Data rates

Data are patterns of bits that have meaning when correctly decoded. Data can be described in terms of number, size, format, type, and other descriptive variables. The speed that data can be encoded (stored), transferred, decoded (retrieved), and processed is called the data transfer rate. Data rates are important when sending and receiving data. If the transfer rate is too fast, or too slow, accurate data transmission may not occur and information can be lost.

 Data Image

Music Box

Analog

Analog data are variable across a range of values. Brightness of visual stimuli and loudness of sound are examples of analog data. Analog data tend to deteriorate when copied. The random nature of the data makes correcting deterioration difficult.

Analog data uses a parameter with great variability to encode the data. An analog recording carries relative information about the frequency and volume of the information that can be directly reconstructed to represent the original data. For example, audio frequency or volume can both be represented by a sine wave. Frequency is represented by the length of the wave with the height of the wave to indicate the volume.

Examples of Analog

Examples of analog media include:

• Photographs that use varying sizes of silver compounds held in a backing media to capture the range of light to dark tones and colors in a given scene.
• Records that use variation in a series of grooves to store pitch tone and volume of audio signals.
• Microphones that use a variety of techniques such as a diaphragm moving in a coil or piezoelectric crystals that convert changes in audio pressure into electrical signals.
• Wire/tape recordings that use a magnetic head to record and playback information. Depending on the electronics associated with the recorder, either analog or digital audio and video signals can be recorded to tape.

Digital

Digital data is composed of bits of information with binary values of 0 or 1. Examples of digital media include:

• Punch cards and tape, which were used for early computer data storage.
• Bar codes, which use digital stripes of light and dark to encode product information.
• CD-ROM and DVD that optically store digital information such as audio video, and computer data.

Advantages of Digital

A significant advantage of digital data over analog is its ability to be copied repeatedly with no deterioration. Analog data can be converted and encoded to digital form for storage and transmission, then decoded to recreate the analog signal.

Transfer of Data

Sometimes, transfers of information are not perfect, and errors occur. The analog information stored on audio CDs is relatively unaffected unless relatively large error rates occur when reading and writing data. Due to the redundancy of data used to carry information, digital audio and video have a much greater tolerance for errors than computer data. Often errors in audio and video data go unnoticed, or can simple be corrected by using averaging to insert "cover" data to replace errors of omission during data transmission. For example, audio CDs can loose up to about 10% of the data without affecting listening.

Error Handling

Digital information is much less forgiving of errors during reading and writing data. Unlike analog information, digital information is carried by random bits of data with no inherent pattern. Since it is not possible to predict missing bits, correction of errors has to rely on verifying the accuracy of the copy or transmission. Typically verification involves checking accuracy, then if necessary re-reading or re-sending the data, then checking once again until a correct copy has been transmitted.

The random patterns of digital information, such as computer data, can require significant efforts to detect errors and request re-reading or re-transmission to acquire correct replacement data for critical applications when errors do occur.

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