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What is digital?

Module by: CJ Ganier. E-mail the author

Summary: Explains the difference between analog and digital.

To understand what it means for something to be digital, it is easiest first to explain its complement analog. The world around us is filled with analog signals: the temperature of the air around changes continuously, sound is the undulating change in pressure of the air at our ears, and the ocean moves up and down with the curve of waves. An analog signal has the advantage of being able to represent every value possible, however, the disadvantage of this is that any small error will alter the signal. Over time, many small errors can become a large error. When we measure the temperature outside as about 75 degrees, the analog measurement might be 75.433 degrees. We round off to 75 degrees because for many purposes, we don’t care about the extra .433 difference.

Figure 1: Sound as an read by the voltage from a microphone. The shape characterizes an analog signal.
An analog signal
An analog signal (image1.jpg)
Figure 2: Same signal as above but with noise added, a very different sound.
A noisy analog signal
A noisy analog signal (image2.jpg)

A digital signal rounds off all values to a certain precision or a certain number of digits. Thus a digital thermometer might be able to indicate that the temperature was 75.4 or 75.5 degrees but not 75.433 degrees. The advantage of a digital signal is that, because it automatically rounds off, it is much more resistant to errors. A digital signal can ignore the many small errors which, over time, would become a large error in an analog signal. Errors that appear in a signal are called noise. As long as the volume of the noise remains small relative to the difference between two levels of a digital signal, the noise will not affect the digital signal at all. Any amount of noise affects an analog signal.

Figure 3: A digital signal and its logical interpretation.
A digital signal
A digital signal (image3.jpg)
Figure 4: A noisy digital signal can still maintain the same logical interpretation.
A noisy digital signal
A noisy digital signal (image4.jpg)

In computers, the digital signal is either on or off. If a signal’s voltage level is close to 0V then it’s interpreted as off or 0. If the signal is close to the operating voltage of the device, say 3.3V, then the signal is interpreted as on or 1. Voltages in between are rounded off to on or off, but most devices are designed to keep the signals at on of the two extremes. While the computer operates as if the signal were either a 1 or a 0, the underlying voltage is still an analog value like .121V or 3.1.V

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Definition of a lens

Lenses

A lens is a custom view of the content in the repository. You can think of it as a fancy kind of list that will let you see content through the eyes of organizations and people you trust.

What is in a lens?

Lens makers point to materials (modules and collections), creating a guide that includes their own comments and descriptive tags about the content.

Who can create a lens?

Any individual member, a community, or a respected organization.

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| A lens I own (?)

Definition of a lens

Lenses

A lens is a custom view of the content in the repository. You can think of it as a fancy kind of list that will let you see content through the eyes of organizations and people you trust.

What is in a lens?

Lens makers point to materials (modules and collections), creating a guide that includes their own comments and descriptive tags about the content.

Who can create a lens?

Any individual member, a community, or a respected organization.

What are tags? tag icon

Tags are descriptors added by lens makers to help label content, attaching a vocabulary that is meaningful in the context of the lens.

| External bookmarks