VirtualPBX.Com tech tutorials explain certain technical details of general interest to anyone using our VirtualPBX, cell phones, computers, or other electronic equipment.

Readers are also referred to the Analog-Versus-Digital page in the website CellPhoneInfo.com which includes the complete context for cell-phone technology.

Since analog and digital systems appear everywhere these days; it is useful to have a short discussion on what the terms mean and what these systems are. This is something which almost everyone has to come to terms with sooner or later, and the pervasiveness of digital systems in our society is only going to increase with time. It is the power of digital computers which allows them to take over many complex information tasks and which makes sophisticated services like the VirtualPBX possible.

Basically analog or digital refers to the method used to convert information into an electrical signal. Telephones, microphones, measuring instruments, vinyl record players, CD players, tape decks, computers, fax machines, etc. must all convert information into an electrical signal in some manner so that it can be transmitted or processed. For example, a microphone must convert the pressure waves which we call sound into a corresponding electrical voltage or current which can be sent down a telephone line, amplified in a sound system, broadcast on the radio, and/or recorded on some medium.

In an analog system, an electrical voltage or current is generated which is proportional to the quantity being observed. In a digital system the quantity being observed is expressed as a number. This is really all there is to it, but there are a few details which must still be discussed.

For example in a electronic analog thermometer, if the temperature being measured is 83 degrees, then the analog system would put out, for example, 83 volts. This could just as well be 8.3 volts or any other voltage proportional to the temperature. Thus if the temperature doubled to 166 degrees, the output voltage would double to 166 volts (or perhaps 16.6 volts if the instrument were so scaled). The output voltage is "analogous" to the temperature.

In the case of an electronic digital thermometer, the output would be the number 83 if the temperature were 83 degrees. Hence it is based on "digits". The only thing that is wrong with this example is that 83 is a decimal number constructed from the ten symbols 0, 1, 2, ..., 8, 9. We commonly use ten symbols in our numbers for historical reasons; probably because we have ten fingers. Ten symbols, however, is inconvenient if it is desired to express it as an electrical voltage. It is much more convenient to have only two symbols, 0 and 1. In this case, 0 could be represented by zero volts, and 1 by 5 volts, for example. This is known as a binary (only 2 symbols) number system, but the principle is still the same: the output of the digital thermometer is a number, i.e "digits".

When only two symbols, 0 and 1, are used; it is possible to count exactly as we do with our ordinary numbers only we run out of symbols sooner. For example in a normal number system when we count past 9, there are no more symbols left; and we construct the next numbers with combinations of the previous symbols, 10, 11, 12, 13 , etc. In the case of only 0 and 1, we must combine the old symbols to make more numbers much more often. Thus 0, 1, 2, 3, 4, 5, 6, 7 etc. would be written 0, 1, 10, 11, 100, 101, 110, 111, etc. Almost all digital systems use this method of expressing numbers with 0 being zero volts and 1 being 5 volts. For the thermometer example above, 83 is the binary number 1010011; and the electronic thermometer would send the sequence, 5 volts, 0 volts, 5 volts, 0 volts, 0 volts, 5 volts, and 5 volts to express the number 83 in binary.

A digital system may seem more complicated than an analog system, but it has a number of advantages. The principal advantage is that once the measurement expressed in digital form, it can be entered into a computer or a microprocessor and manipulated to gain a number of improvements.

An equally important advantage of a digital representation is noise immunity. Everyone has heard static on an AM radio during a thunder storm or had their FM car radio become noisy when they stopped at a red light in a dead spot or behind a hill. In the digital case the equipment looks at the voltage being sent and decides if it is a zero or a one. The dividing line is half way in between, 2.5 volts. For example, if a zero were sent, the noise or static must be strong enough to reach a level of 2.6 volts before it would be mistaken for a one. Thus in the digital case the noise must be 50 percent of the signal level or more to he heard at all. In an analog signal our sensitive ears can easily hear one to 10 percent noise. Thus digital systems are generally less noisy than analog ones.

Other examples of analog systems are the normal telephone system or a microphone or a loud speaker. In the case of speech or music, the signal is made up of tones. For example with a flute, the tone is an almost pure sine wave wiggling up and down at the frequency (tone) of the instrument. In this case, an analog signal in an amplifier or a telephone would have a voltage which went up and down just like the sound, i.e. the voltage is "analogous" to the tone.

As mentioned above, digital systems are more complicated than analog ones. For this reason, the early electronic systems were analog; and we still have them with us today. The first analog system ever used was Alexander Graham Bell's or Elisha Gray's telephone. Bell and, independently, Gray constructed microphones which converted the pressure from sound waves into electrical voltages "analogous" to the form of the sound wave. These were send down a pair of wires to an ear piece which vibrated proportionally (analogous) to the electric voltage and reproduced the sound.

AM and FM broadcast radio are also analog systems. A microphone converts sound wave pressure into an electrical voltage which is impressed on the radio wave. When a receiver picks up the signal, the original voltages from the microphone cause the radio's loud speaker to vibrate reproducing the original sound.

Digital systems did not become practical until silicon microprocessors and integrated circuit technology made it possible to deal with very complex systems. Today digital systems are everywhere: CDs, digital cell phones, VirtualPBXs, digital sound in the movies, watches, palm pilots, electronic ignition, smog control, vehicle diagnostics, antilock brakes, Hi-Definition TV, cash-register scanners, computers, etc.

In addition to noise immunity, the hallmark of digital systems is their ability to do very very complicated operations. Because of this cell phones are possible today. Only a few years ago they were impossible. (See the tutorial What Is a Cell Phone?)

(Anyone who wishes to check that 83 is really 1010011 in binary may do so in one of two ways. The most laborous way would be to simply count to 83 in binary as illustrated above with 0, 1, 10, 11, 100, etc. This gives the best learning experience but takes a while. If you have Windows, a simpler way is to bring up the Calculator by using the Start button at the bottom left of the screen to choose Programs, then Accessories, then the Calculator. Under View select Scientific. Next enter 83 in the window and click on the button marked Bin. 1010011 will appear in the window.)