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How audio products work.

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Introduction

Katie Sheppard GNVQ Media Audio unit 5 How audio products work. There are several standard music distribution formats. The MP3 and the compact disc (CD) are the two most common at the moment, but cassette tapes are still around. The Sony Minidisk is another format that Sony has been trying to popularize for many years. A Minidisk looks a lot like a floppy disk but is slightly smaller (7 cm, 2.75 inches square). CDs store 74 minutes of music in a nearly indestructible form and have the advantage of being a digital format, but until fairly recently you could not record on a CD. The Minidisk's main claim to fame is that it is (and always has been) recordable. One easy way to think about a Minidisk is like a floppy disk -- you can record and erase files on a Minidisk just as easily as you can on a floppy disk. The big difference between the a Minidisk and a floppy disk is that a Minidisk can hold about 100 times more data. Minidisks come in two forms: 1 Pre-recorded 2 Blank and recordable A pre-recorded Minidisk is exactly like a CD, except smaller. ...read more.

Middle

The difference in height between the two places is exactly a quarter of a wavelength of the laser beam light, so the original beam is totally eliminated by the interference between the beam reflected from the surface of the disc and the beam reflected from the ridge. The photocell does not produce current. It should be noted that the ends of the ridges seen by the laser are "ones" and all lands and ridges are "zeros"; thus turning on and off the reflection is one, steady state is a string of zeroes. As it is not possible to have two ones next to each other, Eight to Fourteen Modulation (EFM) is used to convert 8-bit data bytes to 14 bit units that always have a minimum of 2 and a maximum of 10 zeros between ones. This makes the pits/ridges and lands separating them 3 to 11 bits long, no less, no more. This conversion is done in hardware using a ROM lookup table. To connect these 14 bit units 3 merge bits are used to make sure that there are no "ones" too close to each other. ...read more.

Conclusion

CDs should be cleaned radially: not along the grooves, but at right angles to the direction of the grooves. If a smear, however small, should remain on the CD, running along the direction of the grooves, much information would be lost. It is advisable to use special CD cleaner that operates with a rotating brush at right angles to the direction of the grooves. Many people think that the digital CD is produced completely digitally, but this is not always the case. Many CDs have an analogue master tape as their source tapes still kept in the library of the record company, used in the past to make records. The quality of a CD made from analogue tape can be surprisingly high. A CD recorded, processed and dubbed digitally does not always sound better than a CD produced with one or two analogue processing stages. To indicate what stages have been treated in what ways, a useful three-letter code is used on recordings. The letters represent: the recording, the editing/mixing process, and dubbing, respectively. They are printed on the CD and/or on the insert label in a rectangular box. There are three possibilities: DDD (completely digital CD); ADD (analogue recording, digital processing and dubbing); and AAD (analogue recording and processing, digital dubbing). Many CDs carry the ADD or AAD indication. ...read more.

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