Creating Audio CD's

In Depth Tutorial

Background

Sound is our brain's interpretation of changes in air pressure against our eardrums. Audio recording as pioneered by Thomas Edison created a variety of devices which essentially duplicated the vibrations of our eardrums by engraving bumpy grooves on wax drums or wire. Playback was then accomplished by following the grooves with a "needle" that vibrated a membrane which in turn created a sound that approximated the original . Although the process was improved as other media such as ivory and eventually vinyl records were produced, the underlining principal was unchanged.

Digital sound, like  a computer program, is nothing more than a series of ones and zeros in  sequences that can be interpreted by a computer as instructions. These sound files can be stored on magnetic media such as a hard drive or floppy disk or on optical media such as compact disks, better known today as CD's.  Originally called CD-ROM to indicate that they were a Read Only Medium, CD's are now a read and write medium which is the actual purpose behind this piece.

There are some obvious similarities between vinyl records and CD's insofar as they are plastic disks with microscopic grooves or pits but the similarities stop there.  Unlike the grooves in records which are actual miniature sound vibrations, the pits in CD's represent ones and zeros. Unlike records that are played with a needle that follows the grooves, a CD is read with  tiny laser beams that can be aimed anywhere in any sequence.

In addition to data that a computer can interpret into sound, an audio file must contain additional computer instructions to enable error checking, decompression and other essential or ancillary information. Generally speaking the non-audio data is stored in the file header itself or in a special location on the CD.

Compact disk technology has not changed dramatically since the inception of the medium but there has been a revolution in access to the technology and in the content itself. Originally a CD was inserted into a stand alone CD player to play music; then a bit later CD's began to be used as a substitute for floppy disks to store computer installation programs. At this point in technological history there was a data CD and a music CD. A computer with a sound card could play a music CD but a data CD meant nothing to a CD player.

With the advent of new, more efficient compression algorithms new file types such as MP-3 were created while at the same time CD burners became affordable. The inevitable result was that computer users began to burn MP-3 files onto CD's so that we now had a music CD that couldn't be played by a CD player.

Add to the confusion more sound file formats, MP-3 players, combination players, DVD players, CD-R, CD-RW, multi-session, single-session and who knows what next. For the purpose of simplicity herein we'll call any optical disk that will play sounds through any device a music CD and any optical disk that can only be read by a computer a data CD. We'll still have to address some hybrids of course but it should make things easier to understand.

The various standards for CD-ROM are differentiated by book color. Book color is often used by standards committees to distinguish between topics. The first popularly know example was probably the Blue Book that was used by the automotive industry to establish standard resale values for used cars. The original CD-ROM standard for digital audio CD was called red book CD-DA standard.

Next, let's examine the original Redbook CD Digital Audio concept a bit deeper.