The Audio CD Format
CD stands for compact disc. Compact disc refers to both the disc and the digital audio playback format developed by Philips and Sony. The format refers to audio that is digitally encoded like computer data (1s and 0s) into pits on a disc through a process called PCM. PCM is a mathematical representation of audio and music in digital form. The first CD recordings were manufactured in Germany on August 17, 1982. The title of the first full CD test recording was Richard Strauss’ Alpine Symphony. Later that year, on October 1, 1982, CD players became available in the U.S. and Japan. The first CD sold was in Japan—Billy Joel’s 52nd Street, previously released on vinyl in 1978. The CD started the digital revolution in audio, PC gaming, and PC storage applications. It also contributed to the development of the DVD. Sony and Philips jointly hold the patents on the development of the CD and CD player technology. From its debut until about 1995, pre-recorded CDs included special codes (referred to as SPARS codes) on the packaging. These codes informed consumers about the recording, mixing, and mastering process used to make that specific CD. You may still have this labeling on some of the CDs that you own.
SPARS Codes For CDs
The SPARS codes for CDs were:
AAD: The initial audio recording was made using analog recording equipment (such as an audio tape recorder). The mixing was also done using analog equipment, and the final mastering was done digitally.ADD: The initial audio recording was made using analog recording equipment (such as an audio tape recorder). The mixing was done digitally, and the final mastering was done digitally.DDD: All stages, from the initial recording to the final mastering, was done digitally.
Other Uses for CDs
In addition to pre-recorded audio, CDs can also be used in several other applications:
CD-R: CD-R stands for CD-Recordable. These discs can be used to record or burn music or data using a CD recorder (music only) or a PC (music or data). Some CD-Rs are designated for music recording only, and others can record both music or data. CD-Rs can only be recorded once. CD-RW: The same capabilities as a CD-R, except that the CD can be erased and used over again. The RW designation means re-writable. CD-TEXT: This an audio CD variation that provides text information on the disc in addition to music. This may include things such as the disc table of contents, track titles, artist, and in some cases, lyrics and genre. On CD players, the text information is shown on the player’s status display, if it has one. Also, if the CD is played on a DVD or Blu-ray Disc player, in most cases, the information may be displayed on a TV screen. MP3-CD: An MP3 CD can be a CD-R or RW disc that MP3 music files are recorded on, instead of standard CD audio files. These discs can be played on most CD, DVD, and Blu-ray Disc players. JPEG Photo CD: A JPEG Photo CD can be either a CD-R or RW disc that has photos on it recorded in the JPEG file format. JPEG Photo CDs can be played on PCs and compatible CD, DVD, and Blu-ray Disc players. VideoCD: In addition to audio and photos, you can record video on a CD. This is not the same as a DVD, with the quality being between the VHS and DVD formats. Also, video CDs aren’t playable on CD players unless the CD player has a video output connection, which isn’t likely. VideoCDs are playable on compatible DVD and Blu-ray Disc players. CD Graphics: This rare variation of the CD format includes basic graphics that can be read by a compatible player with a video output for display on a TV or video projection screen. This capability is primarily used to display song lyrics for karaoke applications. This feature may be labeled CD+G, CD-G, CD+Graphics, CD-Extended Graphics, or TV-Graphics.
High Definition Compact Disc (HDCD)
HDCD is a variation of the CD audio standard that extends the audio information stored in the CD signal by 4 bits (CDs are based on 16-bit audio technology) to 20 bits. HDCD can extend the sonic capacity of current CD technology to new standards but still enable HDCD encoded CDs to be played on non-HDCD CD players without increasing the CD software price. Also, as a by-product of more precise filtering circuitry in HDCD chips, even regular CDs sound fuller and more natural on an HDCD-equipped CD player. When buying music CDs, look for the HDCD initials on the back or internal packaging. Many releases may not include the HDCD label but may still be HDCD discs. If you have a CD player that features HDCD decoding, it automatically detects it and provides the added benefits.
Super Audio Compact Disc (SACD)
SACD (Super Audio Compact Disc) is a high-resolution audio disc format developed by Sony and Philips. Using the Direct Stream Digital (DSD) file format, SACD provides an alternative to Pulse Code Modulation (PCM) used in the CD format. While the standard CD format is tied to a 44.1 kHz sampling rate, SACD samples at 2.8224 MHz. Also, instead of a 16-bit depth, it uses a 1-bit depth. With a storage capacity of 4.7 gigabytes per disk (as much as a DVD), SACD can accommodate separate stereo and six-channel mixes of 100 minutes each. The SACD format can also display photo and text information, such as liner notes. Still, this feature isn’t incorporated into most discs.
Check Your CD Player For Compatibility
CD players can’t play SACDs, but SACD players are backward compatible with conventional CDs. Some SACD disks are dual-layer discs with PCM content that can be played on standard CD players. In other words, the same disk can hold both a CD and an SACD version of recorded content. That means you can invest in dual-format SACDs to play on your current CD player and then access the SACD content on the same disc later on an SACD-compatible player. Not all SACD discs have a standard CD layer. This means you have to check the disc label to see if a specific SACD disc can play on a standard CD player. SACDs come in either two-channel or multi-channel versions. In cases when an SACD also has a CD version on the disc, the CD will always be two-channel, but the SACD layer may be either a two or multi-channel version. The DSD file format coding used in SACDs is also used as one of the available formats for Hi-Res audio downloads. This offers music listeners enhanced quality in a non-physical audio disc format. DSD-encoded music files can be downloaded from services such as HD Tracks, HighResAudio, Native DSD, ProStudio Masters, and Super HiRez. Files can be saved to PCs and saved to storage media such as a hard drive or USB flash drive.
