How audio products work.

Authors Avatar

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 
  1. Blank and recordable 

A pre-recorded Minidisk is exactly like a CD, except smaller. A CD holds about five times more data (650 megabytes in data mode and 740 megabytes in audio mode) than a Minidisk. However, both CDs and Minidisks can store the same amount of music (75 minutes or so). The difference is that a Minidisk uses a digital compression technique called ATRAC (Adaptive Transform Acoustic Coding) when storing music.

A recordable Minidisk is a magneto-optical device capable of storing 140 megabytes of information. Music can be scattered all over the disk and the player can "put it together" correctly when playing the disk. This means that you can erase and re-record songs on a Minidisk without having to worry about how they fit together. This is tremendously convenient compared to a cassette tape, where you have to basically re-record the entire tape if you want to change any of the songs on it. There are also 4-track Minidisk recorders for musicians, which are great for recording songs as they are performed and then mixing the tracks.

Source: http://www.cdman.com/technical/howdocdswork1.html

How Do CDs Work?

Like gramophone records, the information on optical discs are recorded on a spiral track. However, with a CD the laser starts reading the disc from the inside ring (table of contents) and ends up on the outside. When play back starts, a laser beam shines on the ridges and lands on the data membrane layer. If you look at the image on the right you can see the data layer moving in grey.

Join now!

During playback, the number of revolutions of the disc decreases from 500 to 200 rpm (revolutions per minute) to maintain a constant scanning speed. The disc data is converted into electrical pulses (the bit stream) by reflections of the laser beam from a photoelectric cell.

Cutaway view of the laser pickup. Depending on whether the laser beam hits a ridge or a land, the laser beam is reflected and received by the photoelectric cell. The disc data is converted into electrical pulses (the bit stream) ...

This is a preview of the whole essay