I'm still trying to decipher how iTunes Match "works".
As I understand it, they use some kind of "fingerprinting" technology to identify the song. Think of a cryptographic digest like MD5 or SHA-1, but designed for audio. They generate a fingerprint for every track you didn't purchase from the iTunes store. Then they upload the list of fingerprints to an Apple server, which compares them against tracks in Apple's servers.
If a song's fingerprint matches a song on Apple's server, then the file on the Apple server is available to download to other devices. If no match is found, then your file is uploaded (with high bit-rate files being transcoded to 256K AAC), allowing your devices to download the song itself.
Conceptually, this isn't anything novel. In practice, it's a big deal. An algorithm to accurately fingerprint songs that is also fuzzy enough to deal with rips from different CDs and songs digitized from vinyl and cassette (which often works, but not as reliably as rips from CD) isn't easy to develop, and requires a level of CPU power that wasn't easily available a few years ago.
I wonder what algorithm they actually are using. I suppose a trivial method might be to just transcode the song down to something extremely small, like a 1Kbps representation. At that bit rate, a song is about 7.5K bytes per minute of music. This would be easy to upload and compare against a database of similarly-transcoded files. The result would sound terrible, but it would still contain more than enough data to clearly recognize and identify the song.
why would i want to pay money to listen to music i already own. alrighty then.
Good question. You're not paying to hear your music. You're paying to serve it to your portable devices via Apple's servers. $25 sounds like a good deal for this kind of service, even if nothing went to the record labels.
IMO, this is a win-win situation. You get a fairly cheap hosting/streaming solution for your music, and the record labels get extra revenue that they wouldn't otherwise have gotten.
Radio isn't free. You, the listener, don't pay, but the radio stations pay the labels for broadcast rights.
I still don't see the point in iTunes match. If you've got songs ripped from a CD they must be on your Mac/PC, so just sync your iPad, iPhone and iPod touch once, and the music will be on all devices. Then continue to use the iTunes store.
True. And if this is what you want to do (it's what I want to do), there's nobody stopping you.
If, on the other hand, you've got a lot of music, and it won't all fit on your portable devices, then this kind of service is valuable.
For example, I've got about 10,000 songs consuming 50GB on my hard drive. I have them all synced to an iPod classic with no problem, but they wouldn't come close to fitting on an iPhone or an iPad (unless I get the most expensive model and want to use nearly all of its capacity for music.)
Today, I use a system of smart playlists to sync a 3.5GB subset of music to smaller devices, like my 4GB iPod nano. With iTunes Match, an internet-connected device like an iPhone will see my entire collection, downloading tracks on an as-needed basis, allowing me the luxury of choosing what I want to hear when I'm away from my Mac.
Is that ability worth $25/yr? For some, it definitely is. Not for others.