Audio Basis - educational articles
Read answers to frequently asked questions on topic "How to convert 1-bit ISO (a.k.a. SACD ISO) to DSF".
In general, the best CD ripper should provide minimal number of ripping errors comparing other ones.
Unfortunately, there are not research results, that known to the author.
Read details here >
Also important CD ripper ability is automatic obtaining metadata from Internet.
CD ripper should provide minimal number of reading errors. After reading CD the audio stuff should be stored to sound file without losses. Audio file formats WAV, FLAC, AIFF, ALAC allow to store audio data binary identical to the reading content.
More recommendations read here >
Most important ripper ability is minimization of reading error number. As rule, for users, sureness in error detection is very important.
Compact disk standard provides for error detection and recovering. But without 100% guarantee of error detection.
CD ripping errors may have several levels of detecting and elimination:
CD ripper also don't provide 100% error detection.
Read more about safe CD ripping here here >
Many CD rippers can access to online databases to obtain track name, album, performer, etc. As rule, CD riper generate unique ID of CD, based on CD data (it is not a standard ID). This ID may be different for different database.
Information is queried from the database by this ID. Sometimes several metadata options may be stored in the database for single CD.
There are databases with album artworks.
Databases with CD metadata: freedb.org Discogs Gracenote
Mac OSX allow to copy CD audio tracks from CD to hard disk as usual .aiff files. Author suppose, that there is used same way as ripping in iTunes.
If you use other CD ripping software, there may be used other error detection way. Probably (no guarantee) it allow to detect errors, that are not detected during copying .aiff.
Read more how ripper software may copy CD here >
Under Windows at CD audio disk we can see .cda files. But these files have too small size for music. Also copying these files don't allow copy music.
.cda files are not musical files. It is index files only, that points to track.
CD have table of content (TOC), that contains positions of the tracks into solid raw audio stream. These positions contains into .cda files.
To copy audio data, CD rippers read the table of content (as rule, directly - without .cda files) and read tracks from CD's raw audio stream according track positions.
Yes. You can use CD rippers, that support FLAC format.
Yes. You can use CD rippers, that support AIFF and ALAC formats.
If lossless formats (WAV, FLAC, AIFF, ALAC, other) is used to rip CD into audio files, format is not matter.
When you use lossy file formats (mp3, aac, other) sound quality depend on format and its codec settings.
Read more about ripping formats here >
Audio files mp3, wav, aiff, dsf uses ID3 metadata standard.
FLAC use VORBIS standard.
Also WAV can use LIST chunk (data block) with metadata information.
These formats are compatible in general. But some format converting matters may be applied different ways. It can cause compatibility issues. Also not all metadata information by music provider may be described into metadata standards. Though latest standard versions have wide range of formalized information kinds.
Many software may read these formats. But there are may be reading and displaying issues.
In the table difference between CD ripper computer software and CD player (musical device) is shown.
| CD ripper (computer software) | CD player (musical device) | |
|---|---|---|
| Reading raw digital stream | Yes | Yes |
| Smart interpolation of damaged raw data fragment | Author don't know such implementations | Yes |
| Low level error detection and correction into optical device | Yes | Yes |
| Higher level error detection and correction (statistical processing) | Depend on implementation | Author don't know such implementations |
| Pre-emphasis correction | Depend on implementation | Yes |
| Reading CD-text | Depend on implementation | Depend on implementation |
| Reading track metadata (track name, album, performer, artwork, etc.) from internet database | Depend on implementation | Author don't know such implementations |
| Decoding HDCD | Depend on implementation | Depend on implementation |
There are may be issues:
Modern CD rippers have access to digital audio stream from CD directly.
Author suppose, that pre-emphasis is not used at modern CDs.
Also sound quality depend on error correction ability of CD-drive and ripping software.
Sound quality for CD ripping is CD-reading error number.
Theoretically, it is possibly, if it is many insignificant errors in lowest bits of 16-bit sample. But this case have very low probability in the real life.
As rule, incorrect CD reading cause coarse sound distortions:
CD player (musical device) may try fix some these issues via interpolation.
If CD's raw data stream is read under Mac OSX and Windows same way, there is no difference.
But different ripping software may have different algorithms of CD reading. So we can get different result (error number) for different software independently on operation system.
If CD is read stable (without errors), there is no dependence on operation system or CD ripper software or optical disk.
Different optical CD-drives can cause different reading-error number. But it is coarse errors (silence, clicks, etc.) rather.
Pre-emphasis is noise reduction method. It implemented via high frequency boosting in the audio stuff recorded on CD.
During playback applied inverse boosting (filtering, de-emphasis) of high frequencies.
If pre-emphasis correction is not compensated, degrading sound quality may be caused.
If pre-emphasis is applied on CD, it is written as special flag on the CD.
As author know, pre-emphasis was used at some old CDs.
Safe CD ripping use multiple re-readings of the same fragments of the compact disk's audio stream. Each re-reading consume additional time.
CD reading speed depend on error number or reading issues, that have this CD. As example, places with detected errors may be re-readed additionally by CD-drive and ripper software.
CD rippers may use different methods of CD reading or different parameters of the same method.
When you rip CD to mp3, you can't restore original content of CD.
C2 if flag, that display CD ripping error, generated by optical CD-drive.
One C2 flag show reading state of one byte of raw audio data from CD.
Implementation of C2 may be different.
C2 flag don't obligatorily mean, that raw data at optical drive output is damaged.
CD ripping online database (checksum database) collect checksums of ripped CD's. New ripped CD may be compared with checksums of same CD's.
If there is difference in just ripped and collected checksums, probably there is ripping error. Read more below.
The database contains big number of CDs. However, no warranty, that rare CD will contains in the database.
CD-drive and ripper as system can detect CD-ripping errors. Different systems have different error detection probabiity.
Checksum database is filled from uncertified sources. Checksum calculated by ripped stuff instead files that was used to producing of the CD.
In general, there is no way of correct error detection with 100% probability. Correct error detection probability of the database is unknown.
So we don't know exactly, that correct error detection is better (that correct error detection probability is higher): CD-ripper+drive system's or checksum database's.
Read details here >
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