Analog vs. Digital

An analog signal is continuously varying with values over time. Original communications networks, television broadcasts, movies, photographs, and such provide full continual analog information, whereas digital signals use discrete values. Discrete means individual, not connected. These discrete values are a spaced sampling of a signal and then reassembled as a facsimile of the original. Another way to consider the difference is to consider enlargement of a photograph. An old photograph can be greatly enlarged with considerable quality and without the pixilation problems of enlargement of most of today’s digital images.

So if analog provides greater fidelity and clarity, then why have the communications network providers moved to digital networks?

Explore

Digital is either on or off. There is no in-between. Digital is a binary signal of logic values 1 or 0 per bit of information. These values are also referred to as high or low. The circuitry is Direct Current (DC) logic electronics with voltage levels of most often 5 Volts DC or 0 Volts DC. That is how the logic chips in the microelectronics will send the sequences of 1s and 0s to the processors for information processing.

But the natural world is analog. As you recall sound, images, video, temperature, wind speed, etc., contain continuous information over time. Analog means continual readings or occurrences over time. The conversion to digital invokes a sampling mechanism where many data point values are extracted to provide a good representation of the information in the original signal.

Digital signals, such as data from computers, is digitized from the source and does not go through any conversion process. The information is already arranged in bits (values of 1 or 0) and so the management of the data stream is simplified.

Another significant aspect of digital communications is compression. This is most common on cellular networks and other lower bandwidth systems. That means that the signals are again reduced in size (lower data values) and compacted with other signals to enable the lower bandwidth transmission for what would have needed higher bandwidth. The quality is somewhat reduced with compression because some of the data is lost in the process. However, in most cases, such as voice, the message can still be understood. The benefit is providing more message capability within a given bandwidth.

The topic of digital communications is very intense and much more information is available than can be presented in this course. The intent in this lesson is to provide high level basic information. Digital Signal Processing is a fascinating topic in Electrical Engineering and interested students are encouraged to research further information on their own.

Review the following information to understand the values of digital communications and the basics of Digital Signal Processing

What are other reasons for the huge investment for digital networks?

1. Computers communicate digitally – Much of today’s data is digital. Communications operating companies experience significant cost savings (capital and maintenance) for keeping the digital signal over conversion to analog and back again to digital.

2. Evolving User Services and Features – The in-demand features and services are software defined and thus digital.

3. Ease of Compression for bandwidth – Being able to pack more information channels within the transportation infrastructure provides significantly lower cost transmission of many more signals in the same bandwidth as would have been possible with analog signals.

4. Improvement of Noise over Analog – Digital does not reproduce the types of noise that is an inherent characteristic of analog signals. The noise can overwhelm the analog signal and make it unrecognizable. So digital improves quality.

5. Reliability (data networks) – Even though they carry digital services, not all digital networks are data communications networks. The difference is that data communications networks break the information into packets instead of continuous streams. Since information is fragmented into packets of information, those data packets can be routed individually and redundantly through data networks to be correctly reassembled at the destination.

Digital Signal Processing

Audio based information is analog in format. That means the electrical signal comes across as a waveform of variable voltage over time. The process of signal conversion from analog to digital requires points to be selected on the waveform of the electrical signal. Each of those points are converted into small strings of binary values (1s, 0s) called bytes and are further processed via complex mathematical algorithms into an outgoing digital signal. This signal is later reconverted to analog for recognition by the receiver. During initial signal conversion, the digital signal processing will filter out noise accumulated in the original analog signal.

Reference the following image for a representation of the analog to digital conversion process. Note the sequencing of bits into bytes for each data point. Typical output would be a string of characters such as 0010 and 0101.

Challenge

Take Away

The worldwide digital communication network has enabled the internet which is the information superhighway of our generation. Those of us in highly developed societies will often access and use the internet daily.

Take a look at this PBS Learning Media video titled A Cyber Privacy Parable and be prepared to comment in an upcoming assignment.

EngTech_LessonBottomBanner copy.png IMAGES CREATED BY GAVS