Seeing as a post goes through here discussing something related to music downloading every few months, and most posts ask the same sort of questions, I thought I would create a quick reference.

What are some modern technologies incorporated in digital music?
Digital music is, quite obviously, digital. This means that a continuous sound waveform is broken up into discrete amplitudes:

Each amplitude is assigned a number, describing how "high" it is off the horizontal axis in the picture above. The number of discrete amplitudes is called the resolution, and a higher resolution will make the wave less "choppy", and your music sound better. "16-bit" is a common resolution. Remembering that a bit is a "binary digit" - ie a 0 or 1, this equates to 2¹⁶ = 65536 different amplitudes.
The frequency of sampling also affects how your music sounds. If your sound wave changes suddenly (ie has high frequency components), you won't hear this unless you sample fast enough:

CD audio is sampled at 44100 Hz - ie 44100 times per second. You might imagine that storing all this information without compressing it would take a lot of memory - which is exactly what CDs do! CDs store all the digitised music uncompressed, which is why they play about an hour's music and require 700 Mb to do so.

A variety of ways of compressing music have been invented, using little tricks to cut out parts that we won't notice if they go missing. MP3, AAC, WMA, and OGG are all popular formats that have become better over the years, though some do better jobs than others of accurately reproducing certain sounds such as the high frequencies generated by cymbals. Listening to compressed music all the time can deaden your ability to perceive the difference between compressed and full fidelity recordings. Recording equipment, acoustic environment, the number of channels, your amplifier and your speakers all contribute to the quality of the sound. And, if you own any Paris Hilton songs, so too does your taste also contribute to the sound quality, in a different sense.

All file formats are proprietary except OGG, which means you must pay royalties to the owners of the intellectual property if you want to write software that uses them. A codec is a program that compresses and decompresses the music in the way you want.

What are some of the different ways of obtaining digital music?
There are several:

• Copying friends' files (see "What is digital rights management"): This is where you simply copy their files, like you would make a copy of a CD. Because this is so obvious and easy, certain technologies have been incorporated into some file formats so that they will only work for whoever bought them originally.


• Online stores (also known as shops, depending on your location): Some stores offer "pay per download" services, such as iTunes, where you pay per song. Others offer subscription services, where you can download a certain quota of songs per month in return for a fee. Sometimes, you may choose your file format. Other times, you will only be offered one file format, especially if the store also manufactures music players designed to read this format.


• File sharing networks: This is the same as copying someone else's files, except instead of physically being present at their computer with an external drive attached, the files are copied to your computer over the internet. Programs like this index what files you have on your machine, and whether you want other people to be able to copy them. This way, other people can search to see what files you have on your computer, and vici versa. Programs like this include torrent clients and gnutella clients, such as BitTorrent, KTorrent, Limewire, Frostwire, and Napster.
  


• Buying and encoding the CD: This is where you buy the uncompressed version of the song on a CD, and turn it into an aac/mp3/wma/ogg file yourself. Many music player programs can do this for you.
  


• Extract it from the youtube video: A video is made up of images and sound. It's possible to separate the two, which is what this method does. Generally, to save a bit of bandwidth, youtube resamples the audio track and the resulting quality is lower than normal.

So how do I tell if my method of obtaining digital music is legal?
Easy - if whoever owns the rights to the music permits it to be downloaded that way! In practice, record companies own the rights to the music, and charge money for copies. Your use (eg personal listening or film soundtrack) determines how much it costs. So, the bottom line is this: If you download popular music that belongs to a record company and you didn't pay for it, your music is illegal.

It is important to understand that this distinction, so let's clarify for an example:

Jane loves listening to Alicia Keys, and when "No One" was released, Jane wanted to load it on her portable music player. Jane was broke at the time, and online stores wanted $2 for the song, but searching the internet, Jane found a program called "Lemonwire" whose webpage promised that she could share No One and lots of other songs. In the "FAQ" section, the webpage said that Lemonwire was 100% legal, and so Jane downloaded the program, searched for the song, and downloaded it in mp3 format. She downloaded 4 different files called "No One" before she found a working copy.

Some issues:

• Lemonwire said it was legal. This was true. Moreover, filesharing is also legal - it is not illegal to share files as long as the copyright holder consents. However, filesharing copyrighted files is illegal. In this case, Sony BMG Music Entertainment owns the copyright to No One, and has absolutely not consented for it to be shared without paying them royalties.


• Jane had to download 4 different files to get a working one. The first file was a file "No One.zip", which turned out to be an advertisement for an online poker webpage when extracted. The second file was "No One.mp3", but would not work, for some reason. The third was "No One.mp3", which had 15 seconds of the song, followed by random noise. In this case, Sony BMG was aware that people were downloading the file this way, and to discourage them, they distributed bogus copies on the network.

Use your common sense
Popular music isn't free. It is almost entirely owned by record companies, and unless they are getting paid when you download, you are downloading illegally. It's pretty obvious how this system works.


What is digital rights management (DRM)?
DRM is a way of describing the technologies that control your access rights to files. As it applies to music, DRM can:

• Limit the number of (working) copies you can make of the file


• Limit which users may play the file


• Limit which devices the file can be transferred to


• Limit the number of times the file may be played

...and a whole lot more. You won't be surprised to know that many users of digital music prefer their music to be DRM free.

How do people get viruses from filesharing networks?
AKA "I heard that Limewire/Frostwire/whatever doesn't give you viruses". Wrong, and misguided. Most of these programs connect to the same network of computers, they just behave in slightly different ways. Some look different, some search more efficiently ... but they all access the same files on other people's computers. These files are prospectively virus-infected. Some examples:

• A music file with an embedded portion in it to take advantage of a buffer overflow in a certain popular music player. This causes the player to malfunction, and execute the rest of the file with administrator privileges, installing, say, a virus.


• A file meant to look like a music file, but is actually a program that allows someone else to connect to your computer via the internet (a "trojan horse"). After connecting, the attacker can do several things, including: (1) install a program on your computer that logs everything you type, and steals your bank/facebook/email passwords, or (2) install a program on your computer that sends out spam email to thousands of addresses. Both of these attacks are very popular, and a few DDN members have similar experiences.


• A file meant to look like a music file, but is actually a program that installs a virus on your machine. The good old fashioned way.

When you download a file from a filesharing network and play/execute it, you are trusting that it is a legitimate file, and that if it isn't, your spyware/antivirus/music player won't let it harm your computer. So remember: whateverwire isn't giving you virusess - you're downloading them and installing them of your own accord.

How do people get caught using filesharing networks?
It's pretty easy. I search, and find music on your computer over the filesharing network. You are thus distributing illegal copies of the songs. Alternatively, I monitor your internet usage (It's not that hard, and many countries are now forcing ISPs to do this). I know your IP address. I ask your ISP where you live in the form of a subpoena, and then mail you a letter requiring you to pay a fine or go to prison.

Right, I'm aware of the risks, how do I do (insert something illegal here)?
It's obviously not responsible, nor ethical, to detail how to steal music. The value, ease (if you're a little technologically inclined), and low probability of getting caught have made this common practice. Facing facts, with a little brains, you'll be able to pull it off and not get caught. Don't expect others to be forthcoming in providing the necessary brains around here, though.

Good thread