Ripping

Ripping is transferring the content of a CD to a hard disk.

Ripping is a bit different form making a copy
The content is not only read but also transformed at the same time to an audio file format a PC can understand.

Bit perfect

The true audiophile worries: ‘is the rip bit perfect?’

Audio CD

By design a bit perfect copy is not guaranteed.
This is inherent to the CD audio standard (Redbook).

At design time, they decided to maximize capacity at the expense of bit perfect reading.
An audio CD uses all 2352 bytes per block for sound samples.
A CD-ROM (bit perfect reading guaranteed) only 2048 bytes. The remainder is used for error correction code.
A 15% reduction in capacity compared with the audio CD.

 

It is true that audio CDs use all 2352 bytes per block for sound samples, while CD-ROMs use only 2048 bytes per block, with most of the rest going to ECC (Error Correcting Code) data. The error correction that keeps your CDs sounding the way they're supposed to, even when scratched or dirty, is applied at a lower level. So while there isn't as much protection on an audio CD as there is on a CD-ROM, there's still enough to provide perfect or near-perfect sound quality under adverse conditions.

 

All of the data written to a CD uses CIRC (Cross-Interleaved Reed-Solomon Code) encoding. Every CD has two layers of error correction, called C1 and C2. C1 corrects bit errors at the lowest level, C2 applies to bytes in a frame (24 bytes per frame, 98 frames per sector). In addition, the data is interleaved and spread over a large arc. (This is why you should always clean CDs from the center out, not in a circular motion. A circular scratch causes multiple errors within a frame, while a radial scratch distributes the errors across multiple frames.)

 

If there are too many errors, the CD player will interpolate samples to get a reasonable value. This way you don't get nasty clicks and pops in your music, even if the CD is dirty and the errors are uncorrectable. Interpolating adjacent data bytes on a CD-ROM wouldn't work very well, so the data is returned without the interpolation. The second level of ECC and EDC (Error Detection Codes) works to make sure your CD-ROM stays readable with even more errors.

It should be noted that not all CD players are created equal. There are different strategies for decoding CIRC, some better than others.

 

Andy McFadden

The lowest level is "EFM" or eight-to-fourteen modulation". It takes each byte, and turns it into 14 bits in a fashion wherein it is possible to both correct many misreads as well as tell when a misread is uncorrectable.

Then there is an interleaving, to allow for scratches, holes, pits, etc in the CD data layer.

After that a reed-solomon code is used to error correct and error check again.

After that, if the RSC can't get it right, the player either interpolates (for a block or two) or mutes.

On most CDs there is almost nothing getting past the reed-solomon code. Usually in fact nothing at all

 

Source: http://www.hydrogenaudio.org/

 

The amount of reading errors is related to the quality of the CD, noticeable the amount of scratches.
Some think you need a special high quality CD-reader to avoid reading errors as much as possible.
Plextor is often mentioned but they stopped producing their own optical drives years ago.

 

The funny thing is, that the low cost CD723 player is able to read any CD or CD-R that is not severely scratched without any interpolation or hold. You can even put it upside down, there will be zero interpolation /hold.

Uncorrected samples could only be generated by dropping the player (5cm) or by extremely scratched CDs.

 

Source: http://www.jitter.de

Ripping a CD is different from playing a CD.
When playing, the correct speed is important as the output of the CD transport goes straight to the DAC. Ripping has nothing to do with real time, some rippers use this to read a damaged  part up to 80 times to establish the most likely value.  


The AccurateRip database tells you if your rip is accurate or not.
It can be used the other way around too, how many rips are accurate given a certain brand/model.

Obvious they do differ: CD/DVD Drive Accuracy List 2016

Sample rate and bit depth

By design a audio CD contains PCM audio with 16-bit words and a 44.1 kHz sample rate.
If not it doesn’t comply with the CD audio standards (Redbook) and won’t play.


Sometimes people ask if it does make sense to rip to 24 bits and/or a higher sample rate.

You can rip (or convert) to 24 bits.
This will simply add 8 zero bits to each sample. They don't contain any musical information.


As the sample rate is 44.1, the highest frequency on a CD is 44.1/2=22 kHz (in practice slightly less). This is inherent to the Shannon/Nyquist sampling theorem.
Ripping to a higher sample rate won’t add audio > 22 kHz because it is simply not on the CD.

 

Sometimes CDs upsampled to a higher rate (or upsampled on the fly) do sound different.
This is because some DACs do change their sonic signature when feed with higher bitrates.
Some calls this different sound an improvement, others a design flaw…

Ripping software

One of the many comparison between various rips has been made by Kent Poon.
Comparing rips made on PC and MAC using iTunes, Wavelab and EAC didn't show any difference.

 

Soundcheck compared different ripping programs and optical drives.

Under certain conditions the tested drives and tools deliver 100% identical results. From that perspective there shouldn't be any difference on SQ.
If you'd don't use Accurate Rip drive-offsets, every rip will be different on every drive. And that might be an issue.

When it comes to the extraction tools. They pretty much all deliver exactly the
same data - if the setup is correct.

soundcheck's - audio@vise

 

If you want to be nuke proof, there are two powerful rippers Exact Audio Copy (EAC for short) and dBpoweramp. Both employ all the tricks to get a bit perfect copy.
Both can be combined with AccurateRip to verify the results.

See the software section for more details.

 

...all CD Ripping programs, all brands of DVD and CD drive will rip bit perfect (drive offset accounted for, BTW the offset is not audible past the first micro-seconds of a track) on the majority (over 95%) of undamaged discs. The differences in CD ripping software: ability to detect errors, potentially correct errors (by re-reading) and eventually report errors if they cannot be corrected.

Spoon (developer dBpoweramp)

Ripping errors

Redbook audio is 2 channel of 16 bits with a frequency of 44100 Hz.
2 x 16 x 44100= 1411200 bits/sec
A 5 minute track contains 423,360,000 bits.
An hour 5,080,320,000 bits.

Makes you wonder how it is possible to read an entire CD bit perfect.

 

Suppose you go for the best: dBpoweramp.
Now you are confronted with ripping errors.
Do they matter?

 

Usually if there are problems with a CD it's only in one track. dBpoweramp will also report how many problem frames are involved (75 frames per second). Often there is just one frame that's bad. If you go and listen to the track then there is a 50-50 chance you won't hear anything wrong. If you own a CD and it rips with errors and you want to listen to it, then just do so. You may be pleasantly surprised that the error are inaudible.

If you get errors on more than a small fraction of your disks and the disks have no obvious problems then it is likely that your drive isn't working so well. The best thing to do then is to try reading the problem disk on a different drive, e.g. on a different computer.

I haven't seen a pattern on whether EAC or dBpoweramp does better on the marginal disks. I have seen a pattern when using different drives.

Tony Lauck

File format

Today a 1 Tb HD sells at € 100,-
You can store approximately 1600 CD’s on it if you choose a uncompressed lossless format like WAV. A format like FLAC does lossless compression up to 50-60%.

As storage is cheap today, I recommend ripping to a lossless format.

More about audio file formats.

Storage

Ripping your CDs or vinyl to your hard disk requires some space

A storage calculator can be found here

References
  1. My results for secure ripping - Old Listener
  2. CD ripping - Kent Poon
  3. CD/DVD Drive Accuracy List 2012 - Illustrate
  4. CD-Recordable FAQ - Andy McFadden
  5. CD/DVD Drive Accuracy List 2016 - dBpoweramp