Ripping CDs: how to make a bit-perfect copy

Why ripping is harder than it looks

The audio CD dates from 1980, defined in the so-called Red Book by Philips and Sony. It was built for CD players, not computers. Music sits on it as one long data stream without a file system, with error correction that compensates for scratches and dust up to a point.

When that correction isn't enough, a CD player simply calculates the missing bits from neighbouring values. You almost never notice while listening. Many computer drives do the same when reading, without reporting it. A simple program such as the Music app then receives data that looks plausible but isn't what's on the disc. The result usually sounds fine but is no longer an exact copy. With badly damaged discs you hear clicks, dropouts or short repeats.

Two technical quirks add to this:

• Drive cache: many drives buffer data they've read. When a program reads a spot a second time to check it, it may only get the cached copy rather than a fresh read.
• Read offset: almost every drive starts reading a few samples too early or too late. It makes no audible difference, but it matters for an exact comparison with other rips.

Good ripping programs therefore work differently: they read each spot several times, get around the cache, compare the results and finally check the finished copy against a database.

What you need

A drive

Most current computers no longer have an optical drive. Apple dropped its external USB SuperDrive in 2024 after 16 years. External USB DVD burners from many brands cost $25 to $40 and work on Mac and PC without drivers. On a USB-C Mac a simple adapter does the job. The only thing that matters is enough power: if the drive doesn't spin up properly on a hub, plug it in directly.

A particularly expensive drive brings little. Because the program verifies the result, you'll know immediately if a drive struggles. At most, a second drive from a different maker helps with difficult discs.

A program

The Music app can import CDs as Apple Lossless and has an error correction option for reading. It doesn't check the result against a database, though, so you don't know whether the copy is exact. For an archive meant to last decades, XLD or EAC is worth it.

Space

A CD takes around 250 to 350 MB as FLAC on average, depending on length and music, so 500 CDs fit in about 150 GB. How to combine that with a smaller copy for your phone is covered in organising a music library.

Set it up properly, once

Labels differ between programs and versions, but the settings behind them are the same everywhere. You do this once; afterwards you just insert CDs.

Read offset

The offset is given in samples. At CD quality one sample is 1/44,100 of a second, so an offset of +667 is about 15 milliseconds. The AccurateRip database keeps a list of offsets for thousands of drive models. EAC and XLD can determine the value automatically: insert a well-known CD, the program compares it with the database and fills in the right value. Without the correct offset the rip sounds the same but can't be compared with other rips.

Secure read mode

Every good program has a mode that reads carefully rather than fast. In XLD it's called "XLD Secure Ripper", in EAC "Secure Mode". Important companion settings:

• Defeat the cache: EAC can detect whether the drive caches audio data and compensate for it. XLD's Secure Ripper has its own mechanisms for this.
• Test and copy: in EAC, "Test & Copy" reads every track twice and compares the checksums. It takes twice as long but gives good evidence even for discs no database knows.
• C2 error pointers: some drives report uncertain spots themselves. That can speed things up but isn't reliable on every drive. When in doubt leave it off; the database check is the safer proof.

Verification databases

Turn on both where you can:

• AccurateRip has collected checksums of rips from around the world for many years. If your checksum for a track matches others, the track is error-free. The "confidence" tells you how many other rips agree with yours.
• The CUETools database (CTDB) goes a step further: for each disc it also stores small repair records. They allow smaller read errors to be corrected afterwards; according to the project, at best one continuous damaged area of 30 to 40 sectors, about half a second.

Output: format, names, tags

• Format: FLAC, compression level 5 to 8. The level only changes size and time, never quality. If you stay entirely within Apple's world, ALAC works too. Why these two are the right choice is in music file formats explained.
• File names: for example Album Artist/Album (Year)/01 Title.flac, with the disc number in front for multi-disc sets.
• Tags: the programs identify the CD by its table of contents and fetch titles, artists and year from online databases such as MusicBrainz. Check the data before you start. Album artist and spellings deserve a look in particular, because they decide later whether your player sees the album as one.
• Artwork: embedded, 1,000 to 1,500 pixels is plenty. Larger images cost space in every track.

Gaps between tracks

A CD can have gaps between tracks that belong to the previous or next track. For separate files, programs append these gaps to the end of the previous track by default. If your player plays gaplessly, you get the same flow as on the CD, live albums and continuous concept albums included. If you want to burn the CD again exactly later, also write a CUE sheet that describes every gap and index mark.

A special case is a hidden track before the first track, known as Hidden Track One Audio. It sits in the gap before track 1, and a normal player only finds it if you rewind from the start of the first track. EAC and XLD can detect such areas and save them as a separate file, though not every drive can read them.

A rip, step by step

• Check and clean the disc. Wipe off fingerprints and dust with a soft, lint-free cloth, straight from the centre outwards, not in circles. Circular scratches follow the data track and are harder to correct.
• Insert and check the metadata. The program shows the recognised tracks. Fix album artist, album title and year before you start.
• Start ripping. In secure mode a well-kept CD usually takes a few minutes up to about a quarter of an hour. Damaged discs can take much longer, because the program rereads problem spots again and again.
• Check the log. Every track should be confirmed as error-free. How to read the messages is in the next section.
• Keep the log. Save the log file in the album folder. It's your proof that the copy was verified.

Reading the log

At the end every good program writes a log. The wording varies, the meaning is the same:

A common reason for "not in the database": the same CD exists in several pressings, from different countries or years, which are mastered or offset slightly differently. Yours may simply not be recorded yet. In that case good programs sometimes report that the rip matches another pressing with an offset. That also counts as confirmed.

Scratches, special cases, copy protection

Scratched discs

The order that works: clean, rip in secure mode, repair errors with the CUETools database, and if that's not enough, try another drive. Drives from different makers often read difficult spots differently well. Resurfacing with special machines sometimes helps but can also do damage. It's only worth it when everything else fails and the disc can't be replaced anyway; a second-hand copy often costs less time.

Burned CD-Rs

Home-burned discs age much faster than pressed ones. If you have old CD-Rs, such as concert recordings or demos, rip them soon. They're in no database, so secure mode and double reads are what count.

Pre-emphasis

Some early CDs from the 1980s were recorded with a treble boost that the CD player reverses on playback. A flag on the disc tells the player to do so. Many ripping programs copy the data correctly but ignore the flag, and the result sounds too bright and harsh. EAC and dBpoweramp display the flag. Affected rips can be corrected afterwards with a de-emphasis filter, for example with the free command-line program SoX and its deemph effect. Ideally keep both the untouched rip and the corrected version.

Copy-protected CDs

Roughly between 2001 and 2006, labels released CDs with copy protection, often with logos like "Copy Control". Technically many of them violated the CD standard and wouldn't play in some players at all. A notorious case was Sony BMG's copy protection software in 2005, which quietly installed itself deep inside Windows and was recalled after public criticism. Circumventing such protection is prohibited in many countries even for private copies; for these discs a regular download is often the simpler route.

Is it allowed?

That depends on where you live. Germany permits individual private copies of CDs you own as long as no effective copy protection is circumvented. In the UK, a private copying exception was quashed by the High Court in 2015. In the US there's no explicit statute; personal format-shifting is widely regarded as fair use but hasn't been settled by a court. Everywhere, copies must not be sold or shared. More on this and on alternatives such as DRM-free downloads is in the article on building a digital music archive of your own.

After the rip

• Check tags and artwork, ideally once per album in your player. Duplicate album tiles are almost always a sign of inconsistent album artists.
• Back up. A rip that lives on one drive is gone when that drive fails. The 3-2-1 rule and how to verify files with the FLAC checksum are covered in the archive article.
• Listen. In Luma for Mac you simply add the folder with your rips, nothing gets copied. Luma Transfer sends the albums to your iPhone over Wi-Fi or cable, tags and embedded artwork included.

Frequently asked questions

Sources

• AccurateRip, database of CD rip checksums and drive offsets. accuraterip.com
• CUETools Wiki: CUETools Database (CTDB), verification and repair of rips. cue.tools/wiki/CTDB
• XLD (X Lossless Decoder), official project page. tmkk.undo.jp/xld/index_e.html
• Exact Audio Copy, official project page. exactaudiocopy.de
• Apple discontinues the USB SuperDrive (9to5Mac, August 2024). 9to5mac.com/2024/08/05/apple-superdrive-discontinued
• Archimago: CD pre-emphasis and dealing with it (2020). archimago.blogspot.com
• High Court quashes the UK private copying exception, July 2015 (IPcopy). ipcopy.blog/2015/07/21/high-court-quashes-private-copying-exception

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