Okay....right.... thanks everyone for your interesting comments on the
merits/demerits of DAB (which I still don't like the 'sound' of).
However, does anyone have any information that pertains to my original
query, about the Radio 3 broadcast chain, and specifically what CD
players/DACS do they use and is there any compression?
Can we leave DAB for another thread please?
Thanks.
Well I'm afraid that DAB does come into it, well digital that is and
this is important.
As to the CD players the BBC actually use I believe they might use the
Denon broadcast series, can't remember the actual model number but they
won't have been chosen for audiophile considerations nothing in
broadcast ever is. Operation and functional is a far greater
consideration. Quality is just assumed that it will be OK.
A lot of material these days exists on hard disk playout which is simply
a computer and soundcard, albeit a good one (such as a digigram) with
some specialist scheduling software such as ENCO or RAS or the BBC have
a new German version, so almost all of the audio is digital in one way
or the other.
Where the problems lie is what bitrate that audio is at. In order to
save on disk space MPEG coding is used with bitrates as low as 96
sometimes 256K, but usually around 192. But I believe that Radio 3 uses
linear coding much the same as CD rates. Certainly Radio 1 is now using
linear PCM coding.
However as we know MPEG means that we can throw some info away without
it affecting the final sound too much, and should only be used in the
final path to the listener where the degradation is deemed to be more
"acceptable"
In audio another consideration is audio processing which is multiband
compression so as to normally make the sound louder and reduce the
dynamic range which is a necessary evil as during the day a lot of
people will be listening under less than ideal conditions so some
processing is considered "acceptable" however some stations back this
off at night when listeners will usually be using better systems.
However stations like classic FM are processed far higher than what
Radio 3 is. Have a look at,
www.orban.com and
http://www.omniaaudio.com for some examples.
Outside broadcasts will inevitably be sent over a digital path these
days but providing the system is linear coded, or at a high MPEG bitrate
then it shouldn't suffer too much. Sometimes dual rate ISDN is used at
128 K but better coders such as ACC are around. Sometimes satellite
links are used.
As to the final reception the signals are coded at BH and sent to the
transmitters over fibre links to the transmitter sites. DAB is
transmitted at what is now for DAB radio the high rate of 192 K/bits
which is the same as satellite and DTV though sometimes joint stereo at
160 K is used, some other broadcasters use as high as 256 K!. The UK
norm is 128 for a lot of other stations or even MONO as is the case for
radio 4 on DAB.
As to FM this is distributed as NICAM (several sites cover this on da
web) which is a high rate coding system this is converted back to
analogue to modulate the FM carrier at the transmitter. Some
transmitters such as the Harris Digit CD actually have a digital input
at linear coded rate which use a numerically controlled oscillator to
actually generate the FM carrier.
Have a look at
http://www.broadcast.harris.com/prod...tfolio/product
_details.asp?sku=WWWDIGFMEXCITE and download the spec sheet where you'll
see its rather impressive, however only a few live in the UK!.
So in the end you're listing to a digital signal source whether you like
it or not.
So either you get a satellite receiver and use that where the audio is
at 192 K and use an external DAC as the inbuilt one wont be that much
cop, I believe some Sony and Nokia units have digital outputs. Or a
terrestrial TV DTV box where Radio 3 is at 192 also. Same considerations
re the digital and inbuilt analogue outputs.
As for FM a good tuner and one of the better ones is the humble Denon
TU260 MK2 which at less than 100 quid from some outlets is an excellent
source, but do add a few bob for a good external aerial even if it
appears to work with the bit of wire type aerial supplied. Other tuners
exist but some of the older ones have excellent characteristics.
So what's the best for me after extensive listening tests?, none are
perfect its a case of you takes your coloration!. I reckon that FM still
haves the edge for radio Three which in the UK is about the best audio
quality source on radio, and DAB and DTV sources come second. The DAB
sound is sometimes metallic in nature with a sorta buzz on some sources.
Course if the signal was at a high bitrate or linear coded on satellite
then I'd just junk the FM tomorrow and use that. FWIW also digital
distribution is a better option than analogue if you heard what used to
end up in places distant to London which were fed over post office
landlines the difference was very marked indeed, and the digital system
which was referred to as Pulse Code Modulation was developed by the BBC
in order to overcome the limitations of the analogue lines available at
the time.
Like some things the original intention was in the best interests of the
sound and engineering, but unfortunately these days digital in some
circles means a sodded up sound caused by such things as digital
transmission and storage limitations, but that's another few pages which
you can find over on alt.radio.digital!...
--
Tony Sayer
BBC Radio 3
Linear Mode
