vtec applied science unit 1 physics this video is about analog and digital signals basically what are the differences between them so first of all what is a signal a signal is basically information traveling from one place to another it could be a television signal which uses radio waves um an electrical signal in a wire if you talk into a microphone that produces an electrical signal which travels through the wire it could be an internet signal going to your computer through an ethernet cable that might be infrared or it might be visible through a fiber optic cable a mobile phone signal which uses microwaves wi-fi signal which uses kind of microwaves radio waves as well or a bluetooth signal see the mobile the wi-fi and the bluetooth use very very similar kinds of waves they overlap with each other but information traveling from one place to another is a signal an analog signal if you looked at an analog signal with an oscilloscope you'd see something like this it might contain lots of different frequencies its amplitude can vary quite a bit uh for example fm radio like normal boring old-fashioned radio um the electrical signal that goes to a loudspeaker is an analog signal and the sound that the speaker produces is an analog signal lots of different frequencies amplitude all over the place a digital signal however is made up of binary digits or bits and a binary digit is either a one or a zero so a digital signal is either one or zero it only has one amplitude it's either on or off it's up or down it's this or that it's a binary thing a one or a zero uh lots of examples of digital signals the internet is digital mobile phone signals our digital bluetooth wi-fi digital television digital radio they're all digital signals now digital to audio when we talk into a mobile phone well that's an analog signal which has to be changed into a digital one and there's a device called an adc an analog to digital converter which does that okay it converts an analog signal from the microphone into a digital signal and the process is called sampling what happens inside the adc is something called sampling many times a second what the the machine does is it looks at the value of the voltage many many times a second it looks at the value of the voltage and it changes it into a binary code so if you look at the graph here many many times a second the level of the voltage is converted into a binary code and you end up with a binary signal okay now there are two factors which will affect the quality one of them is the sampling rate and the sampling rate is how many samples are taken every second for example with high quality music they take about 44 000 samples every second i think with um telephone conversations it's about 8 000 samples every second okay the sampling rate and secondly the sampling sensitivity which is basically how many levels there are and how close the levels are together then the more accurate the sampling will be if you've got lots and lots of levels close together then you'll get accurate sampling to do that you'll need lots of bits per sample digital images how do you change a picture into digital well what you do is you split the picture up into lots of picture elements or pixels and then the color of each pixel has a binary code okay normally we can't see pixels because they're very very very small the idea is that they are so small that you can't see individual pixels if they were too big then the the image would look pixelated as this harry potter thing does now the screen of a television is made up of pixels it's made up of red green and blue picture elements it might be lcd which is liquid crystals or light emitting diodes but basically they're so small that we can't see them we just see the overall picture why are all signals nearly all signals digital now because there's lots of advantages of advantages of digital signals they can carry lots more information in the same bandwidth i'll talk about that a bit more in a minute the bandwidth is how much of the electromagnetic spectrum they use if they pick up interference and all signals might pick up interference it's easier to filter it out because it's easier to recognize it if you look at this digital signal here it's picked up a little bit of interference but it'll be very straightforward just to filter that out computer memory and processing is all digital computers are digital and they can deal with digital signals very very easily there are a couple of disadvantages if you process digital signals it takes a little bit of time which might involve a delay these days now that we have broadband we can handle lots and lots and lots of information at the same time that's not so much of a problem as it used to be the quality depends on the sample settings in other words the sampling rate and the number of pixels etc okay now everybody wants to send signals you know there's the public there's private companies there's the army scientists air traffic control ham radio radio normal radio digital radio everybody wants to send signals and it's very important that all these signals don't interfere with each other so everybody gets a little bit of a chunk of the possible frequencies that you might want to use the government allocates a bandwidth a bandwidth is part of the electromagnetic spectrum that they are allowed to use for example mobile phones are allowed a certain bandwidth okay air traffic control is in a certain bandwidth that nobody else is allowed to use the army has its own bandwidth amateur radio has its own bandwidth now with a digital signal in the same bandwidth you can get a lot more signals 20 years ago we had six analog television channels okay there was only six television channels and that was because that was all that could fit in that bandwidth now we have hundreds of digital tv channels all of them fantastic quality entertainment which uses the same amount of bandwidth