Electronic skip protection
Encyclopedia
Electronic skip protection is a memory buffer
system used mainly in some portable Compact Disc
(CD) players and all MiniDisc
(MD) units.
and the content is buffered (with optional ADPCM compression) and fed to RAM
within the player. The audio content is read from RAM, optionally decompressed, and then sent to the amplifier
. When the disc reading is interrupted, the player momentarily reads the data stored in RAM while the tracking circuitry finds the passage prior to the interruption on the CD.
Another method has the disc rotating at variable or CLV
speed (the normal rotation method for a CD player), but at a slightly higher speed than with the buffer feature switched off. The buffer method is the same as before.
When first introduced, 3 seconds was the maximum buffering time. As of 2006 times range from 10 seconds to "skip-free," where the player will rarely skip.
Due to the nature of the ATRAC
compression scheme, and to ensure uninterrupted playback in the presence of fragmentation, all MD
decks and portables buffered at least 10 seconds when the format was introduced in 1995. As of 2006, MD units have much bigger buffers.
The advent of flash
-based MP3 players has eliminated the need for expensive anti-shock RAM chips.
), etc.
Memory buffer register
A Memory Buffer Register is the register in a computer's processor, or central processing unit, CPU, that stores the data being transferred to and from the immediate access store. It acts as a buffer allowing the processor and memory units to act independently without being affected by minor...
system used mainly in some portable Compact Disc
Compact Disc
The Compact Disc is an optical disc used to store digital data. It was originally developed to store and playback sound recordings exclusively, but later expanded to encompass data storage , write-once audio and data storage , rewritable media , Video Compact Discs , Super Video Compact Discs ,...
(CD) players and all MiniDisc
MiniDisc
The disc is permanently housed in a cartridge with a sliding door, similar to the casing of a 3.5" floppy disk. This shutter is opened automatically by a mechanism upon insertion. The audio discs can either be recordable or premastered. Recordable MiniDiscs use a magneto-optical system to record...
(MD) units.
Technology
When the buffering circuitry is in operation, the compact disc is read at a fixed read speed or CAVConstant angular velocity
In optical storage, constant angular velocity is a qualifier for the rated speed of an optical disc drive, and may also be applied to the writing speed of recordable discs...
and the content is buffered (with optional ADPCM compression) and fed to RAM
Ram
-Animals:*Ram, an uncastrated male sheep*Ram cichlid, a species of freshwater fish endemic to Colombia and Venezuela-Military:*Battering ram*Ramming, a military tactic in which one vehicle runs into another...
within the player. The audio content is read from RAM, optionally decompressed, and then sent to the amplifier
Amplifier
Generally, an amplifier or simply amp, is a device for increasing the power of a signal.In popular use, the term usually describes an electronic amplifier, in which the input "signal" is usually a voltage or a current. In audio applications, amplifiers drive the loudspeakers used in PA systems to...
. When the disc reading is interrupted, the player momentarily reads the data stored in RAM while the tracking circuitry finds the passage prior to the interruption on the CD.
Another method has the disc rotating at variable or CLV
Constant linear velocity
In optical storage, constant linear velocity is a qualifier for the rated speed of an optical disc drive, and may also be applied to the writing speed of recordable discs. CLV implies that the angular velocity varies during an operation, as contrasted with CAV modes...
speed (the normal rotation method for a CD player), but at a slightly higher speed than with the buffer feature switched off. The buffer method is the same as before.
History
The technology surfaced around 1995 as a physically smaller alternative to the bulky rubber shock absorbers utilized in portable players at the time. It much reduced the size of the hitherto bulky players designed for use in moving cars, in particular. Small rubber shock absorbers are still used, but are less effective than the bigger pre-1995 ones.When first introduced, 3 seconds was the maximum buffering time. As of 2006 times range from 10 seconds to "skip-free," where the player will rarely skip.
Due to the nature of the ATRAC
ATRAC
Adaptive Transform Acoustic Coding is a family of proprietary audio compression algorithms developed by Sony. MiniDisc was the first commercial product to incorporate ATRAC in 1992. ATRAC allowed a relatively small disc like MiniDisc to have the same running time as CD while storing audio...
compression scheme, and to ensure uninterrupted playback in the presence of fragmentation, all MD
MiniDisc
The disc is permanently housed in a cartridge with a sliding door, similar to the casing of a 3.5" floppy disk. This shutter is opened automatically by a mechanism upon insertion. The audio discs can either be recordable or premastered. Recordable MiniDiscs use a magneto-optical system to record...
decks and portables buffered at least 10 seconds when the format was introduced in 1995. As of 2006, MD units have much bigger buffers.
The advent of flash
Flash memory
Flash memory is a non-volatile computer storage chip that can be electrically erased and reprogrammed. It was developed from EEPROM and must be erased in fairly large blocks before these can be rewritten with new data...
-based MP3 players has eliminated the need for expensive anti-shock RAM chips.
Cons
- Audio quality may be slightly worsened due to compression artifacts when the system is in use. Quality is improved with uncompressed buffering.
- Battery life is shortened due to the fixed (CAV) read speed of the disc and power required by the memory.
- Older players (1992-1997) had at most half the battery life when the skip protection system was in use.
- Players from 1997 have more power-efficient skip protection.
- Portable players, more so portable CD players but also some portable DVD players, that invariably include an ASP feature (Anti-Skip-protection), struggle with CD-R/RW , DVD-R/RW and DVD+R/RW discs - due to the ASP feature being enabled. This is due to the limited read capability of such write-yourself media discs over retail pressed discs. It is widely believed that the buffer system of the ASP feature conflicts with the limited read capability of such discs. This conflict affects the re-writable formats more so than the write once formats, but can be prevalent with both. It is therefore advisable that if you use write-yourself media often, to look for a portable player that allows ASP to be enabled/disabled. As such read issues are invariably non-existent when the ASP feature is disabled. Using slow burning speeds and high-quality media also helps.
Trade Names
"ESP", "Anti-Skip", "Anti-Shock", "Joggable" "G-Shock Protection" (Used by SonySony
, commonly referred to as Sony, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan and the world's fifth largest media conglomerate measured by revenues....
), etc.