Electronic skip protection
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Electronic skip protection is a data buffer system used in some portable compact disc (CD) players and all MiniDisc (MD) units so that audio would not skip while the disk could not be read due to movement.
When the buffering circuitry is in operation, the compact disc is read at a fixed read speed or CAV 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 digital-to-analog converter. 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.
The technology surfaced around 1995 as a physically smaller alternative to the bulky rubber shock absorbers utilized in portable players at the time. It 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 larger pre-1995 ones.
When first introduced, 3 seconds was the maximum buffering time. In 2006, the time generally ranged 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 1992. As of 2006[update], MD units have much bigger buffers.
- Interruption-free performance.
- 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 onward 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.
"ESP", "Anti-Skip", "Anti-Shock", "Joggable" "G-Shock Protection" (Used by Sony), etc.
- Joe Wiesennfelder, Portable Audio, Spin, Vol 11 No. 7, Oct. 1995, page 100