Editors Note: This note briefly discusses analog and digital transmission technologies, and how they work.
Human beings use analog techniques for listening and viewing content. Our eyes and ears create electrical waveforms that our brain can process. A shift in waveform translates into changes in the intensity of the signal, which our brain perceives as a change in frequency and volume. The larynx and the ear drum contain diaphragms that (respectively) create and duplicate the waveforms. We communicate by modulating changes in frequencies onto the vibrations (waveform) created as air moves across the larynx. We hear waveforms when sound vibrates (modulates) a signal onto our ear drums.
Even in an environment where digital devices and networks operate, human listening and viewing will continue to occur in an analog mode. The device used for speaking and listening and for viewing content must convert digital signals back to the analog format humans use. One way to understand this concept would be to examine how speakers and microphones work. The speakers we use to reproduce music and telephone calls take an electronic signal and convert it into physical vibrations which correspond to sound.
The microphone function in telephones and other electronic devices operates in the reverse. Instead of translating electronic signals into sound, microphones take auditory vibrations created by sound sources such as the larynx and convert the vibrations into extremely low powered electronic signals. Vibrations passing through a membrane, combined with a receptive electronic field, convert sound into an electronic signal that can be amplified and subsequently converted into a digital signal.
Converting analog signals into a digital format has several advantages. Digital signals do not degrade when duplicated, nor do they accumulate noise and other interfering signals when amplified. Additionally devices such as computer hard drives can quickly store and retrieve digital files thereby facilitating quick, cheap and high quality duplication of content. Analog duplicates generate significant noise that appears as hiss, cracks and signal distortions on an audio cassette and snow, blurring and color deviations on a video cassette. Digitally made duplicates more accurately replicate the desired signal and can more readily ignore and filter out noise, offering superior signal regeneration.
Digital signals also lend themselves to easier processing to achieve a number of desired results. Because digital signals do not readily spill over into adjacent frequencies many different signals can ride together, piggy-back style, on a broadband carrier. Substantial operating efficiencies accrue when a network can collect lots of traffic headed in the same direction and inject all the individual communications links onto a single pipe.
Digital signals also make it possible to reduce the size (bandwidth) of the pipe needed to send multiple or high complexity signals, such as a high definition television channel. Because digital signal processing uses signal sampling techniques, the number and type of sampling can be adjusted. The process known as compression uses techniques to predict the characteristics of the next sound or frame of video content. Using predictive techniques and reducing the frequency of waveform sampling can result in the processing of a less than optimal, but adequate audio and video signal while using much less signal transmission capacity.
Other digital signal processing advantages include ease in coding and decoding signals to preserve privacy, referred to as encryption and deencryption. As well, digital technologies lend themselves to the constant reduction in price per processing function seen in the regular decline in price for digital processing devices such as compact disk and DVD players, digital televisions and computers.
On the negative side digital technologies contribute to consumers’ desires for broadband networks that operate with faster bit rates and offer greater throughout. People with high speed Internet access at work grow accustomed to quick file downloading and expect ventures to offer similar access opportunities at home. Digital devices and services use more complex technologies and typically cost more. Lastly digital technologies need to interface with human requirements (for example the need to convert digital signals to analog) and with existing networks. Because of the cost in making the conversion to digital technologies, ventures typically make the migration incrementally. This means that telecommunications operators first will retrofit existing analog networks to provide some digital services, before they replace analog technologies. Typically these operators will not replace the last few kilometres of wire that link individual offices and houses until they have completed network upgrades further up the switching hierarchy.