OK, now we know about bits and also how come copy them indigenous one place to another. But where exactly do we put all these bits in the first place?

One acquainted digital storage tool is the compact disc (CD). Bits space encoded on a CD together a series of pits in a metallic surface. The length of a pit coincides to the state the the bit (on or off). As we’ve seen, that takes a many bits to save high-quality digital audio—a standard 74-minute CD can have more than 6 exchange rate pits top top it!


Figure 2.21This photograph shows what standard CD pits look prefer under high magnification. A CD shop data digitally, making use of long and also short pits to encode a binary representation of the sound for analysis by the laser mechanism of a CD player. Thanks to evolution Audio and video in Agoura Hills California for this photo from their A/V news (Jan 1996). The magnification is 20k.

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Figure 2.22Physically, a CD is written of a thin film the aluminum embedded in between two discs the polycarbonate plastic. Information is videotaped on the CD as a collection of microscope pits in the aluminum movie arranged along a constant spiral track. If expanded linearly, the monitor would span over 3 miles.Using a low-power infrared laser (with a wavelength that 780 nm), the data space retrieved from the CD making use of photosensitive sensors the measure the strongness of the reflected light as the laser traverses the track. Because the recovered bit stream is just a bit pattern, any kind of digitally encoded information have the right to be stored on a CD.

Putting whatever Together

Now that us know around sampling rates, bit width, number systems, and also a lot of other stuff, how about a nice practical example that ties it every together?

Assume we’re composers functioning in a digital medium. We’ve acquired some cool sounds, and also we desire to keep them. We need to figure out how much storage us need.

Let’s assume we’re working with a stereo (two independent channels of sound) signal and 16-bit samples. We’ll use a sampling price of 44,100 times/second.

One 16-bit sample take away 2 bytes of storage space (remember the 8 bits equal 1 byte). Because we’re in stereo, we need to double that number (there’s one sample because that each channel) to 4 bytes per sample. Because that each second of sound, us will record 44,100 four-byte stereotype samples, providing us a data price of 176.4 kilobytes (176,400 bytes) per second.

Let’s review this, because we understand it can get a bit complicated. There space 60 seconds in a minute, for this reason 1 minute that high-quality stereo digital sound take away 176.4 * 60 KB or 10.584 megabytes (10,584 KB) of storage space. In bespeak to store 1 hour of stereotype sound at this sampling rate and resolution, we require 60 * 10.584 MB, or around 600 MB. This is an ext or much less the lot of sound details on a typical commercial audio CD (actually, it can store closer come 80 minute comfortably). One gigabyte is equal to 1,000 megabytes, for this reason a conventional CD is roughly two-thirds that a gigabyte.

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Figure 2.23

One good rule of ignorance is the CD-quality sound right now requires around 10 megabytes per minute.