Analogue Signals and Digital Signals – What are they?
Analogue signals are continuous in both time and amplitude. Analogue signals are used in many systems, although these days the use of analogue signals is declining due to the cheap production of digital signals. Countless natural signals, for example, heat and light, are analogue in nature.
A radio is a perfect example of a system which uses an analogue signal.
Digital signals are discrete in time and value. Digital signals are signals that are represented by logic values, “1” or “0”. There are only 2 levels in a digital signal.
Optical Fibres would be a modern communications system which would use Digital Signals.
The Evolution of Digital Age
Up until the middle of the 20th century, nearly all technology was analogue; the technology thus needed physical forces in order to operate, as digital needs some abstract quantity, such as numbers.
Early electronic technology was built using an important analog device called a vacuum tube. Such tubes were used to control the electrical current and voltage in in the likes of radios and very early computers. Unfortunately, similar to light bulbs, these vacuum tubes got very hot, and burned out regularly, thus needing to be replaced regularly. These would later go on to be replaced by transistors, a smaller, more reliable, cheaper alternative used to carry out all the functions of the vacuum tube, it is used in nearly all analog and digital systems today.
Analogue communication involves transferring an analogue waveform containing information with no digitisation between two users.
Examples of such media are:
Digital communications is the physical transfer of data (a digital bit stream) over a point-to-point or point-to-multipoint transmission medium.
Examples of such media are:
‘ copper wires
‘ optical fibres
‘ wireless communication media
‘ Storage media.
Advantages/ Disadvantages of Digital vs. Analogue Technologies
‘ Digital technologies can be mass-produced thus are less expensive
‘ They are more reliable (less moving parts e.g. record/cd players) and use less power thus the advent of devices like IPods etc.
‘ Digital data is much easier to store and manipulate.
‘ Digital data is much less prone to electrical ‘noise’ and thus can be transmitted much further. Also unlike an analogue signal a digital signal can be completely regenerated back into pristine condition.
‘ Can be copied multiple times without degradation. (E.G. copying an audio tape versus copying an CD)
‘ Greater bandwidth required for transmission (i.e. better quality cables needed).
‘ Errors in converting an analog signal like music to digital (not 100% accurate)
Example 1 ‘ Recording Music ‘ Analogue vs. Digital
In an analogue recording system (Vinyl), a physical recording medium is made to vary in a manner similar to the variations in air pressure of the original sound. First of all, the changes of air pressure are first converted (by a microphone) into an electrical analogue signal in which either the instant voltage or current is directly proportional to the instant air pressure. The variations of the electrical signal (caused by air pressure) in turn are converted to variations in depth of the grooves on the vinyl record by a recording machine such as a record cutter’the variable property of the record is modulated by the signal, and when the vinyl is replayed, it will reply the exact sounds as were present when the air pressure was changing, this thus makes it plausible to replay music on the vinyl records.
A digital recording (CD) is produced by converting the original sound into a series of numbers, which can then be stored and replayed for reproduction. Usually, the sound is transformed (with a microphone) to an analogue signal in the same way as for analogue recording, and then the analogue signal is digitized (converted to a digital signal) by an analogue-to-digital converter and then recorded onto a digital storage medium (CD).
Analogue Audio or Digital Audio?
It is still highly debated today whether analogue audio is better than digital audio or vice versa. The question is greatly dependent on the quality of the systems (analogue or digital), and other factors which are not necessarily related to sound quality. Arguments for analogue systems include the absence of fundamental error mechanisms which are present in digital audio systems, including aliasing (undistinguishable sounds), quantization noise, and the absolute limitation of dynamic range. Supporters of digital audio point to the high levels of performance possible with digital audio, including low levels of noise and distortion.
Very high quality sound recording is possible with both analogue and digital systems. Excellent, expensive analogue systems may outperform digital systems, and vice versa. In theory any system of either type may be surpassed by a better, more sophisticated and expensive system of the other type, but in general it tends to be less expensive and easier to achieve a decent standard of technical signal quality with a digital system, except when the standard of the system is very low. One of the most restraining aspects of analogue technology is the high sensitivity of analogue media to minor physical degradation; however, when the degradation is more distinct, analogue systems usually perform better, more often than not still producing recognizable sound, while digital systems will usually fail completely, unable to reproduce anything from the medium.
The main advantages that digital systems have are a very consistent source reliability, cheaper media duplication, and direct use of the digital ‘signal’ in today’s widespread portable storage and playback devices. Analogue recordings in contrast, require relatively big, high-quality playback equipment to capture the signal from the media as accurately as digital.
Example 2 ‘ Television ‘ Analogue vs. Digital
Analogue television is the first television technology that used analogue signals to transmit video and audio. In an analogue television transmission, features such as brightness, colours and sound are represented by very rapid variations of the amplitude and frequency of the signal.
Analogue signals vary over an infinite number of possible values which means that electronic noise and interference becomes reproduced by the receiver. So with analogue, a reasonably weak signal becomes hazy and vulnerable to interference. Similarly, a moderately weak digital signal and a very strong digital signal transmit equal picture quality. Analogue television may be wireless or can be distributed over a cable network using cable converters.
All broadcast television systems before the invention of digital television used analogue signals.
Digital television (DTV) is the transmission of audio and video by digitally processed and multiplexed signal, in contrast to the totally analogue and channel separated signals used by analogue television. Digital TV can support more than one program in the same channel bandwidth. Several regions of the world are in different stages of adaptation and are implementing different broadcasting standards.
Advantages / Disadvantages of Digital TV:
‘ Narrow bandwidth signal transmission.
‘ Requires less broadcast transmission power to operate.
‘ More compatible with modern day technologies as computers, DVD players, Blu-Ray, and up-to-date video processors in TVs etc.
‘ More precise, sharper, less blurry for higher resolutions
‘ Fragile signal (more susceptible to RF/EM interference)
‘ Reception is basically an all-or-nothing deal: if your reception isn’t of good quality, it’ll sound hazy, start pixelating, and can the picture can freeze, unlike analogue, where there may be some static but you can still see the picture and hear at minimum one channel of audio)
‘ Difficult to modulate, digital tuners more expensive than analogue
‘ Not backwards-compatible with older technology (i.e. analogue video).
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