THE LATEST IN NETWORKING AND WIRELESS TECHNOLOGIES
■ BY LOUIS E. FRENZEL W5LEF
WI-FI MAKES INTERNET
One more option for the radio enthusiast
You just don’t know how lucky you are. Just think of all the options you have in
listening to radio. There are the old standbys like AM and FM stations that most
of us still listen to mainly in the car. There are thousands of stations nationwide
and dozens in your local area. Then there is the newer HD radio that puts
digital broadcasts into the AM and FM bands for higher fidelity, better noise, and
fading immunity, and more station choices. With well over one thousand
stations nationwide, you probably have several HD stations locally.
Satellite radio is another form of
digital radio. With either Sirius or
XM satellite radio, you have almost
200 stations each to choose from.
And don’t forget shortwave radio.
Most of you don’t listen to this
but there are hundreds of English
language stations worldwide. Then,
of course, you have Internet radio.
WELCOME TO INTERNET
Internet radio is really a misnomer. It isn’t really radio as such
meaning receiving signals wirelessly
as in all the other forms of radio.
Instead, Internet “radio” is getting
audio broadcasts via the Internet.
You listen to talk, news, and music
on your PC or laptop via the
browser and sound capabilities.
If you have never tried it, you need
to experiment. It opens up a whole
new world of listening possibilities.
There is something for everyone,
even wild stuff the FCC doesn’t allow
over the air waves.
The audio to be broadcast is
digitized in an analog-to-digital
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converter (ADC) then put through an
audio compression process. The
resulting compressed digital data is
then serialized and sent out over the
Internet via TCP and UDP packets.
We call this streaming audio. These
audio packets pass through one or
more servers or routers before hitting
your PC. There is a lag or delay as
this happens but you don’t really
notice it unless a particular server or
router gets overly busy; you will hear
jerky spaced out chunks of audio.
The audio is compressed to
reduce the number of bits to be
transmitted. If you want to transmit
hi-fi audio with CD quality, that means
you need to cover up to 20 kHz
signals. This requires sampling the
audio in the ADC at least twice that
(or 40 kHz). The digitizing rate in a
CD is 44.1 kHz. Let’s say we have a
16-bit ADC that samples at this rate.
That means we are transmitting 16
serial bits for each sample. That
translates into 16 x 44.1 kHz = 705.6
kHz or 705.6 kilo bits per second
(kbps). If you are transmitting two
channels for stereo, the data rate
goes up by a factor of two or 1.4112
Mbps. You need a high speed
Internet connection like cable or DSL
to hear this. The answer to this
problem is to compress the audio.
You digitize the audio as just
described and store it in a memory.
Then you subject that audio data t
o a compression algorithm that
effectively reduces the number of bits
and words that need to be transmitted. The data rate can be much lower.
Examples of digital audio
compression algorithms are the
familiar MP3 and Apple’s iPod AAC
standard. There are many others like
Windows media files or RealAudio.
And keep in mind when you are
storing digital audio on a disk or in a
Flash memory inside an MP3 player
or iPod, the compression technique
greatly reduces the number of bits
and words you need to store, and
therefore the size and cost of the
memory. To listen to Internet radio,
all you do is go to your PC and open
the browser and search for Internet
radio stations. Many of the available
stations are just your local stations
streamed to the Internet. You can
listen to them on the PC — no radio
needed — and you can do that from
any place in the world that has an