Audio Basis - educational articles
CD ripper software intended for copying CD audio content to music files at hard disc of a computer. Sound quality issues, different ripping ways (including safe/secure and unsecure), ripping formats and settings, metadata management are revieved.
Read in this article how to choose the best CD ripping software for audiophile.
You can meet topic of the article too often at the forums and articles, like: "the best cd ripping software 2017", "the best cd ripper 2017", "the best cd ripper for mac", "the best cd ripper for windows", etc. The rippers are compared by perceived sound quality, functionality, metadata (song information: track name, album, performer, etc.) abilities, ripping speed and other.
However, in my opinion, main feature of the best cd ripping software for audiophiles is exactness of copying CD's binary audio information to music files.
This feature is measurable. But it is not available at public access.
Safe CD ripper or secure CD ripper is the ripper software that have the binary-content-copying exactness as aim.
Read below:
Read below review of audio data integrity control (quality issues), ripping speed and audio-information restoration.
Quality of CD ripping is number of broken bytes in the ripped files.
CD ripping error is digital audio data difference between original record and ripped file.
Original record is audio file that used to produce compact disc.
Correct error detection is correct detection of real broken byte.
False error detection is fault on correct music information.
Abbreviations
Maximal CD ripping quality is ripping without errors. I.e. binary music content of ripped file is fully identical to original record.
Aim of safe CD ripping software
In the first approach, CD ripping software can't improve sound of CD.
The best thing that can to do the software is binary exact copy of music information from optical disc to sound file only.
However, there are some details. If computer optical drive provide lesser reading error number, than audio optical disc player, ripped sound files can be closer to original master record than digital music stream, that read on the CD-player. It was important to remember, that hardware players have own ways of probable broken music restoration.
The word "probably" is used too often in the article, because error rising, correct or false error detection, error fixing are not events with 100% probability.
Digital music stream faults can cause either clicks or pauses or interruptions or other audible distortions.
There are different ways of the ripping error detection:
CD ripping ways (secure / non-secure)
In this case CD audio stream is read:
- without error flags,
- without re-readings,
- with buffering of read information.
Audio information is corrected by optical drive anyway.
But there are some ways of additional ED are missed (read details "Low level CD-fault detection" part).
Sometimes optical device driver of operation system is able to report about fault, sometimes - not (depend on implementation driver and operation system). CD ripper don't obtain to error flags, generated by compact disc drive, and store music information as is into files.
This secure way calculate ripped CD's checksum. These checksums are collected into internet database. When you rip CD at the database compatible ripping software, your rip checksum is calculated and compared with checksums into the database.
Checksum comparison via CD-ripping checksum database
But the database don't contains original record checksum. So ripped checksum compared with array of uncertified checksums. We can hope (without 100% warranty), that the majority of similar checksums for some CD into the database is the same checksum of the CD's original record.
Also there may rare record or different optical disc version (pressing) issues.
This secure/safe way based on:
CD-drive is able to correct faults and restore (with some probability) valid audio information (Reed–Solomon coding) [1][2].
So compact disc drive try detect fault inside. If it is detected, the drive try to restore music information. In case of unsuccessful fault elimination, error flag (C2) mark broken byte.
The safe/secure compact disc ripper software may to apply additional fault detection and correction algorithm under data, that was before checked and corrected into CD drive.
Low level CD-ripping fault detection
Raw audio stream from CD-drive is read with C2 flags, re-readings and with buffering elimination of read data.
Several re-readings of CD-drive's music data, can cause different binary content for re-readings.
This difference combined with С2 flags can give new information about faults, that was probable missed into CD-drive.
One error flag control audio data integrity of 1 byte of the raw audio information. The flag calculated by CD drive. Probably, some drives can't calculate it. But, I suppose, it is matter of older drives.
Re-reading is repeated reading of CD track's fragment. Re-reading performed several times.
Buffering elimination is attempt of forced cleaning of CD data buffer for each re-reading. Re-reading from music data buffer have no sense, because there are same information for each re-reading. But repeatable audio data reading from CD can cause different content in problematical places.
Further the obtained data array is analized to additional ED.
This method also don't guarantee 100% probability of audio stream integrity.
However, there is no additional element of uncertainty like a database without original record checksum.
CD extractor can begin to read information from maximal speed to save time. When compact disc ripper read music information and get fault (as from optical disc drive, as by the data analysis), it can reduce reading speed to safer extracting. Of course, it consume more time.
CD rip speed vs. quality
Ripping speed depend on own CD drive's correct reading ability.
CD reading speed should provide maximal available safety of extracted music information.
If CD ripper use re-readings, it decrease total ripping speed anyway, even for constant rotary speed.
Because in safe/secure mode compact disc is read several times, instead one time in unsafe mode.
Correct error-detection is event when both sources (safe CD ripper and checksum database) detected "ripped information is valid".
Total correct error-detection probability (CEDP) of the safe ripper:
CEDPcd is [CD drive + CD ripper] system's correct ED probability (CEDPcd <= 1.0)
CEDPdb is the dababase's correct ED probability (CEDPdb <= 1.0)
Ideal theoretical value of CEDPcd and CEDPdb is 1.0. But real values are lesser 1.0 always.
CD rip fault detection probability with checksum database and without
Result of multiplication CEDPcd to value, that lesser 1, is lesser than CEDPcd.
Thus, CEDPwd < CEDPwod ("with database" lesser than "without").
There is no known information, what is higher: correct ED probability of [CD drive+ripper software] system or database.
Simultaneous using of both methods reduce total correct error-detection probability of CD ripping.
Generally, separate using only one of these two methods is recommended to decrease result uncertainty.
You can choose method, that is more suitable for you by other functionality (data restoration, as example, or other).
Though mistake in method choice can cause lesser total correct error detection probability.
The ripper software read data array (raw audio data and error flags after several re-readings) and use it to create probable correct content at damaged places (without 100% guarantee, of course).
Some data can't be restored (fatal faults).
If your aim is binary audio data capturing as is, use any lossless PCM format (WAV, FLAC, AIFF, ALAC, APE, etc.).
If your aim is lossless file size reducing, use FLAC.
If your aim is maximal file size reducing - use mp3 or AAC format.
However, for optical discs, ripping to backups in lossless file formats (WAV, FLAC, AIFF) is recommended.
After it you can convert these lossless backups to mp3, DSF or other format.
It allow to save time of slow audiophile ripping procedure.
Most complex ripping part is safe reading from optical disc. For some discs it may be unstable.
Generally ripping into 16 bit / 44.1 kHz PCM backup (WAV, FLAC, AIFF, etc.) without any processing is recommended.
Check your CD ripper settings to turn off any processings (resampling, dithering, gain, etc.).
These ripped backups you can use for further conversions to target musical devices (portable audio player, mobile phone, car audio, music server, etc.).
Fortunately we can objectively compare CD rippers by ripping quality.
This comparison can't cover all cases. Because test result can depend on damaging kind of test CD.
1. Tools
1.1. CD rippers
1.2. CD-drive(s)
1.3. Test CDs with binary identical WAV files per track.
The test CDs should have different
1.4. Tool for binary comparison of WAV files.
2. Testing rippers
2.1. Rip the test CDs to WAV files for different combinations:
a) CD ripper software
b) Compact disc drive
c) CD ripping mode (speed, overlapping, re-reading number, recovering, etc.) if available.
2.2. Compare ripped WAV files with original files (sources of tracks of the test CDs) via binary comparison tool (goal 1.4):
a) Length in bytes from begin of the track to first detected (via binary comparison) fault byte.
Register it in results as mark of steadiness CD extractor to fault appearing.
b) Percent of detected (via binary comparison) wrong bytes to total number of bytes in track.
Register it in results asmark of ability CD extractor to fault avoiding.
During WAV file binary comparison need consider audio data only (pass by WAV’s header and non-audio chunks).
Recommended provide several times (10 and more) rippings in combination
{[test CD]+[CD ripper]+[CD ripping mode]+[CD drive]}
It is need to be addressed possible byte offset between original WAVs and ripped ones.
If the offset is present, superpose original and ripped WAV files.
To superpose refer to identical binary sequences of audio data. Found identical binary sequences in original and ripped WAV files and shift compared binary content to match the sequences.
As begin of track considered begin of original WAV's audio data.
3. Comparing results of the tests
Integral mark of the tested system [ripper + ripping mode + CD drive] is averaged by different test CDs.
Resume of test are made by comparison of the integral marks of the systems.
Some CD rippers are able automatically request track's metadata (metatags): song and album name, year, performer for internet database.
Some databases contains album artworks.
When ripping is started, the ripper form unique ID of compact disc by its track start addresses, as example.
Sometimes database contains several entries for single disc. As example, at different languages.
Some rippers enable to assign metadata and/or album artwork file manyally before or after ripping.
There are databases:
Free:
Commercial (with some non-commercial options):
Main useful audio ripper feature is copying exactness of audio data from compact disc to file. In the ideal case the data should be extracted without changes.
For valid CDs it is not matter. In the first approach, all CD rippers will work identically there. Except false error detection case.
But some CDs, especially damaged, may contains errors. And CD extractor should found the faults. It's desirable, the ripping software attempt to restore damaged data that was found.
I.e. we can choose (as the best) the ripper that makes minimal fault number in ripped data.
In the article comparison method of audio rippers is suggested.
Unfortunately, I don't met results of independent ripper quality researches in the open sources.
Using checksum database allow to compare own ripping results with other ones, but original record checksum is unknown.
I'd recommend to choose one of CD rippers (free or paid), that have low level error detection with CD drive, providing C2 error flags. It enables the direct control over ripping errors without referring to uncertified third party sources.
Simultaneous both method using is not recommended, because probable case that both methods show different results.
The simultaneous using can reduce probability of correct error detection.
Yuri Korzunov,
Audiophile Inventory's developer
21 May 2016 / updated 15 July 2017
Video: How to polish optical discs scratches
References
Copyright © Yuri Korzunov
["Audiophile Inventory" (since 2011), "AudiVentory", "Audiophile Inventory by AudiVentory.com".
Также "Audiophile Inventory by AudiVentory.com" (прежде "Audiophile Inventory") охраняемое коммерческое обозначение],
2010-2018. All Rights Reserved.
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