All About the CD, HDCD, and SACD Audio Disc Formats
Aug 20, · Audio CDs are designed for one purpose: audio. They contain raw, uncompressed data, in a very fixed format If you’ve ever seen blank, minute CDs, these hold roughly megabytes of data – enough for about 70 minutes of sound in audio CD format. Data CDs, . Jun 15, · Therefore, the audio format used for CD audio tracks does not correlate directly to an computer audio file type. However, there are two file formats that are very similar to the CD audio format, since they support the same sampling rate and bit depth. These are the WAVE and AIFF formats. WAVE and AIFF are two audio formats that support KHz, bit, stereo audio, which is the standard .
Therefore, the audio format used for CD audio tracks does not correlate directly to an computer audio rormat type. However, there are two file formats that are very similar to the CD audio format, since they support the same sampling rate and bit depth.
These are the WAVE. AIF formats. They are also encoded with pulse code modulation PCMwhich is the same encoding used by CD audio tracks. Since the headers are stripped away when the audio data is converted to CD audio, both file types are a good choice for creating audio CDs.
This means you can copy the tracks to your hard drive by simply dragging them from the CD window to your desktop. In Windows, audio CD formqt show up as. CDA files. These are shortcuts to tracks on the CD, which iis not contain audio data.
Therefore, if you drag a CDA file to your desktop, it will only produce a shortcut. When the same Iis as above is inserted into a Windows computer, the following window appears. However, the quality may not be audi good, since the compressed format must be converted to an uncompressed format.
While the sound quality should not be any worse than the original compressed sound, it will not improve when converted to CD quality audio. However, it may not make much of a difference as long as you have high-quality compressed how to repair windows xp with command prompt pdf files.
With today's advanced audio compression algorithmsmost people cannot tell the difference between compressed and uncompressed audio files. Browse File Types.
Get the facts about audio CDs and related disc formats
Jan 06, · All About the CD, HDCD, and SACD Audio Disc Formats The Audio CD Format. CD stands for compact disc. Compact disc refers to both the disc and the digital audio playback SPARS Codes For CDs. AAD: The initial audio recording was made using analog recording equipment (such as an audio tape Other. Apr 25, · 16 bit Hz is CD quality audio. 16 bit Hz is Dvd quality audio. 16 bit Hz is Studio quality audio 16 bit Hz is studio quality. Basically the higher Hz range the more frequency ranges you can hear in clarity and sharpness, detail. of the song played from bass to treble to high pitched notes.
The standard is defined in the Red Book , one of a series of Rainbow Books named for their binding colors that contain the technical specifications for all CD formats. The format gained worldwide acceptance in —84, selling more than a million CD players in those two years, to play From the early s, CDs were increasingly being replaced by other forms of digital storage and distribution, with the result that by the number of audio CDs being sold in the U.
The optophone, first presented in , was an early device which used light for both recording and playback of sound signals on a transparent photograph. Russell has been credited with inventing the first system to record digital video on an optical transparent foil that is lit from behind by a high-power halogen lamp, not a laser.
Following litigation, Sony and Philips licensed Russell's patents for recording, not the play-back part then held by a Canadian company, Optical Recording Corp. The compact disc is an evolution of LaserDisc technology, where a focused laser beam is used that enables the high information density required for high-quality digital audio signals.
Unlike the prior art by Optophonie and James Russell, the information on the disc is read from a reflective layer using a laser as a light source through a protective substrate. Prototypes were developed by Philips and Sony independently in the late s. After their commercial release in , compact discs and their players were extremely popular. The unified design of the compact disc allowed consumers to purchase any disc or player from any company, and allowed the CD to dominate the at-home music market unchallenged.
In , Lou Ottens, director of the audio division of Philips , started a small group to develop an analog  optical audio disc with a diameter of 20 cm 7. The diameter of Philips's prototype compact disc was set at Heitaro Nakajima , who developed an early digital audio recorder within Japan's national public broadcasting organization NHK in , became general manager of Sony 's audio department in His team developed a digital PCM adaptor audio tape recorder using a Betamax video recorder in After this, in the leap to storing digital audio on an optical disc was easily made.
A year later, in September , Sony showed the press a 30 cm 12 in disc that could play an hour of digital audio 44, Hz sampling rate and bit resolution using MFM modulation. A week later, on 8 March, Philips publicly demonstrated a prototype of an optical digital audio disc at a press conference called "Philips Introduce Compact Disc"  in Eindhoven , Netherlands. In , Sony and Philips set up a joint task force of engineers to design a new digital audio disc. Led by engineers Kees Schouhamer Immink and Toshitada Doi , the research pushed forward laser and optical disc technology.
First published in , the standard was formally adopted by the IEC as an international standard in , with various amendments becoming part of the standard in Philips coined the term compact disc in line with another audio product, the Compact Cassette ,  and contributed the general manufacturing process , based on video LaserDisc technology.
Philips also contributed eight-to-fourteen modulation EFM , while Sony contributed the error-correction method, CIRC , which offers a certain resilience to defects such as scratches and fingerprints. The Compact Disc Story ,  told by a former member of the task force, gives background information on the many technical decisions made, including the choice of the sampling frequency, playing time, and disc diameter.
The task force consisted of around 6 persons,   though according to Philips, the compact disc was "invented collectively by a large group of people working as a team. Philips established the Polydor Pressing Operations plant in Langenhagen near Hannover , Germany , and quickly passed a series of milestones. As the price of players gradually came down, and with the introduction of the portable Discman the CD began to gain popularity in the larger popular and rock music markets.
With the rise in CD sales, pre-recorded cassette tape sales began to decline in the late s; CD sales overtook cassette sales in the early s. The first major artist to have their entire catalog converted to CD was David Bowie , whose first fourteen studio albums of then sixteen were made available by RCA Records in February , along with four greatest hits albums; his fifteenth and sixteenth albums had already been issued on CD by EMI Records in and , respectively.
Confronted with the instability of DACs, manufacturers initially turned to increasing the number of bits in the DAC and using several DACs per audio channel, averaging their output.
A breakthrough in the late s culminated in development of "1-bit" DAC , which converts high-resolution low-frequency digital input signal into a lower-resolution high-frequency signal that is mapped to voltages and then smoothed with an analog filter. The temporary use of a lower-resolution signal simplified circuit design and improved efficiency, which is why it became dominant in CD players starting from the early s.
The CD was primarily planned as the successor to the vinyl record for playing music, rather than as a data storage medium. However, CDs have grown to encompass other applications.
The lossless nature of digital audio caused an uproar in the taper community, which condemned the use of CDs for distributing concert bootlegs. CD sales in the United States peaked by With the advent and popularity of Internet-based distribution of files in lossily-compressed audio formats such as MP3 , sales of CDs began to decline in the s. The increasing popularity of solid-state media and music streaming services caused the replacement of automotive CD players in favor of minijack auxiliary inputs, wired connection to USB devices and wireless Bluetooth connection.
Despite the rapidly declining sales year-over-year, the pervasiveness of the technology remained for a time, with companies placing CDs in pharmacies, supermarkets, and filling station convenience stores targeting buyers least able to use Internet-based distribution.
Sony and Philips received praise for the development of the compact disc from professional organizations. These awards include. The Red Book specifies the physical parameters and properties of the CD, the optical parameters, deviations and error rate, modulation system eight-to-fourteen modulation , EFM and error correction facility cross-interleaved Reed—Solomon coding , CIRC , and the eight subcode channels. The standard also specifies the form of digital audio encoding 2-channel signed bit LPCM sampled at 44, Hz.
Although rarely used, the specification allows for discs to be mastered with a form of emphasis. The standard is not freely available and must be licensed. It is available from Philips and the IEC. The sampling rate is adapted from that attained when recording digital audio on videotape with a PCM adaptor , an earlier way of storing digital audio. In the end Sony won, so 16 bits and Philips found a way to produce bit quality using its bit DAC by using four times oversampling.
Some CDs are mastered with pre-emphasis , an artificial boost of high audio frequencies. The pre-emphasis improves the apparent signal-to-noise ratio by making better use of the channel's dynamic range. On playback, the player applies a de-emphasis filter to restore the frequency response curve to an overall flat one.
Playback of such discs in a computer or 'ripping' to wave files typically does not take into account the pre-emphasis, so such files play back with a distorted frequency response. The creators of the CD originally aimed at a playing time of 60 minutes with a disc diameter of mm Sony or mm Philips. According to a Sunday Tribune interview,  the story is slightly more involved. In , Philips owned PolyGram , one of the world's largest distributors of music. PolyGram had set up a large experimental CD plant in Hannover , Germany, which could produce huge numbers of CDs having a diameter of mm.
Sony did not yet have such a facility. If Sony had agreed on the mm disc, Philips would have had a significant competitive edge in the market.
The long playing time of Beethoven's Ninth Symphony imposed by Ohga was used to push Philips to accept mm, so that Philips' PolyGram lost its edge on disc fabrication. The minute playing time of a CD, which is longer than the 22 minutes per side   typical of long-playing LP vinyl albums , was often used to the CD's advantage during the early years when CDs and LPs vied for commercial sales.
CDs would often be released with one or more bonus tracks, enticing consumers to buy the CD for the extra material. However, attempts to combine double LPs onto one CD occasionally resulted in the opposite situation in which the CD would instead offer less audio than the LP.
The emergence of minute CDs allowed for some double albums that were previously edited for length or packaged as double-CDs to be re-released on a single disc, such as by Prince in the case of the former and Tommy by the Who in the case of the latter. Playing times beyond 74 minutes are achieved by decreasing track pitch the distance separating the track as it spirals the disc in violation of strict Red Book standards.
However, most players can still accommodate the more closely spaced data if it is still within Red Book tolerances. In current practice, maximum CD playing time has crept higher by reducing minimum engineering tolerances. The source audio data is divided into frames, containing twelve samples each six left and six right samples, alternating , for a total of bits 24 bytes of audio data per frame.
This stream of audio frames, as a whole, is then subjected to CIRC encoding, which segments and rearranges the data and expands it with error correction codes in a way that allows occasional read errors to be detected and corrected.
CIRC encoding interleaves the audio frames throughout the disc over several consecutive frames so that the information will be more resistant to burst errors. Therefore, a physical frame on the disc will actually contain information from multiple logical audio frames. This process adds 64 bits of error correction data to each frame.
After this, 8 bits of subcode or subchannel data are added to each of these encoded frames, which is used for control and addressing when playing the CD. CIRC encoding plus the subcode byte generate bytes long frames, called "channel-data" frames.
These frames are then modulated through eight-to-fourteen modulation EFM , where each 8-bit word is replaced with a corresponding bit word designed to reduce the number of transitions between 0 and 1. This reduces the density of physical pits on the disc and provides an additional degree of error tolerance. Three "merging" bits are added before each bit word for disambiguation and synchronization.
A bit word a bit pattern plus 3 merging bits is added to the beginning of each frame to assist with synchronization, so the reading device can locate frames easily. With this, a frame ends up containing bits of "channel data" which are decoded to only bits music.
The frames of channel data are finally written to disc physically in the form of pits and lands , with each pit or land representing a series of zeroes, and with the transition points—the edge of each pit—representing 1.
A Red Book-compatible CD-R has pit-and-land-shaped spots on a layer of organic dye instead of actual pits and lands; a laser creates the spots by altering the reflective properties of the dye.
Due to the weaker error correction sector structure used on audio CDs and video CDs Mode 2 Form 2 than on data discs Mode 1 or Mode 2 Form 1 , C2 errors are not correctable and signify data loss. The audio data stream in an audio CD is continuous, but has three parts.
The main portion, which is further divided into playable audio tracks, is the program area. This section is preceded by a lead-in track and followed by a lead-out track. The lead-in and lead-out tracks encode only silent audio, but all three sections contain subcode data streams.
The lead-in's subcode contains repeated copies of the disc's Table of Contents TOC , which provides an index of the start positions of the tracks in the program area and lead-out.
The track positions are referenced by absolute timecode , relative to the start of the program area, in MSF format: minutes, seconds, and fractional seconds called frames. Each timecode frame is one seventy-fifth of a second, and corresponds to a block of 98 channel-data frames—ultimately, a block of pairs of left and right audio samples. Timecode contained in the subchannel data allows the reading device to locate the region of the disc that corresponds to the timecode in the TOC. The TOC on discs is analogous to the partition table on hard drives.
The largest entity on a CD is called a track. A CD can contain up to 99 tracks including a data track for mixed mode discs. Each track can in turn have up to indexes, though players which handle this feature are rare. The vast majority of songs are recorded under index 1, with the pre-gap being index 0.
Sometimes hidden tracks are placed at the end of the last track of the disc, often using index 2 or 3. This is also the case with some discs offering " sound effects", with and being indexed as two and three on track The index, if used, is occasionally put on the track listing as a decimal part of the track number, such as The track and index structure of the CD were carried forward to the DVD format as title and chapter, respectively.
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