Or at least “explain it like I am an 8th grader.” I am a middle school science teacher and am struggling with explaining these concepts in a simplified way that my students can understand. They have some prior knowledge about waves and how they travel. I appreciate any help you can provide!
In: 8
Its how they‘re interpreted
In both cases the fundamental signal is just analog waveforms, thats how we physically transmit signals over eg. cables.
An Analog Signal is interpreted as is. You transmit a waveform and the amplitude, frequency and signal strength define what you transmit. If you transmit a sine wave with an anplitude of 2V and a frequency of 50hz thats all it will ever be. A good example would be a tin-can telephone. You speak into it, your voice vibrates the string and transmit this to the other side and on the other side a person can hear the voice. Now analog signals are very prone to external influences, eg. if you make your string ridiculously long it could be so far apart that the person on the other side might not hear anything or very quiet. Or if another string crosses yours you could pick up conversations from another Person. All those problems make analog signals not very „good“ however if you manage to transmit your signal without any influences or signal losses you will get a 1 to 1 transmission.
Digital signals are „encoded“. We basically defined that eg. 0-0.8V is considered „low“ or „0“ and 2-5V is considered „high“ or „1“. Now if we send a signal from one side to the other it doesn‘t really matter if a „high“ signal we send out with 5V reaches the other side as 4.3V due to signal loss and resistence. It will still be interpreted as „high“. Heck it can even reach it as 2.8V. As long as the signal stays in the before mentioned parameters we will always be able to correctly decode it and thus never lose informations due to exteriour influences. A good analogy would be thetin-can telephone from earlier, but instead of speaking into it and sending your voice to the other side, you want to transmit a message. And to transmit the message you use morse code by tapping the tin-can. Now as long as the person on the other side can clearly identify the taps it doesn‘t matter if they‘re quieter than the original ones because of the string length. Or if the taps sound a bit different in frequency. As long as you can make them out you will never lose informations. However while you did transmit 100% of the information, by encoding an analog signal into a digital one (like encoding the sentence (voice) you used to say over the tin-can telephone into morse code so you can tapp it and thus can never recreate the original voice that said the sentence on the other side even tho you transmitted the same information eg the sentence) you will unfortunately lose informations.
Thats what the difference in transmitting analog and digital signal means. Just how you interpret things.
The explanations are good, but perhaps it needs a bit of elaboration. Let’s say I want to send a signal, say music. At any point in time, the waveform is at a certain value, let’s say 100. With an analog signal you just send a voltage that represents 100.
With digital you only have on and off, 0 or 1.
So to send a value of 100, you need to send the value in what is called binary representation – a series on 0s and 1s – in this case 1100100. That’s seven bits of information.
So in some senses analog is easier, you just send a value that can drive a speaker or whatever. With digital, you need to convert it into binary, send those ones and zeros and then convert it back. The advantage with digital is the because you are only dealing with ones and zeros, there is less chance of it being affected by noise and signal degradation, because on the receiving end you know it’s going to be one or zero.
Analog signals are proportional to whatever you’re trying to control or whatever information you’re sending.
Example: Suppose you have a thermostat that controls radiator valves for heating. When the room is cold, the thermostat will send a small analog signal in the form of a direct current voltage between 0 and 10 volts (0-10 V DC) to the radiator valves. The valve opens proportionally to the analog signal….a 5 VDC will open the valve 50%, 6 VDC opens 60% and so on. The output signal from the analog thermostat is proportional to how much heat is needed in the room, and how much hot water is allowed through the radiator.
Digital signals (sometimes also called binary signals) are either 0 or 1’s. There is no in-between. These are used either when we just need and “on / off” control or we want to convert the information into computer code.
So for the thermostat example: a digital signal could be limited to either 0 VDC or 10VDC….no in between. In that case the radiator valve would only ever be fully open or fully closed….you’d still get heat to the room, but it would be an all or nothing approach. You would get full flow to the radiator, and once the thermostat was satisfied, the valve would close completely.
It would be like trying to control the speed of your car by only ever having your foot off the gas or putting the pedal hard to the floor.
To put it in an acoustic context, analog is like a police or fire siren (weeooo, weeooo). The frequency of the sound is continuously rising and falling, and that has a meaning to us.
Digital would be more akin to a telegraph using morse code (dot, dot, dot, dash). It’s on or off. Durations may change, but it’s always all or nothing.
Sound is inherently analog in nature, as is all things that could be described as a “wave”. So, even if you may have digital equipment between the recording and playback of that sound, it always starts and ends analog. Digital must “sample” that wave and approximate it by slicing it up many times per second.
Analog is the signal meat uses. Digital is the signal that computers use.
An analogy in two lines:
Analog signals are like pictures, you need to see the colors and shapes to see the whole thing.
Digital signals are like books, as long as you can read the text, the color or the strokes of the text do not matter.
That’s why replicating an analog signal accurately is difficult, any inaccuracies in transmission and replication distorts the signal. For digital signals, as long as you can make out the text, distortions do not matter.
Digital signal is discrete in time and discrete in value.
Between the time of the two datum of digital data, we do not know what the true value is. This information is lost when the digital data is created, or doesn’t exist at all. E.g. if you take a record of temperature of the room every day, you will not know from the record what the temperature is in the middle of the day.
The value of the datum is also discrete, i.e. on the record it’s always one of a per-determined set of values. A real value is recorded by approximately choosing from that set of values, whichever closest. Information is also lost here.
If we use music as an example. Digital audio only has 44100 datum per second. What it sounds like in between the datum is not known and can only be guessed with some assumptions. Each datum can only vary among 65536 values, even if most of the time it won’t be an accurate representation of the real values.
Analog is a wheelchair ramp and digital is a staircase. An analog signal can smoothly vary around a given value, while a digital signal can only exist in discreete values. Digit means finger, so think of how you count on your fingers: one integer at a time.
In terms of data processing and transmission, digital data often has only two states- off and on, yes and no, true and false, 1 and 0, etc. This protects the signal from interference because the reciever knows it only has two possible inputs, at the cost of having to handle a longer signal.
I’m on my phone. But if you google how an old phone line modem modulates and demodulates digital to analog and back you’ll get some neat charts. And that will help visualize the difference.
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