Tag: compact disc players

Although I have heard that CD players are on average better at reproducing sound…

Lou Bloomfield Leave a comment

Although I have heard that CD players are on average better at reproducing sound, I have also heard that the best sound quality can still be had from high end phonographs. To what extent is this true?

The digitization process does introduce some distortions into the sound signal, including aliasing (confusion about high frequencies) and quantization error (round-off errors in recording the softest sounds). However, these distortions should be so small or at such high frequencies that they should be inaudible. Still, there are always some audiophiles who can hear (or claim to hear) these imperfections.

Do you know anything about a special kind of digital tape that could replace the…

Lou Bloomfield Leave a comment

Do you know anything about a special kind of digital tape that could replace the CD?

Digital audiotapes have been around for a few years. These tapes store sound as digital information on a tape. Because of the digital recording and playback, the reproduction is almost perfect. The digital process involves an enormous amount of information each second; too much to be recorded in the conventional method used in cassette tapes. Instead, I think that a helical technique is used, in which information is written as diagonal stripes across the length of the passing tape. By writing a closely spaced series of these stripes, the DAT (digital audio tape) player uses much more of the tape’s surface than a standard cassette and stores much more information on that surface. I doubt that DAT tapes will replace CD’s because CD’s are so easy to mass-produce. DAT tapes must be recorded one at a time.

How are the binary numbers represented in the ridges of the CD?

Lou Bloomfield Leave a comment

How are the binary numbers represented in the ridges of the CD?

In principle, the binary numbers could be written as the presence or absence of ridges (i.e. a 1000 nanometer long ridge could be a 1 while a 1000 nanometer long flat area could be a 0). However, this technique has technical problems. The main problem is that the number “0” would be a long flat region (16 adjacent flat regions would be one 16000 nanometer flat region). If the flat region became too long, the CD wouldn’t be able to follow the track any more. So an encoding scheme is used to make sure that ridges and flat areas are never too long. They use a length-encoding scheme, where ridges of different lengths correspond to a short group of binary bits. Furthermore, a very extensive error correcting arrangement makes sure that the music can be read even if a great many bits are unreadable. About 25% of the CD’s surface is dedicated to this error correcting information.

How does a laser diode work?

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How does a laser diode work?

A laser diode resembles a light emitting diode, in which electrons flowing across a p-n junction (in a diode) find themselves in conduction levels of the p semiconductor, with lots of excess energy. These excited electrons give up their excess energy by emitting light and they drop down into empty valence levels with much less energy. In a laser diode, the region in which this energy release occurs is a very narrow channel with mirrored ends. Instead of emitting their light spontaneously, the electrons experience stimulated emission. Light bounces back and forth between the ends of the channel and is amplified as it passes new excited electrons. Because all of the light produced by a laser diode emerges from one end of this very narrow channel, it experiences severe diffraction and spreads out into a wide, cone-shaped beam. To convert this cone of light into a narrow beam, a converging lens is usually attached to the diode laser’s housing and this lens bends the beam into a fine pencil of light. Most laser diodes operate in the red or infrared portion of the spectrum, although some laser diodes that emit blue light have recently been developed.