How do they remaster CDs and DVDs?

By: Dave Roos
Independent filmmakers like Spike Lee often release new remastered versions of their films.
© Elisabetta A. Valla/WireImage/Getty Images

Digital technology has not only allowed filmmakers and musicians to create inspiring new works of art, but it's also given audio engineers and film editors the chance to reach back and restore classic albums and movies to their original grandeur.

Remastered CDs and DVDs promise consumers a crystal clear, artistically faithful reproduction of their favorite music and films. Led Zeppelin fans rush to the record store every time the band issues another "definitive" remastered collection of its pioneering rock albums of the 1960s and 70s. And companies like the Criterion Collection have created a market for painstakingly restored, high-definition DVD releases of classic, foreign and independent cinema from filmmakers like Jean-Luc Godard, Akira Kurosawa, and Spike Lee.


But all of this digital wizardry is not without its detractors. Many listeners complain that remastering CDs, especially in the age of the MP3, is nothing but an excuse to make the music louder and overproduced. DVD remastering runs into the same problems. There are viewers who feel that film restoration can go too far, taking away the imperfections of the filmed image that make it unique and alive.

What are the differences between mastering and remastering? What tools are used to remaster CDs and DVDs? What do consumers say about the finished product? Read on to find out more.


What are the differences between remastering and mastering?

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.


CD/DVD Remastering Process

Sound engineers often remaster old CDs.
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If you're remastering a vinyl album for playback on CD, then the first step is to locate the original analog version of the final mix and digitize each track into a DAW like Pro Tools. If you're remastering an existing CD, then you'll need a copy of the original digital version of the final mix.

The next step is to assemble the tracks in the desired order. Track order influences the overall flow of the CD, like the emotional highs and lows of a good mix tape. Mastering engineers worry about track order first, because it will affect how each song is sonically balanced with those that come before and after it.


Now the mastering engineer uses a palette of software tools to "sweeten" the sound of each song. It's important to understand that mastering engineers tweak and adjust the sound of the entire stereo mix of a song, not the settings of each individual instrumental or vocal track. Those individual track settings are already locked in by the mixing engineer.

The most common tools of the mastering engineer are a compressor, a limiter and an equalizer. Both compressors and limiters are used to control the loudness of the song. This is not the same as the volume of the song, which is ultimately controlled by the listener. To understand how compressors and limiters work, you first need to understand the difference between loudness and dynamics.

Dynamics refer to the overall dynamic range of a song, which is measured by calculating the difference between the loudest and quietest parts of a song. In the recording studio, loudness is measured in negative decibels (-dB) with zero representing the loudest recordable sound. Without compression, a song might have a loud section that registers at -6dB and a soft part that measures -48dB for a total dynamic range of 42dB.

If a mastering engineer wants to make the whole song louder, he might raise the gain by 6dB. But if he did that with our example, then the loudest part of the song (-6dB) would shoot up to zero, which is too loud to play back clearly on most stereo systems. Instead, he would use a compressor to shrink the dynamic range of the song, so that the loudest parts aren't so loud and quiet parts aren't so quiet. He can now safely raise the overall gain of the song without pushing the loudest parts into the red.

A limiter works in a similar way, putting a cap on the loudest parts of a song. If a sound exceeds that limit, it will be automatically reduced by a predetermined ratio, say 2:1. So for every two decibels over the limit, the sound will be reduced by one decibel. A good mastering engineer knows how to use compressors and limiters to add sufficient loudness and emotional impact to a track without over-flattening or collapsing the dynamic range.

Next, the engineer uses the equalizer tool to achieve the perfect tonal balance of the song. A software equalizer looks just like the analog equalizer on your home stereo with faders for each frequency of the audible spectrum. Throughout the song, the mastering engineer will adjust the faders to fatten bass sounds, highlight treble details and keep everything balanced.

For DVD remastering, film and video editors use special restoration software like MTI's Digital Restoration System (DRS) to painstakingly remove dust and debris from damaged film stock and restore colors to their original splendor. Special audio editors then use systems like ProTools to remove blips and beeps, boost dialogue levels, clarify audio effects and add Dolby 5.1 surround sound [source: Frucci]. Today, many DVDs are being specifically remastered for release on high-definition Blu-Ray DVDs.

Despite the transformative power of digital editing, some people are not fans of remastering CDs. Read on to find out why.


Complaints with Remastering CDs

Fans criticized Led Zeppelin's Jimmy Page for his remastering of their album, "Mothership."
© Jun Sato/WireImage/Getty Images

Stereo salesmen know the quickest way to sell a customer on a pair of high-end speakers: turn it up! Loud music packs an immediate emotional punch, and the same logic that's used to sell speakers -- the louder the better -- has been used by the recording industry for decades to sell records, tapes and CDs. Whether they like it or not, mastering engineers have been enlisted in what's known as the loudness war.

Here's how the loudness war works. If a record company releases a new single on the radio, the song needs to stand out from the pack. Record producers have figured out that the easiest way to inject a song with instant freshness and excitement is to make it louder than the songs that preceded it. Mastering engineers are constantly being urged by producers, artists and record company executives to make each album louder than the competition.


With the introduction of the MP3, the loudness war went into overdrive. MP3s are played back on flimsy computer speakers and through iPod ear buds, which lack the fullness of sound that's achieved on a hi-fi stereo system with good speakers. Sounds in the lowest and highest frequencies, for example, barely register on computer speakers. So if you're a record company and your goal is to sell MP3s, you need to make those MP3s pack a wallop. And how do you do that? Make the song even louder, of course.

The major complaint with the loudness war is that these tracks sacrifice sound quality for the sake of sheer volume. Pop music has always been played loud, but albums used to be mastered to retain as much of the dynamic range as possible. Dynamic range means that the quiet parts are quiet, which makes the chorus even more powerful when the guitars kick in and blow the roof off the place.

Now songs are blisteringly loud from start to finish. At first, it's exciting, which is exactly what the music executives want. But after listening to a couple of songs in a row at this hyperinflated volume, listeners begin to suffer from ear fatigue. It's not that their ears physically hurt, it's that they get tired of the flatness of the music. They get tired of trying to listen for sonic details, the clear sounds of different instruments, the warm subtleties of the human voice that just aren't there anymore.

Audio enthusiasts have long complained about the damage being inflicted on music and listeners by the loudness war. Even widely respected artists are falling prey to the pressure to make their tracks as loud as the latest My Chemical Romance song. Led Zeppelin's remastered collection, "Mothership"  -- mastered by Jimmy Page himself -- was criticized by some listeners as being simply too loud [source: Levine]. Even folk stalwart Paul Simon has received cranky comments about his 2006 album "Surprise" [source: Anderson].

The chief complaint, therefore, with remastered CDs is that instead of reaching back and restoring music to its highest possible quality, music producers are just selling louder, flatter versions of the same old songs.

For even more information about audio editing and the music business, follow the links on the next page.


Lots More Information - Remaster CDs/DVDs


Related HowStuffWorks Articles

More Great Links

  • "The Death of High Fidelity." Levine, Robert. Rolling Stone. Dec. 27, 2007. (
  • "The Elements of Home Studio Audio Mastering."Tweakheadz Lab. (
  • "Glossary: Compressor" Sweetwater. (
  • "Glossary: Mastering" Sweetwater. (
  • "How CDs are remastering the art of noise." Anderson, Tim. The Guardian. January 18, 2007. (
  • "How Criterion Hones its Restoration Magic for HD." Frucci, Adam. Gizmodo. September 25, 2008. (
  • "What is Mastering?" DRT Mastering. (
  • "What's the Difference? CD 'Mastering' vs. 'Remastering.'" Guttenberg, Steve. CNET February 12, 2008. (