How do they remaster CDs and DVDs?

What are the differences between remastering and mastering?

Consumers often buy remastered CDs or DVDs that feature classic movies or albums.
Consumers often buy remastered CDs or DVDs that feature classic movies or albums.
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Every record, CD and MP3 has to be mastered before it's distributed to the public. The master is the final, definitive version of each track that will be copied and printed on millions of CDs and downloaded from Web sites like iTunes. A master is created by a mastering engineer, a special breed of audio engineer who works in a dedicated mastering studio.

Mastering engineers are different than studio recording engineers. A recording engineer's job is to faithfully record every instrument and vocal track with as much clarity -- and as little signal processing -- as possible. In recording terminology, signal processing is any kind of compression, distortion or other effects that alter the sound of the recording.

Once the recording engineer has captured clean copies of every track, the music is handed over to a mixing engineer who is responsible for assembling the final mix. The mixing engineer takes each separate instrumental and vocal track -- perhaps dozens for a single song -- and tweaks their volume, stereo pan and other settings to achieve a balanced, satisfying whole. Even though this is called the final mix, nothing's final until it's passed through the hands of the mastering engineer.

A mastering session is called finishing, because this is where each song on a CD receives the final adjustments that make it sound great on vinyl, CD, MP3 or radio. Each different playback medium requires its own special equalizing, balancing and compression to make the music clear and powerful for the listener.

Vinyl records, for example, are usually played on home stereo systems with good speakers. MP3s, however, might be played on a pair of cheap computer speakers or through an iPod. It's the mastering engineer's job to know how to make the songs sound great wherever and however they're played. Mastering engineers usually have decades of experience in the recording business and an exquisitely trained ear.

Remastering is simply the process of taking an existing album and mastering it again. In the 1980s and 90s, many bands issued "digital remasters" of their original vinyl or tape cassette recordings. In this case, the albums were being remastered for playback on CDs. To do this, a mastering engineer would digitize the original analog version of the final mix and use a digital audio workstation (DAW) like Pro Tools to rebalance and equalize all of the tracks.

Remastering is usually reserved for box sets of a band's "greatest hits" or other special releases. The word has taken on a highly promotional significance, used to resell existing music to consumers with the promise of sharper sound clarity and even a totally new sound.

DVDs are remastered for many of the same reasons. The idea is to use modern digital editing technology to create the cleanest, most artistically authentic print of an existing movie. The editors go back to the original film stock and use special editing software to remove dust, fix damaged frames, improve color balance and greatly improve the clarity and quality of the audio.

These remastered DVDs are often reissued on high-definition discs with the director's originally intended aspect ratio (wide-screen, for example, instead of the 4:3 ratio favored by conventional TV screens) and with extras like behind-the-scenes documentaries and filmmaker interviews. Once again, remastering is an excellent way to breathe new life into an old product.

So what exactly are the tools and techniques that mastering engineers use to remaster CDs and DVDs? Find out in the next section.