| Media type | Optical disc |
|---|---|
| Capacity | Typically up to 700 MB |
| Read mechanism | 780 nm wavelength semiconductor laser |
| Developed by | Pacific Microsonics Inc./Microsoft |
| Usage | Audio storage |
| Extended from | Redbook |
High Definition Compatible Digital, or HDCD is a patented encode-decode process, now owned by Microsoft, that improves the audio quality of standard Redbook audio CDs, while retaining backward compatibility with existing Compact disc players. At over 5,000 titles,[1] HDCD-encoded releases constitute a fraction of the total CD commercial music catalog.
A number of universal CD and DVD players include HDCD decoding, and version 9 and above of the Windows Media Player software (on personal computers with a 24-bit sound card) are capable of decoding HDCD.
An HDCD-encoded CD usually, but not always, has the HDCD logo printed on the back cover. An HDCD logo may also be displayed in Windows Media Player 9 or above when an HDCD encoded disc is played.
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HDCD encodes the equivalent of 20 bits worth of data in a 16-bit digital audio signal by using custom dithering, audio filters, and some reversible amplitude and gain encoding; Peak Extend, which is a reversible soft limiter and Low Level Range Extend, which is a reversible gain on low-level signals. There is thus a benefit at the expense of a very minor increase in noise.[2][3]
HDCD encoding places a control signal in the least-significant bit of a small subset of the 16-bit Red Book audio samples (a technique known as in-band signaling). The HDCD decoder in the consumer's CD / DVD player, or in some cases audio receiver, if present, responds to the signal. If no decoder is present, the disc will be played as a regular CD.
In itself, the use of the first bit in the dithered least-significant bit stream will degrade the sound quality on a non-HDCD player by decreasing the signal-to-noise ratio but only by a minuscule amount. HDCD Peak Extension, if chosen in HDCD mastering, will apply compression to the peaks which will be audible in playback on a non-HDCD system which does not apply the appropriate expansion curve.
HDCD provides several digital features, which the audio mastering engineer controls at his/her own discretion. They include
HDCD technology was developed between 1986 and 1991 by "Professor" Keith O. Johnson and Michael "Pflash" Pflaumer of Pacific Microsonics Inc. It was made publicly available as HDCD-enabled audio CDs in 1995.
In 2000, Microsoft acquired the company and all of its intellectual property assets.[4][5]
There have been a number of players and processors over the years that were capable of properly decoding the information from HDCDs. Included were those from Spectral (USA), California Audio Labs (USA), Mark Levinson/Madrigal (USA), Arcam (UK), Burmester (Germany), Cary (USA), Naim (UK), Linn (UK), Classe (Canada), A&R Cambridge Ltd (ARCAM) (UK), Denon (Japan), Rotel (Japan) and Cayin-Spark (China) plus all the OPPO universal players. Outboard DACs (digital to analog converters) were produced by Berkeley Audio Design, Spectral, Classe, Mark Levinson, and others.
In 1998, Burr-Brown (now part of Texas Instruments) and Sanyo Electronics of Japan introduced low cost D to A converters with HDCD decoding included, allowing HDCD to be used in CD and DVD players in the $100 range. HDCD algorithms were included in DVD chips from many IC makers including Motorola and C-Cubed, allowing HDCD to be offered by mass-market DVD player makers such as Panasonic and Toshiba. As of 2007, a number of players continue to feature HDCD capability, including Harman Kardon, Denon, Marantz, Cary, Rotel, Mark Levinson, Shanling, NAD, Spectral. More recently the Oppo line of players all feature HDCD decoding.
There are no labels that record and release only HDCDs. Reference Recordings has produced many classical CDs in the HDCD format, which include new releases and have won numerous awards. Linn Records has a number of hybrid HDCD / SACDs, and also seem to enjoy a good reputation among music enthusiasts.
As for "mainstream" popular artists, Laurie Anderson, Lifehouse, John Mellencamp, Lee Ann Womack, Tool, The Beach Boys, Beck, The Grateful Dead, Jerry Garcia, Madonna, Mark Knopfler, King Crimson, Roxy Music (also Bryan Ferry), Van Halen, Joni Mitchell, Neil Young, Mannheim Steamroller, Kenny Chesney, Dixie Chicks, The B-52's, NOFX, Da Brat, Natalie Merchant, Lucinda Williams, and Mike Oldfield have released albums on HDCD. As of January 2007, there are roughly the same number of titles released on SACD as on HDCD-encoded CDs.
Since Windows Media Player 9 for Windows XP, PCs are capable of decoding and playing HDCDs on personal computers with a 24-bit sound card installed.[6][7] Media Player 9 indicates the presence of an HDCD by flashing the logo in the control bar at the bottom of the application window. This was changed in versions 10 and 11; if an HDCD is inserted into a drive with WMP 10/11 running, the HDCD logo appears only if the HDCD feature is disabled, thus, signalling that it should be enabled for proper decoding.
This feature must be enabled by changing a WMP speakers setting involving 24-bit audio. The path to this setting is found in the Player's Options control panel which can be accessed from the Tools menu: Tools/Options/Devices/Speakers/Properties/Performance.[8]
Due to player design, the HDCD decoding is placed within the CD read chain. Thus, HDCD decoding can only be achieved whilst directly playing back HDCD-formatted disks. The Windows Media Player software is not currently able to decode HDCD information present from ripped images of disks. However, Media Player 9 is able to recognize copies of HDCDs.[9]
Windows Media Player does not decode HDCD audio streams during ripping and the decoded encoded extra HDCD information is lost (but the information is maintained provided the data is stored in a lossless format). By using a WAV output recorded plugin, it is possible to grab a perfect digital copy of a decoded HDCD stream, which can then be used for encoding into other formats.
In some HDCD discs, and some DVD players using WMP, the first track is not recognized as HDCD but all other tracks are, ("if played a few seconds early or a few seconds before the actual song") at the end of the previous track, that is because HDCD has a control signal, if that control signal is not detected by WMP at the beginning of the song, the HDCD decoder is not activated.
A member of the Doom9 forum has authored a Windows CLI utility, hdcd.exe, to extract and decode the HDCD data in 16-bit WAV files ripped from HDCD discs. This utility writes a 24-bit WAV output files with four bits of padding per sample. The author of the utility decided not to make the source code publicly available as the HDCD technology is patented.[10]
Illustrate's dBpoweramp Music Converter, a Windows GUI program, has an HDCD DSP effect that acts as a front-end to the utility listed above.[11]
A plugin[12] is available for foobar2000 that will decode HDCD data in any 16-bit PCM passed through it, resulting in a 20-bit PCM stream.