The DTS 5.1 Music Disc was a Compact Disc format offering surround sound audio, usually in the 5.1 configuration. The discs conformed to Red Book standard, so could be played in a standard CD player, but without the use of a DTS decoder all that would be heard is white noise. The potential confusion between DTS 5.1 Music Discs and standard Compact Discs meant some retailers were reluctant to stock them. There is some compression applied to the audio, so sound quality is arguably slightly lower than a standard CD.
Formats such as DVD-Audio and Super Audio CD, launched a few years later, could also offer surround sound and meant an end to the DTS 5.1 Music Disc, though several hundred titles were released on the format.
DTS surround sound technology is also used in movie theatres, on DVD-Video and on Blu-ray. It was also used on a small number of LaserDiscs.
QSound is an audio processing system introduced by QSound Labs. It was applied at the sound mixing stage and attempts to produce a surround sound effect from a stereophonic source. It was used on around 65 Compact Disc albums from 1991 to around 2001, which display the QSound logo. The first album to use QSound was Madonna’s ‘The Immaculate Collection’ and all the tracks were either re-mixed or mixed using the system.
No additional equipment was necessary to play a QSound Compact Disc, and the discs comply fully with Red Book standards.
As well as Compact Disc albums, the QSound technology was also applied to computer game audio, television programmes and film soundtracks.
On mono devices, music mixed using the QSound system can have elements missing.
UHQCD is a type of audio Compact Disc introduced by Memory-Tech in Japan in 2015, and is a development of the HQCD (High Quality Compact Disc) introduced six years previously. UHQCD discs conform to Red Book standards and are playable in any audio CD player. They don’t contain any more audio information than a standard CD, but it is claimed that a higher-quality manufacturing process and higher quality materials in the reflective layer produces higher precision audio reproduction.
A photopolymer is used instead of standard polycarbonate, since in their liquid state photopolymers achieve better replication of the pits on the CD stamper.
As of 2017, there were over 900 titles available on UHQCD.
The Blu-spec CD was introduced in 2008 by Sony, and is a Red Book-compliant audio Compact Disc, so is playable on all audio Compact Disc players. Sony launched with 60 titles on Blu-spec CD.
Its name is derived from the shorter-wavelength blue laser used to create the master copy, which is claimed to produced more precise pits to reduce distortion due to reading errors, along with a new polymer polycarbonate developed for the Blu-ray Disc.
In 2012, a newer version called Blu-spec CD2 (or BSCD2) was introduced that claimed to have a more precise cutting machine and master discs made from silicon wafers. Sony called it Phase Transition Mastering.
Due to existing limitations of Compact Disc Digital Audio, it is debatable whether Blu-spec CDs offer better sound quality as there is no extra information stored on the disc.
As of 2017, new titles are still being released on both formats.
Minimax Compact Discs are generally CD singles which consist of a 3-inch playing area (equivalent to the mini CD single) surrounded by an area of translucent plastic (either clear or coloured) to make them full-size Compact Discs. The playable part of the disc conforms to Red Book standards.
On a normal Compact Disc, the reflective layer would continue to the edge of the disc, even if there was not enough music to fill it.
Because of the small playing area, minimax CDs can only hold a limited playing time (about 24 minutes maximum) and so have only been used for music singles or EPs.
They are very uncommon, presumably because of the extra expense in manufacturing them over a standard 5-inch CD single, but have been used for special edition singles, in much the same way as coloured vinyl records. It could be argued that the holographic CD is a form of minimax CD, as it is also formed of a mini CD single inside a larger area of plastic containing the holographic design.
The original specification for Compact Disc Digital Audio, known as the Red Book, did not make any provision for copy protection, and by the late 1990s millions of ripped audio tracks from Compact Discs were compressed as MP3s and shared over the internet.
The music industry did several things to try and rectify the situation, including setting up online music stores selling music through a subscription model, and the Recording Industry Association of America also prosecuted over 20,000 individuals they accused of sharing pirated MP3s.
Starting around 2000, the music industry also began to put copy-protection onto audio Compact Discs. Companies such as EMI, Sony, BMG, and for a time Warner used copy protection as a means to prevent ripping of audio tracks onto a computer.
Since the discs were non-compliant with the Red Book standard, they were not supposed to display the Compact Disc Digital Audio logo on either the disc or inside the jewel case. There was also a consumer outcry against the disks as they prevented tracks from being copied to the purchaser’s personal audio devices, and some CD players such as those in cars would not play the disks (since these sometimes used some CD-ROM components, especially if they were intended to play disks containing MP3 or other types of compressed files).
In 2005, it was discovered that Sony BMG were using a type of copy protection called Extended Copy Protection (XCP) which installed a rootkit on a user’s computer. This sparked a scandal as it could be used by malware, and Sony announced a recall of disks using XCP and suspended its use.
EMI was the last major label to abandon copy protection in 2006.
CD Cardz were introduced in 2000 by Serious Global Ltd of the UK, and consisted of trading card-sized CD-ROMs containing information about a character or sportsperson. They were also sold in the US by Serious USA.
CD Cardz were produced for popular shows such as Buffy the Vampire Slayer, Stargate SG-1, and films such as Final Fantasy, Lord of the Rings and Jurassic Park. The cards contained features such as screensavers, photos, trailers and biographies, and had a picture of the character printed on the disc. There were some sports-related card sets produced for EURO 2000, NBA and NFL, as well as Manchester United and Arsenal Football Clubs.
Like the similar business card CD-ROM, they did not work in slot-loading drives. CD Cardz had a capacity of 80 MB.
The CD Cardz format also appears to have been used to create interactive gift cards.
Serious appears to stopped producing CD Cardz and the later DVD Cardz in 2009 as the website ceased to exist by 2010.
Shaped Compact Discs first appeared in the mid-1990s, the first being The Flaming Lips Compact Disc single entitled ‘This Here Giraffe’ released in 1996 on a 8-pointed star-shaped disc.
The most common form of shaped Compact Disc is the business card sized CD-ROM introduced in 1998, but shaped CDs can come in a variety of shapes. Generally, Compact Disc audio discs can be symmetric or asymmetric, whereas shaped CD-ROMs are generally symmetrical so they do not cause vibrations in high-speed CD-ROM drives.
Shaped CDs contain less audio or data than standard 12cm discs, and may not work in all drives.
An enhanced CD (or ECD) is a Compact Disc that contains both audio content playable on a standard CD audio player, and multimedia content playable on a computer CD-ROM.
Introduced in 1994, the idea behind enhanced CDs was to offer the music buyer some extra bonus features using space on the disc that was unfilled by the music. This might take the form of music videos (similar to the earlier idea of CD Video), interviews, wallpapers, pictures, lyrics, or links to an artists website.
Rather confusingly, there were three different ways on combining the different content on the disc. Prior to 1996, enhanced CDs were created in one of two ways. One was to have the multimedia content in the first track, but this meant that track 1 needed to be skipped when played in a standard CD audio player or else the multimedia track could cause an unpleasant noise to be heard. A subsequent solution was to have the multimedia content in the pre-gap before track 1 (rather like the way a CD-i Ready disc worked). Both of these methods were known as ‘mixed-mode’, combining Red Book Digital Audio and Yellow Book CD-ROM information in a single ‘session’ on the same disc.
To get around the problems of mixed-mode discs, Philips and Sony released the Blue Book standards in 1995, and worked with Apple, Microsoft and the Recording Industry Association of America (RIAA) to develop them. This new standard specified multisession technology that used two sessions on the disc, the first one containing audio tracks, and the second one containing data that is invisible to CD audio players. In 1996, most enhanced CDs used mixed-mode with the multimedia in the pre-gap, but by 1997 most were using Blue Book standards. The only downside to the newer multisession technology was that CD-ROM drives made before 1996 might not recognise them if they were not multisession capable.
Enhanced CDs can usually be recognised the official ‘Enhanced CD’ logo recommended by the RIAA. They may also have the CD EXTRA logo (previously known as CD Plus), which was trademarked by Sony for use on Blue Book discs.
Later technologies like DVD-Audio or DualDisc tried to perform the same function of offering the music album with bonus material such as videos, but later albums often came instead with the videos on a separate DVD-Video.
CD-i Ready was a hybrid optical disc format, combining audio tracks readable by any Compact Disc audio player, and multimedia or interactive elements readable on a CD-i (Compact Disc Interactive) player. It was introduced by Philips in 1991.
The audio tracks conform to Red Book Compact Disc Digital Audio standards, while the CD-i part conforms to Green Book standards, and could contain interviews, photos, biographies, games and more. The CD-i component is located in the ‘pre-gap’ area before track 1, which is skipped over by Compact Disc audio players.
The idea, like CD-i generally, was not a commercial success, and there appear to be fewer than 20 titles released as CD-i Ready discs.
The ideas behind the hybrid CD-i Ready discs were used in later types of hybrid audio/data discs such as the Enhanced CD that contained content which could be read on a standard computer CD-ROM drive rather than requiring a dedicated CD-i player.