Internet Radio
Internet radio seems to have
earned itself a reputation for being at low audio quality, which in a
lot of cases has been a fair criticism up to now due to the bigger stations
typically using very low bit rate levels until recently. However, the
Internet will become the system that provides the highest audio quality out of
all of the digital systems that carry radio within the next year or two (as
of 2007)!
There are literally thousands of Internet radio streams available on
Internet radio portals, such as shoutcast.com,
which use bit rate levels of 128 kbps or higher using MP3, and some of
these Internet stations actually have very good audio quality.
More significantly though, is the fact that the big traditional radio
stations that broadcast on FM have started to provide higher bit rate
streams, and the audio quality of these streams are far better than the
quality of the Internet radio streams we used to get. The biggest change
in terms of UK stations has been GCap Media, the UK's largest commercial
radio group, launching 128 kbps WMA streams for all or almost all of the
stations it owns -- links for these streams are given in the tables
below.
There are also major developments on the horizon regarding the
technologies used to distribute Internet radio streams. Until now,
Internet radio streams have been 'unicast', which means that the
Internet server sends one stream per listener, but later this year (as
of August 2007), the BBC will be launching 'multicast' streams for all
of its national stations. With multicast, the broadcaster only has to
send one stream of each of its stations to each ISP, and the ISPs then
forwards the streams to anyone on their networks that want to listen to
the stations. Multicast therefore vastly reduces the amount of bandwidth
-- and therefore the cost -- that the broadcasters need to provide their
radio stations, and this will allow the broadcasters to provide their
radio stations at broadband bit rate levels, so the audio quality will
be very good. For example, the BBC's multicast radio streams are all
using 128 kbps AAC, which is the same bit rate and audio codec that
songs sold on iTunes use, and the audio quality that 128 kbps AAC
provides is far higher than that provided on DAB. Most of the other UK
commercial radio groups have also participated in the BBC's multicast
trial, so they are expected to provide their radio stations via
multicast as well within the next year or so.
Modern audio & video codecs
One disadvantage of "traditional" digital broadcasting
systems is that they're stuck with the same audio codec for many years —
for example, the biggest problem with the old DAB system is that it uses
the outdated and inefficient MP2 audio codec, and although DAB is now
adopting the AAC+ audio codec, the change to AAC+ will render all DAB
receivers that can't receive AAC+ (which at the time of writing is all
of them) partially obsolete in that they won't be able to receive any of
the new AAC+ stations that will launch over the next few years, and
eventually all of these radios will be rendered completely obsolete. Internet
radio solves this problem, because broadcasters can use any formats that
are supported by the main media players, such as Winamp, Windows Media
Player etc.
Multicast streams
Up to now, live Internet streams for radio stations have been
distributed using 'unicast', which means that each user that wants to
listen to a radio station is provided with their own individual
stream. Multicast goes about distributing live radio -- or TV --
streams in a far more efficient manner by only sending a single stream
of each channel to each ISP that supports multicast, and the ISPs then forward the
streams to any of their customers that want to listen to them.
So instead of the broadcaster needing to have enough Internet
bandwidth to provide tens of thousands of unicast streams in parallel
they only need to send one stream of each channel to each
participating ISP, which vastly reduces their Internet bandwidth
requirements -- the bandwidth saving for the broadcaster is around
99-100% for a channel with a high number of listeners.
Because the broadcasters save so much bandwidth, this allows them
to use higher bit rates for the streams, and so the audio quality is
higher.
The downside with multicast at the moment is that only a small
number of ISPs currently support it (see below for the list of ISPs
that do support it), so it won't become mainstream until the bigger
ISPs decide to support it. Virgin Media, which is one of the UK's
biggest ISPs is working on supporting it, though, so Virgin supporting
it would be a big step forward for the multicast service. According to
the BBC, if you want your ISP to support multicast then you should
contact them and ask them to support it.
BBC iPlayer
P2P
HDTV on multicasting
BT's 21CN
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