Lesson video

Hello, my name is Mr. Hogan.

I'm so excited to be learning with you today.

We're gonna have such a great time learning about data representation of images and sounds.

I'll be supporting you with our learning during these lessons.

I'm so pleased that you've decided to complete your learning with me today.

We are going to do brilliantly.

Welcome to today's lesson from the unit, Data Representation: Images and Sounds.

This lesson is called Representing Sounds with Binary Data.

By the end of the lesson, you'll be able to describe how a sound is represented in digital devices.

I'm really looking forward to this lesson.

I hope you are.

We have four keywords in this lesson.

Sample.

This is a single measurement of a analogue signal, typically a sound.

Sample rate.

The number of samples captured per second.

Sample resolution, or sometimes known as bit depth, is the number of bits used to store each sample, which determines how accurately the sample is represented.

And our final keyword is channel.

This is a single stream of audio used to reproduce sound.

Remember, you can come back to these keywords at any time during this lesson.

Just rewind it.

So this lesson is split into two.

The first part is, describe how sound is represented in digital audio.

And the second part is to calculate the size of a sound file.

So let's start.

Describe how sound is represented in digital audio.

I'm so looking forward to it.

I hope you are.

What words come to mind when you think of sound? Laura is saying, "Waves." Sam is saying, "Vibrations." Alex is saying, "Volume or loud." And Sofia is saying, "Pitch or bass or treble." You may have heard of some of these words about sound or maybe you haven't.

Perhaps you've heard of different ones.

But hopefully we're going to look to see how sound is represented in digital audio.

So sound is a wave.

Vibrations can set particles in motion, generating variations in density or air pressure.

So you can see the air pressure in the form of a wave in the diagram.

And then we have particles.

And the low-density particles are low pressure.

So that's represented with that first rectangle where the wave is low.

But then where the wave is higher, it has high density and high pressure.

So the particles are closer together.

That's represented on the right-hand side of that diagram.

So let's have a look at it in motion.

This is an animated illustration of a sound wave.

So when two people are talking and having a conversation, this is the sound wave and the particles moving.

Let's have a quick check.

What causes sound to travel? Is it A, light reflecting off objects, B, vibrations creating waves of pressure in the air, or C, electricity flowing through wires? Remember, you can pause the video at any time or even rewind it.

Let's have a look at the answer.

It's B, vibrations create waves of pressure in the air.

Laura is saying, "Sound waves are created "when sound is created in the real world." But Alex is asking, "How can I create sound "to use on a computer?" Well, let's see if we can answer Alex's question.

Microphones allow devices to capture sound as electricity.

Microphones convert variations in pressure to variations in electric voltage.

And digital devices represent these waveforms as sequences of bits.

So the digital representation are in binary numbers.

Let's have a look at it the other way around.

So digital devices produce these waveforms from sequences of bits.

Then how do we start to listen to those bits? Well, speakers allow devices to generate sound from electricity, and then speakers convert variations in electric voltage to variations in air pressure.

So that's how we start to listen to digital sound.

This image shows how a sound wave is sampled.

Each dot represents a sample along the top of this sound wave.

And each sample have different bits.

In this example, it's 16, so the sample is 16 bits.

The sample rate could be 44,100 samples per second.

It takes 44,100 of the 16-bit samples to represent a single second of sound.

The number of samples taken per second is called the sample rate.

Typical value is 44,100 samples per second.

For each sample, a sequence of bits is recorded.

The number of bits recorded per sample is called the sample resolution or sometimes known as bit depth.

A typical value is 16-bits per sample.

Let's have a check.

What does sample rate refer to in digital audio? Is it A, the number of speakers used to play a sound, B, the volume of the sound being recorded, or C, the number of sound samples taken per second? Remember, you can pause the video at any time or you can rewind it to look for the answer.

Shall we have a look at the answer? It is C, the number of sound samples taken per second.

I'm hoping you're enjoying the lesson.

I know I am.

Let's move on.

We're gonna have a practise now.

So Alex is saying, "I want to record a podcast "about my hobbies." So, one, how do vibrations create sound waves that we can hear? Two, explain what hardware Alex will need to record his voice and listen to the recording.

Three, how is digital sound stored? And, four, describe how digital sound is created, stored, and converted from analogue to digital.

Remember, you can pause the video at any time or even rewind it and look at parts that we've done before.

Some suggested answers here.

So, one, how do vibrations create sound waves that we can hear? When something vibrates, it pushes the air around it.

This makes the air particles squeeze together and spread apart, causing different air pressures.

Two, explain what hardware Alex will need to record his voice and listen to the recording.

To record his voice, Alex needs a microphone to capture the sound and turn it into a digital file.

To listen to the recording, he needs headphones or speakers.

How is digital sound stored? Sound is stored as sequences of bits, zeros and ones.

Hopefully you've got these right.

But don't worry if you haven't.

We'll move on to the next one.

Describe how digital sound is created, stored, and converted from analogue to digital.

So quite a long answer to this question.

Digital sound is created by converting analogue sound waves into electrical signals using a microphone.

The sample rate is the number of samples taken per second, so, for example, 44,100 samples per second, which determines how frequently the sound wave is measured.

The sample resolution, or sometimes known as bit depth, refers to the number of bits used to record each sample, so, for example, 16 bits per sample, which affects the detail and accuracy of the sound's amplitude.

These sample values are stored as sequences of bits representing the digital version of the sound.

When played back, speakers convert the digital data back into electrical signals, which are then turned into sound waves.

That's a big answer.

Hopefully you've got some of that, if not most of that correct.

Well done.

We're gonna move on to the second part of the lesson now.

I've really enjoyed the first part, and hopefully you've learned how to describe how sound is represented in digital audio.

Now we're gonna look at calculating the size of a sound file.

Alex is asking, "I am ready to record my podcast.

"I'm going to make it really high quality." Laura's asking, "That's great.

"Do you know if you have enough storage space "on your computer?" Alex replies, "I've not thought about that.

"How do I work that out?" Laura's commenting, "I suppose you need to work out "how much storage space your podcast will use." Yes, Laura's right.

You do need to work out how much storage space your podcast will use in order to find out if you've got enough storage on your device.

Better quality sound files need more storage space.

To calculate the total storage needed for a sound file, you need to know the following: the sample rate, the sample resolution, and the duration of the sound.

Let's have a quick check before we move on.

Which of these affects the size of a digital sound file? Is it A, the volume setting on the speakers, B, the sample rate, or C, the amount of storage on the computer it is saved on? Pause the video at any time or rewind it if you want to look and try and find the answer out.

Shall we have a look at the answer? It is B, the sample rate.

How many bits are required to represent a piece of sound? So let's take a look.

So we've got our sample rate, we've got our sample resolution.

So we multiply them together.

That gives us how many bits used in a second.

So then we need duration, so the amount of seconds of sound.

We multiply that with the bits in a second, and that gives our representation size.

So total bits for a piece of sound.

The duration of the sound is one second, the sampling rate is 8,000 samples per second, and the sample resolution is one bit per sample.

So let's put those numbers in here.

So the sample rate, sample resolution, multiply them together, gives us bits in a second.

And then multiply that by the duration, and that will give us the representation size.

So let's put 8,000 as the samples in the second, and then we've got one bit in a sample.

And then we multiply it by the seconds of sound.

So, in this example, it's one.

So this gives us 8,000 bits.

So 8,000 bits is the size of the representation, the total bits for a piece of sound.

Laura is saying, "When I listen to music or watch films, "sometimes I hear different sounds from each headphone." Alex also is commenting, "Yes, sometimes it's used in movies, "like when there's a car chase.

"The sound of the car starts in one headphone, "then stops and starts in the other headphone." Channels in sound are used to separate these streams of audio.

Each channel adds to the overall sound you hear.

Left and right speakers or headphones play slightly different sounds to create an immersive experience.

In mono audio, there's only one channel that delivers the same sound to all speakers or headphones.

In stereo audio, there are two channels, one for the left and one for the right.

In surround sound systems, multiple channels are used to produce sound from various speakers positioned around the listener, really enhancing the immersive experience.

I know I've experienced this when I've gone to the cinema before and watched a movie where you are almost like in the movie and you can hear sounds from behind you, in front of you, and to the side of you.

Let's have a quick check.

What is the main difference between mono and stereo audio? Is it A, stereo audio is louder than mono audio, B, mono audio has one channel while stereo audio has two channels, or C, mono audio is used for music while stereo audio is used for speech? Remember, you can pause the video at any time or rewind it to previous slides to help you.

Shall we have a look at the answer? It is B, mono audio has one channel, while stereo audio has two channels.

Hopefully you got that right.

But don't worry if you didn't.

We're having a really good time on this lesson, and we'll move on.

Alex is asking, "I was thinking about adding more channels "to my sound file.

"Do you think that would make it sound better?" Laura's replying, "Yes, I think so.

"But wouldn't that make the file size much bigger?" Good question, Laura.

Let's take a look.

By adding channels, the sound file becomes larger.

So let's have a look to see how this works.

So we've got this sample rate multiplied by sample resolution, gives us bits in a second.

We've done that before.

And then we've got the duration.

Yeah, we've multiplied that before.

And that gives us the representation size.

But now we have to multiply that by the number of channels.

So if the duration is 10 seconds, the sampling rate is 44,100 samples per second, the sample resolution is 16 bits per sample, and it has two channels.

Let's take a look at this.

So 44,100 samples in a second, 16 bits in a sample, we're putting in 10 seconds of sound now.

We're gonna multiply it by 2, having two channels.

So that gives us 14,112,000 bits.

That's a lot of bits in that piece of sound.

Laura's commenting, "We've calculated "the size of the sound in bits, "but what does that really mean? "How can it be changed so it is easier to understand?" So we can convert this size to bytes or kilobytes.

One byte is eight bits.

So for that 14,112,000 bits, we can divide it by 8 to give us 1,764,000 bytes, which equals 1,764 kilobytes.

So that's a lot easier to understand, isn't it? Let's have a practise.

One, what four things do you need to know to calculate the storage size of a sound file? Two, how is stereo sound different from mono sound? Remember you can have a think about this, pause the video, or you can rewind it at any time.

Three, why might a surround sound system need more digital storage space than a stereo system for the same piece of music? Remember, pause the video anytime or you can rewind it.

Four, Alex has created a musical introduction to their podcast.

The sound recording is 30 seconds long, it has a sample rate of 22,050 samples per second, and a sample resolution of eight bits per sample.

And it uses two channels because it's stereo.

A, calculate the total number of bits needed to store this sound recording.

B, how many bytes is the musical introduction? Remember, you can pause the video anytime or rewind it.

So time to look at some answers.

So, one, what four things do you need to know to calculate the storage size of a sound file? So to calculate the storage size of a sound file, you need to know the sample rate, the sample resolution, duration of the sound, and don't forget the number of channels.

Two, how is stereo sound different from mono sound? A stereo sound has two channels, that left and right channel, while mono sound only has one channel.

Three, why might a surround sound system need more storage than a stereo system for the same piece of music? Well, surround sound systems use more channels than stereo, which means they store more data and result in larger file sizes.

Four, Alex has created a musical introduction to their podcast.

The sound recording is 30 seconds long, it has a sample rate of 22,050 samples per second, and has a sample resolution of eight bits.

It uses two channels, stereo.

A, calculate the total number of bits needed to store this sound recording.

So we've got 22,050 samples per second multiplied by 8 bits, multiplied by 30 seconds, multiplied by 2 'cause it's two channels.

So this gives us 10,584,000 bits.

B, how many bytes is the musical introduction? So this is where we divide by 8 bits.

So it is 10,584,000 bits divided by 8 bits.

This gives us 1,323,000 bytes.

Well done, you've reached the end of the lesson.

You've done so well.

I've really enjoyed learning with you today.

So, today, hopefully you have learned that sounds are represented digitally using samples.

Sample rate is how many samples are taken per second.

A higher sample rate generally means better sound quality.

Sample resolution, sometimes known as bit depth, is the number of bits used to represent each sample.

Higher bit depth also improves sound quality.

And channels refer to the number of audio tracks in a sound file.

Well done, I've really enjoyed today.

Thank you very much.