The “Redbook” CD specifications state that CDs contain a maximum of 74 or 80 minutes of music. But over the years, record producers have tried to push that limit. There have been some CDs released that approach the 90-minute mark, but I suspect that these are CD-Rs – individual burned CDs – because this is possible using “overburning.”
But I’ve been seeing a lot of CDs recently that are longer than 80 minutes. In the Mozart 225 box set, many of the CDs exceed this duration, and some are even longer than 85 minutes. The longest CD in this set clocks in at 86:30.
This isn’t a problem if you’re playing back the CDs on recent devices, or trying to rip them to a computer, but older CD players may not support these discs because the track that spirals around the disc are too close together for older players to read.
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Many fans of older music probably have a lot of CDs in mono. Early classical recordings, old blues discs, and jazz up until the 1950s was all recorded in mono. Even later music is available in mono mixes, notably many of The Beatles’ recordings and early discs by Bob Dylan. If you rip these discs in iTunes, they are generally ripped in stereo. iTunes’ settings suggest that you can choose to rip with channels determined “automatically,” but this never results in mono files when I rip mono CDs; I always get stereo. (I don’t mean that the music is in stereo, rather that iTunes creates stereo files where the two channels are exactly the same.)
You may want to rip in mono to save space. There’s no reason to rip a mono CD in stereo; the resulting files contain exactly the same data on two channels rather than one, and take up twice as much space.
To rip in mono, you need to choose Mono from the Channels menu in the Import Settings > Custom window. And you need to remember to make this change both before and after ripping any mono CDs you have. Note that to choose a bit rate for mono rips, you need to choose the double of that bit rate. In other words, if you choose 256 kbps, the mono files will be 128 kbps; the bit rate you choose is the stereo bit rate.
One thing to keep in mind is that if you use iTunes Match, make sure you don’t choose a bit rate below 192 kbps (which will result in 96 kbps mono files). ITunes Match won’t accept files that are less than 96 kbps, so you won’t be able to match those files.