Digital Music Players Change CD Mastering

The iPod is changing the way musicians and engineers create music CDs.

With digital music players and music-download stores, the playlist is replacing the album as the primary collection of music. Music fans are buying more singles, or individual songs, and fewer albums, and then are putting the songs together in completely unique sequences. The shuffle or random play feature of CD changers, iTunes, and the iPod, which select the next song at random from a large set of songs or even an entire music collection, creates the ultimate in unique song sequencing, in which you may never hear a song in the same context twice.

In the old days, albums were put together with the idea that music fans would listen to the entire album. The sequence of tracks was of utmost importance, and engineers pored over every transition from one song to the next, even deciding exactly how many milliseconds of silence between two tracks would create the best musical effect.

But the gaps between tracks are lost in shuffle mode. And how can engineers optimize the transitions between songs when no one knows in advance what playlists the songs might appear in, or even how many seconds of crossfade a listener might use for transitions between tracks?

The new realities of music playback have changed the way engineers approach CD mastering. It’s not about the gaps between tracks anymore. Most mastering engineers have stopped using gaps between CD tracks (some purists, it must be said, had objected to them all along, even back in the LP era) and are incorporating any needed silence between songs into the tracks themselves. It used to be that in a well-engineered CD track, the song would start within one eighth of a second of the beginning of the track. Now some tracks start with a second or two of silence to ensure that the initial downbeat of the song doesn’t get lost in whatever song came before.

Gaps between CD tracks are still used in special situations. You might find a gap of several seconds between the studio tracks on a CD and the live bonus tracks that follow, for example.

Engineers are also paying less attention to the volume levels of consecutive songs and the overall level of an album. It is just as important now for the volume of a song to be correct when it pops up in a playlist with songs from 10 or 100 other albums. And so, engineers are mastering album tracks now knowing that each track will be used as a single. There is more risk in trying to maximize the volume of an album. The songs could sound bad taken out of context. Songs that sound bad are the first to get deleted, so engineers need to master songs to fit in, not to stick out.

In other words, album mastering has all but turned into single mastering. This simplifies the process of mastering a CD. Master each song correctly, then make a playlist of them, and if the playlist sounds good, you can burn the CD.

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