Xm Satellite Radio

Entertainment. We've all got to have it, especially in our cars. We've seen an explosion in the last 3-5 years of audio entertainment products, from portable MP3 players with a fixed amount of storage, to car audio head-units that can play CD-Rs and read mp3s to mobile DVD players. DirecTV, the famous television satellite broadcaster, roared onto the home entertainment scene in the mid 1990s, and has been a successful player in this ever changing and competitive market.

But aside from the MP3 Revolution, audio entertainment has not changed much in the last 40 years. In your car, or on your home stereo, you've got two options: Listen to commercial FM/AM programming, or play music from some medium, 8 tracks, audio cassettes, CDs, or recently, hard drives. Whereas television has exploded with hundreds of cable and satellite channels, audio entertainment has remained quite stale, and indeed, in many people's minds, gotten worse in the last decade.

Enter Satellite Radio. The marketing hype tells us it is different, fresh, new, and commercial free. It offers greater choice and better quality, a more diverse set of music, talk, sports, and entertainment. And you won't ever have to worry about being out of range of this quality programming, because it's nationwide.

But does satellite radio deliver on these promises? I bought into this 'revolution' early, having purchased an XM Satellite Radio (one of two competitors) in mid March. I've been testing and evaluating not only the unit, but also the content XM Radio provides. Read on if you'd like to seriously explore some alternatives to your current audio entertainment paradigm.

Satellite radio concept, implementation/technology

Concept

The idea behind satellite radio is quite basic. For all intents and purposes, you can think of Satellite audio's model as a direct copy of Satellite television. XM Satellite Radio and Sirius Radio both have looked at DirecTV's success and thought about how to attract that type of market to its product. The idea is that people who were initially attracted to DirecTV because of its quality, depth of programming, and cost will also be willing to pay monthly for access to satellite audio. Like satellite television, Satellite radio is not marketed to any one demographic more than any other. In the US market, there's two players: XM Satellite Radio and Sirius Satellite Radio. XM and Sirius both know that one can find literally hundreds of DirecTV receiver dishes on many expensive houses, lower income apartment buildings, and even office buildings, and they are hoping to spread in the same way.

But Radio is free, you say, why should I pay for it? Well, XM and Sirius have also thought about that same question, and have come to the conclusion that while a person can still get free television over UHF and VHF antennas, the vast majority (almost 80%) of Americans pay money monthly to subscribe to cable or satellite TV.

To that end, both XM and Sirius have developed content that would satisfy just about any audio listener, casual or hardcore. Likewise, they both, for the time being, have low monthly costs ($9.95/month for XM, $12.95/month for Sirius), and are offering many incentives such as free installation and rebates on the hardware as well as a few months of free service in cooperation with major retailers such as Best Buy. XM and Sirius also have a distinct advantage DirecTV did not have; they can both market their technology and product to major auto manufacturers. Indeed, Cadillac is including XM enabled receivers in their high-end cars starting next year, and a buyer can even roll the monthly XM charge into his auto loan.

Implementation/Technology

XM has a 100,000 Sq. Ft. broadcasting facility in Washington DC as well as some satellite offices in New York. Sirius broadcasts out of New York City. They both require a person to buy equipment ranging from $200 to $500 in order to receive the signal, and they both have similar methods for dealing with spots not conducive to satellite coverage.

I will take you on a tour of a single song, as it travels off a CD Rom or Hard Disk at XM's Broadcast facilities, gets diced and sliced in an encoder, combined in a multi-plexer, gets bounced up onto the satellite, and back down to your receiver, where it is decoded with header information, and finally, put back into analog so your primitive human ears can enjoy it.

Some of this will be supposition, as XM and Sirius both use different encoders (XM uses CT-aacPlus while Sirius uses PAC), frequencies and technology, and are not exactly forthcoming about the exact methods. However, satellite radio broadcasting has a number of standard conventions, and the only way in which XM and Sirius differ from traditional broadcasters is on the receiving end, which I will talk about in depth.

A song at XM Radio starts its broadcast life by being recorded into a specific format on some storage medium. It probably is encoded at a high rate (384kb/s) so as to preserve quality while being somewhat efficient with drive space requirements. It is cataloged and organized in a similar way that we use ID3 tags for our MP3s. The DJ (already an out-dated term, he probably never touches a disk) then selects the track or album of tracks to play for the next 15 to 30 minutes. The DJ previews the music, much like you listen to an MP3, by simply letting the control system decode the original stored file. After the next 15-30 minutes of audio is decided, the song moves off to yet another encoder.

Now it's important to understand the encoding process. Each format, or in XM's case, channel, is handled by an encoder. For example, XM Channel 4, the 40s Music channel, goes through the process above, and is sent to its own encoder (Analog to Digital), where it is digitized in real time into 1's and 0's. The audio wave is simply sliced into segments that equate a value of 0's or 1's depending on the amplitude and frequency of the wave. Whereas commercial broadcasters like Clear Channel may encode at this point at up to 256kb/s, 48KhZ (Producer rate), XM most likely encodes up to 128kb/s, 44.1Kh (CD Quality) for reasons I will state later. Keep in mind that this is not the broadcast rate.

A sample picture of the A to D converters XM would use. Each XM Channel

would have a primary and backup encoder for real-time A to D encoding. That's 200 encoders!

Encoded, our 40s swing song now travels to a multiplexer, where it is combined with the 80s channel, the Classical Opera channel, Fox Sports