Ripping off recordings DIGITAL AUDIO EXTRACTION DO'S, DON'TS AND DO'ERS - Statistical Data Included

Emedia Professional, July, 1999 by Robert A. Starrett

We all know that the Red Book--the original CD standard--defines CD-Audio, and that the compact disc for one purpose: to store and play music in digital format. Designed initially to be nothing more or less than a universal delivery medium for music digitized at 44,100 samples per second (44.1KHz) and in a range of 65,536 possible values (16 bits), Red Book, or Compact Disc-Digital Audio (CD-DA), was defined by Philips N.V. and Sony Corporation in 1980. It was an overwhelming--if not quite instant--success, and today, with inexpensive tools and recorders, the average consumer can do much more with audio CDs than play them back on their stereo systems. Technology available today--though internally complex--renders quite simple, accessible, and relatively inexpensive the enticing prospect of extracting and re-recording the original Red Book data to make custom compilation CDs of any music enthusiast's favorite tunes.

The downside of it all is that the careless, the pirate, and the criminal take great advantage of these inexpensive tools and recorders for the illegal distribution of compilations of copyrighted songs or complete album copies. This musical contraband can be stored and distributed on CD-R, by pressed disc, or in MP3 format, and sold at discounts, leaving the artist, the recording company, and the songwriter without royalties--in essence, without payment for their work. But audio extraction also supports not-for-profit private pleasures, of course, and plays a key role in the back-end infrastructure of today's increasingly popular Web-driven custom audio CD services. While using the same enabling technology as the pirates and bootleggers, such Web-based businesses as customdisc.com and supersonicboom.com are upstanding, royalty-paying enterprises who offer alternate music distribution (and technology) models fully approved and accredited by the music industry, powers-that-be.

Whatever your purpose, accurately extracting a Red Book track from a CD has always been more challenging than copying a file from a CD-ROM to a hard drive. Red Book tracks are not files, per se. They are made up of a bunch of data that is meant to stream, and within the stream there is more than music. The stream itself is not a straight stream, it is interleaved; that is, portions that naturally follow each other in a song do not follow each other on the disc itself. You can easily record an analog version of a song from your computer through your sound card to hard disk, or record from your CD player to a tape deck, but getting a digital copy of the music that is on the disc, and getting a good one--let alone a perfect one--is another story altogether.

WHY EXTRACTION?

There are many reasons to move audio from CDs to hard disk. Some would argue that the most common is for piracy purposes, although that debate is better left for another forum. Here we are just going to examine the process of Digital Audio Extraction, also known generally and unfortunately by the word "ripping."

Digital Audio Extraction (DAE) is the process of moving a Red Book track on a CD, usually music, from that CD to a hard drive or other storage medium by creating a file in any number of formats, although the most popular one is the WAV format. There are many possible purposes for which one might want to move the track into a file: to edit the sound, to rerecord it to another disc for a compilation disc, to further manipulate the file by compressing it into an MP3 file or a Yamaha VQ file, or to convert it to a lower-quality WAV file to use as a system sound, to name just a few.

Many CD recording software packages contain a digital audio extraction function. This functionality has been around as long as recording software. But only recently has it become so popular a feature that there are now many specialized programs that do nothing but extract audio. Recent years have seen many recording software manufacturers releasing new versions of their programs with enhanced audio features or producing separate or companion programs for audio extraction, manipulation, and recording.

LIKE PULLING TEETH?

Why is it so hard to get good extraction? The difficulties are inherent in the way audio discs are written. Data on an audio disc is organized into frames in order to ensure a constant read rate. Each frame consists of 24 bytes of user data, plus synchronization, error correction, and control and display bits. One of the first things that it is crucial to understand about CDs is that its data is not arranged in distinct physical units. Instead, the data in one frame is interleaved with the data in many other frames so that a scratch or defect in the disc will not destroy a single frame beyond correction. Rather, a scratch will destroy a small portion of many frames, all of which can probably be recovered.

A Red Book disc itself is divided into three areas: Lead In, Program, and Lead Out. Each track's location, or address, is recorded in the disc's Table of Contents (TOC), which is stored in the Lead In area of every disc. Because pressed CDs are read-only, the number and location of the audio tracks to be recorded are known in advance, and the final TOC is created on the glass master in advance of the actual audio data. An audio disc can contain up to 99 tracks, which are stored in the Program area. Following the Program area is the Lead Out area, which is simply 90 seconds of silence, or blank sectors. Encoding a Lead Out area on an audio disc lets CD-Audio players know that the music stream has ended.