteristics. At 128kbps joint stereo is necessary on
all audio frames (unless there's no difference between the left and
right channels) because the bit rate is insufficient to provide
reasonable quality.



--
Steve - www.digitalradiotech.co.uk - Digital Radio News & Info

Please sign the petition asking the BBC to provide better audio quality
on its radio stations on DAB, Freeview, satellite and cable:
http://tinyurl.com/a68e4

"
If I simply add the two analgue channels together (after decoding) to
give a monaural signal would this reduce the distortion or would I need
something more elaborate and 'digital' to achieve it?

It wouldn't improve anything, I'm afraid. The problem is that the bit
rate is too low and it provides a poor representation of the signal
(even with imperceptible frequencies removed), so adding the left and
right channels doesn't remove the fact that both channels are poor
representations of the respective channels.
"

That's a pity. On FM with poor reception one can reduce noise by
taking out the stereo decoder. On NICAM (TV) sound on channel 5 (via
analogue transmission) I find I can reduce the distortion by switching
the TV to mono (why is channel 5 so much more distorted than the
others?). I had hoped that DAB might allow something similar. I
guess that if the distortion is uncorrelated between the two channels I
might reduce it by root(2) by adding the L and R channels. That would
give a 3dB reduction perhaps.

"Radio 3 at 192kbps is too low to match FM, let alone the 128kbps
stations. "

I listen mainly to Radio 3 and subjectively I do find it pretty much as
good as FM. I don't mind accepting a very small amount of distortion
in order to remove the background hiss; I am not able to put up
external aerials. Classic, however, is noticeably worse than FM and
things like the World Servcie are very distorted indeed (and in mono).
What a pity we in the UK have ended up as the 'poor man of Europe' with
regard to DAB sound quality.

Robert

I know this is off (my own) topic but: would the sound quality be
better if I picked up BBC radio from the Astra satellite instead of
DAB?

I think people have also suggested using the digital TV box but said
that the data rates were going to be reduced, or had already been to
match that of DAB, possibly in order to avoid negtive comparisons.

Robert

Robert wrote:
I know this is off (my own) topic but: would the sound quality be
better if I picked up BBC radio from the Astra satellite instead of
DAB?


Yes, the quality is better via satellite because all the BBC stations
apart from Radio 3 use higher bit rates on satellite, and Radio 3's bit
rate is reduced on DAB in the daytime whenever Radio 5 Sports Extra is
on air, which is every Saturday, and quite a lot during the summer, e.g.
cricket, tennis.


I think people have also suggested using the digital TV box but said
that the data rates were going to be reduced,


I've never seen any bit rates been reduced on satellite, so I don't know
where they get that from.


or had already been to
match that of DAB, possibly in order to avoid negtive comparisons.


Nope. If anything the bit rates on the BBC stations on satellite will go
up in future.


--
Steve - www.digitalradiotech.co.uk - Digital Radio News & Info

Please sign the petition asking the BBC to provide better audio quality
on its radio stations on DAB, Freeview, satellite and cable:
http://tinyurl.com/a68e4

In article .com,
Robert wrote:
That's a pity. On FM with poor reception one can reduce noise by
taking out the stereo decoder. On NICAM (TV) sound on channel 5 (via
analogue transmission) I find I can reduce the distortion by switching
the TV to mono (why is channel 5 so much more distorted than the
others?).

Sounds like you have a faulty NICAM decoder. I've got a Panasonic TV which
does just this - the NICAM is distorted on peaks while the FM is clean.
But none of the several other NICAM devices on the same aerial exhibit
this effect.

--
*Is it true that cannibals don't eat clowns because they taste funny?

Dave Plowman London SW
To e-mail, change noise into sound.

Dave, I wondered if the decoder was faulty, but I have observed the
same effect on three different TV/videos so I concluded that it was the
transmission rather than the receiver, also it only does this on
channel 5. I'm in Cambridge.

Robert

In article .com,
Robert writes

Dave, I wondered if the decoder was faulty, but I have observed the
same effect on three different TV/videos so I concluded that it was the
transmission rather than the receiver, also it only does this on
channel 5. I'm in Cambridge.

Robert


Seems like its out of tolerance. Give Arquiva a mail their based up at
Emley Moor maintenance for this region IIRC!....
--
Tony Sayer

In article , Dave Plowman (News)
wrote:
In article .com,
Robert wrote:
That's a pity. On FM with poor reception one can reduce noise by
taking out the stereo decoder. On NICAM (TV) sound on channel 5 (via
analogue transmission) I find I can reduce the distortion by
switching the TV to mono (why is channel 5 so much more distorted than
the others?).

From what I have been told (by someone at the BBC) the 'mono' sound on
broadcasts is derived from the NICAM sent to the transmitters. So unless it
happens to be difference mode, any distortion on the NICAM would presumanly
also turn up on the mono sound as well.

Sounds like you have a faulty NICAM decoder. I've got a Panasonic TV
which does just this - the NICAM is distorted on peaks while the FM is
clean. But none of the several other NICAM devices on the same aerial
exhibit this effect.

I also have a Panasonic TV. If I use its 'analog' (Pair of line phonos)
outputs it gives audible distortion from loud sounds from receiving NICAM.
However sounds fed in via scart also give distortion when taken out again
via the phonos. Hence I assume it may not be the decoder as such, but poor
circuits later in the TV sound system. (The TV's speakers also produce
levels of random noise you can easily hear if you put your ear near them
with the TV volume wound down to zero. Sign of a poor power amp system as
well.)

I like the picture the TV gives, so use it as a display. The sound system
seems to me to be on a par with the kind of performance which audio systems
left behind them decades ago. Hence I simply bypass the TV system whenever
watching DTTV or DVDs.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html