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.
Launched in 2004, The Fujifilm PhotoDisc CD-R is essentially a standard CD-R disc with a black substrate layer that claims to protect the data from ultra-violet and solar radiation. It also uses a different dye (phthalocyanine rather than the usual cyanine) in the recording layer, which should offer more resistance to heat and sunlight.
Although they are reported to be very reliable, for archival purposes gold archival CD-R discs are probably better.
Despite the name, the discs can be used for any purpose that a standard CD-R can be used for, and don’t just store photos.
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.
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.
Photo CD was an optical disc system based on the Compact Disc that allowed the storage of up to 100 high quality images in a proprietary format. It was introduced by Kodak in 1992, and the format is defined in the Biege Book standard (one of the Rainbow Books covering Compact Disc standards). Kodak’s Photo CD system also included the scanners for photo processing labs that could take scans from film negatives or slides. Photographers could take exposed film to a Photo CD processing lab, where the film would be developed and scanned to a Photo CD, or they could have previously developed film scanned to Photo CD.
Photo CDs were designed to be played on a dedicated standalone Photo CD player connected to a domestic television, but they could also be played in a CD-i player. It was possible to play them on a computer with suitable software, but at the time CD-ROM drives were still uncommon.
The system was not popular with consumers, though it was more accepted by professional photographers. Although there were around 140 Photo CD processing labs in the US alone by 2000, by this time domestic scanners enabled consumers to scan their own photographs. In 1999, Kodak had also introduced the more affordable Picture CD system, with images in JPEG format burned onto a recordable CD that also held the software required to the view and edit the images on a computer.
Kodak had completely abandoned the Photo CD business by 2004, but never released the image specifications. However, it has been reverse-engineered so it is possible to convert images to other formats.
XRCD (eXtended Resolution Compact Disc) was introduced by JVC in 1995. XRCD discs conform to Red Book standards and will play on any Compact Disc player, but claim to use much higher quality mastering and manufacturing processes to produce a sound as close as possible to the original master tape.
Subsequent versions of XRCD are called XRCD2 and XRCD24.
All versions of XRCD disc are encoded at 16 bits; the 24 in XRCD24 refers to the use of 24 bit encoding when digitising the original analogue source (XRCD and XRCD2 used 20 bit encoding of the original source).
CD-i Digital Video was a short-lived video disc format introduced by Philips in 1993 that was designed to be played in CD-i players equipped with an optional Digital Video Cartridge. This expansion unit contained a 32 bit RISC processor and 1 MB of RAM to provide MPEG-1 decoding.
CD-i Digital Video followed the Green Book standard for CD-i discs, making it incompatible with the Video CD format introduced shortly afterwards that followed the White Book standard. However, whilst Video CD players could not play CD-i Digital Video, CD-i players with the optional Digital Video Cartridge could play both formats. Some other CD-i discs such as games also made use of the Digital Video Cartridge to play video.
One of the two differences between the formats was the resolution, that was slightly higher on CD-i Digital Video (384×288 instead of 352×288 for Video CD). When a Video CD is played on a CD-i player, slightly larger pixels are displayed to fill the screen.
Only around 20 movies were released on CD-i Digital Video before Philips switched to Video CD for distributing movies in 1994.
Mini CD-R (CD-Recordable) and Mini CD-RW (CD-Rewritable) are 8cm versions of CD-R/CD-RW. They can hold anything from 156 MB (18 minutes of music) to 210 MB (24 minutes of music).
They can be written to in spindle-based or tray-loading CD-R / CD-RW burners (and read in spindle-based or tray-loading Compact Disc players) but there were also some devices that were specifically designed around the Mini CD-R/CD-RW.
One of these was a number of models in the Sony Mavica line of digital cameras. The first of these was the MVC-CD1000 released in 2000, which could record to Mini CD-Rs. Later models in the line (the last of which was released in 2003) could use either Mini CD-R or Mini CD-RW.
There was also a portable Mini CD-R burner called the Imation RipGo! that was introduced in 2001. This could burn MP3 files to disc, and also play them back. Sony also introduced a Mini CD burner (called the PhotoVault), allowing pictures to be saved from a Memory Stick, USB flash drive, or camera with a USB connection.