Video: Good vibrations

﻿Hi, I'm Darini. Welcome to lesson four of data representation going audio-visual. For this lesson, you will need to instal a free audio reading software, Audacity, so be sure to ask a parent or carer's permission before installing the software on your device. You will also need pen and paper to make notes. Remove as many distractions as you can, and when you're ready, let's get started! In this lesson, you will recall that sound is a wave. You will be able to explain the function of microphones and speakers as components that capture and generate sound. You will be able to define key terms, such as sample, sampling frequency or rate, sample size. You will be able to describe how sounds are represented as a sequence of bits. The form of sound. The nature of sound. Sound is a wave. Vibrations can set particles in motion, generating variations in density that is pressure points. So whenever a moving object or a vibrating objects, they can set the particles of air in motion, generating the variations in air pressure. On the right, you can see the particles in motion, which generates the low density, or the low pressure points, that you can see only few dots, and throw some high density, or high pressure points, that you see more dots within that specific point. Here's a Scratch programme to see an animated illustration of the nature of the sound wave and how it links to variations in air pressure. Here is a Scratch animation which illustrates the nature of sound in wave form, and how it links to the variations in air pressure. So when I switch on the microphone, see what happens. So, the microphone, which captures the sound in the form of air pressure points, and it converts them to electric voltages, the variations in electric voltages, which mirrors the air pressure points. That's what you see on screen in the wave form. Components for sound. Which component is used to capture sound? What do you think? Did you guess it right? Brilliant! Well done! The microphone, it captures the sound. So microphones allow devices to capture sound as electricity. So the input to microphone is the air pressure. We saw that in the Scratch animation. So microphones' input is the air pressure point, the variations in air pressure points. And what microphone starts is convert variations in pressure to variations in electric voltage, so its input is air pressure, but its output is electric signals, the electric voltages, and those variations in electric voltages mirrors the variations in air pressure. But the digital devices represent these waveforms as sequence of binary digits. So which component is used to generate sound? We know microphone is used to capture sound, so which component is used to generate the sound? What do you think? That you hear the sound. Speakers! Did you get it right? Well done! Speakers allow devices to generate sound from electricity. So speakers is the opposite of microphones, so it generates sound from the electric voltages. So speakers' input is the voltage, and the output is the air pressure. So speakers convert the electric voltages into air pressure points, the variations in air pressure, okay? Whereas the microphones, they convert the variations in air pressure to variations in electric voltage. But the digital devices product these wave forms as a sequence of binary digits. Task one: the form of sound. Use Audacity to examine how different sounds have different forms. You will need audio files, so make sure to download all the audio files you have been provided with to examine the different forms of sounds. Pause this video to complete your task, and resume once you're finished. Analogue to digital. Analogue and digital, these waveforms on the right are analogue, they are continuous streams. Individual points can have any value. Now the challenge: how can they be digitised? That is, how can they be represented as a sequence of binary digits? So how are we going to represent the waveform to sequence of binary digits? What do you think? We are going to do an unplugged activity, which explains a bit more about how to convert an analogue waveform to digital, that is, sequence of binary digits. Carrie is going hiking on a 10-hour trail on Mount Digi. Okay, so that's what you see on the bottom of the graph, zero zero to 10 hours, so she goes hiking on a 10-hour trail. And this is an example of her altitude, that is, how high she is, which may change along the route, okay? Taking samples at regular intervals. She promises her worrying parents that she will send hourly updates with her altitude, that is how high she is at the moment, so that they can trace how she is doing. Carrie's parents say that they don't need the details, so they don't want to know a lot about it, all they need is a two-bit code for how high she is. So they agree that a rough estimate will be efficient, so they don't need the exact details. So all they need is a two-bit code to represent how high she is. So she has to send these details every hour to her parents. Okay, so she will be sending a two-bit code for how high she is. How many possible altitude ranges for two bits do you think? Did you guess this right? Yes, it's four, two power two, two squared, that's four. So when you're sending two-bit code, or when Carrie is sending two-bit code to her parents, she will have only the four possible altitude ranges. That will be zero zero, zero one, one zero, and one one. So for this scenario, we can keep zero zero as low altitude range, zero one as a medium range, and one zero as a high altitude range, and one one as a very high altitude range. Analogue to digital. So the first message, what do you think she will send the first message as? Is she in zero zero, zero one, one zero, or one one altitude range? What do you think? So her first message to her parent is zero one. Because she is in the altitude range zero one. And again, these are approximate values. Okay, what do you think the second message, her second message to her parents, will be? One zero! Yes, you guessed it right, one zero! Okay, so her first message is zero one, her first message is zero one, and her second message is one zero. Okay, so what do you think will be her third message to her parents? It is the same, one zero. Do you think you can work out the rest of the messages, based on her route? So you could identify what messages she will send from zero two to 10 hours. Do you think you can do that? Then using the worksheet, work out the messages that Carrie will send to her parents every hour. Make sure you pause this video to complete your task, and once you have completed, resume this video. Welcome back! Task two: analogue to digital solutions. Let's see whether you managed to get all the answers correct for this one. Because you got the route, all you need to identify is what message she will send to her parents. That is, the two-bit code. Okay, so first message is zero one. Second message is one zero. Third message is one zero. Fourth message is one zero, and fifth message is one zero. Okay, she's in the same range for them, and she's sending this four different messages in the same range, same altitude range. And then she reaches the high altitude range, which is one one. And she goes back to one zero, one zero again, and then goes low from the eighth hour, which is zero one, ninth hour, it's zero one as well, and in the tenth hour, she has reached zero zero. So did you get all the answers correct? Well done! So what you have done here is you have turned the continuous, that is, analogue wave, the continuous stream, you have digitised it into a sequence of binary digits. Back to analogue. 'Kay, we're reconstructing back to analogue. So these are the messages that Carrie's parents have received. Zero one, one zero, one zero, one zero, one zero, one one, one zero, one zero, zero one, zero one, zero zero. How can they retrace Carrie's route? All we need is an approximate route. Okay, because within every altitude range, you can have a low, medium, or high within each individual altitude range. So where you draw your points, it's your choice. Okay, but as long as it is within the altitude range and you have drawn it correctly, that's fine. Okay, so how can they retrace Carrie's route? Reconstructing back to analogue. The first message they received is zero one, okay? And we don't know the exact altitude, so we going to mark just the middle of zero one range, so when you mark the altitude range, either choose the middle, top, or bottom. That's your choice, okay? But it should be within that altitude range, that's all. Okay, the second message they received was one zero. Do you think you can reconstruct the rest of the route? Yeah, we are looking for an approximate route, as long as it is within the altitude range, that's perfectly fine, okay? So now it's your turn to complete the task three, which is back to analogue. So using the worksheet, retrace Carrie's approximate route for hiking. Yes, not the exact route, because we don't have the exact altitude information, so approximate route for hiking based on the messages received by her parents. So make sure you look at the altitude range for that hour, and mark the point within that altitude range. So pause this video to complete your task. Once you have completed, resume this video. So far, we have seen analogue to digital using two bits, so you can have four combinations of altitude ranges. What about if you have three bits, if you're using three bits? How many possible altitude ranges can you have? Eight, that's correct! So here, there are eight possible combinations, using the three bits, okay? So here's an example of Carrie sending messages to her parents using three bits, and for every half an hour. Since she is using three bits, there are eight different altitude ranges, and you can see this graph is more accurate, okay? So at least we have more information, but it's at the bottom or the middle or the top, okay? Since we got eight possible altitude ranges. Digitising sound. Digitising sound: the challenge for you was to represent the analogue, that is, continuous stream of sound wave, as a sequence of binary digits. And that's what exactly you done with the Carrie's messages to her parents using the altitude ranges. You take the sample voltage at regular time intervals, so that's the first step. When you're digitising sound, you take the sample voltage at regular time intervals. Similar to the Carrie's case, she sent messages every hour, or every half an hour. So you take the sample electric voltage at regular time intervals. The number of samples taken per second is called the sampling rate. So what does the sampling rate? It's the number of samples taken per second, and its typical value, for example, is 44,100 samples per second. The second step, it's to record a sequence of bits for each sample, like this. So the number of bits recorded per sample is a called a sample size, so the number of binary digits assigned per sample is called the sample size. On the right-hand side, you can see it has the sample size of 16 bits, okay? Sample rate is the number of samples taken per second, and the sample size is the number of binary digits assigned per sample. Okay, here is an example. Look on the right-hand side. Each dot stands for a sample. In this case, a sample size that's the number of bits assigned per sample is 16 bits, so our sample size is 16 bits, and the sampling rate, that is, the number of samples taken per second, is 44,100 samples. So it takes 44,100 of these 16-bit samples to represent a single second of sound. With 90 samples in the image, we are looking at point zero two seconds of sound. Only a part of the sound, okay? Because it's 90 samples out of the 44,100 samples taken in a second. The big picture. Any moving object can set particles of air in motion, generating variations in pressure, or density. And microphones capture the sound, so microphone converts the variations in air pressure to variations in electric voltages, and this is what you see in the wave form on screen. Okay, and analogue representation of wave form is the continuous streams. Speakers generate sound, and speakers convert electric variations and electric voltages to variations in air pressure. And finally, we use zeros and ones, that's a sequence of binary numbers, to digitise analogue representation. And sample rate is the number of samples taken per second, sample size is the number of binary digits recorded per sample. I would love to see your work! If you would like to share your work with Oak National, please ask your parent or carer to share your work on Instagram, Facebook, or Twitter, tagging @OakNational and #LearnwithOak. Hope you enjoyed this lesson! See you in lesson five!

Worksheet: Good vibrations

Exit Quiz: Good vibrations

Completed: Good vibrations

We would advise you to complete this lesson on a desktop device as you need to download and interact with additional files as part of the learning. These can be downloaded from the last slide of the worksheet. You should always ask your parent or carer for permission before downloading files from the internet.

Tracing the steps of a hiker through the altitude data that she transmits, learners will familiarise themselves with the basic concepts necessary for understanding any analogue to digital conversion; samples, sampling rate, and sample size. 

Computing

Good vibrations

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