# Lesson video

In progress...

Hi, I'm Dharini.

Welcome to lesson five of Data Representation, Going Audio Visual.

For this lesson, you will need a free audio editing software, Audacity.

So be sure to ask your parents or carers' 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 crack on.

In this lesson, you will calculate representation size for a given digital sound given its attributes.

You will be able to explain how attributes such as sampling frequency and sample size affect characteristics such as representation size, and perceived audio quality.

You will be also able to perform basic sound editing tasks using Audacity, and combine them in order to solve more complex problems requiring sound manipulation.

Representation size.

How many bits are required to represent a piece of sound? How can you calculate the number of bits needed to represent a piece of sound? In order to calculate the number of bits needed to represent an audio file, the first information you need is a sampling rate.

Sampling rate is the number of samples recorded per second.

And the next bit of information you need is a sample size.

It's the number of binary digits assigned to every sample.

So when you multiply the sampling rate by the sample size, you will get the total number of bits in a second.

And when you multiply that by the duration of the audio file, then you will get the total number of bits needed to represent that audio file, for that given duration.

And finally, you will also need another bit of information.

It's the number of channels.

When you listen to music using your headphone, each speaker outputs a different sound.

That uses two distinct channels.

For movies, they may use many different channels so they can output different sounds to different speakers.

And in similar way for home theatres as well, they may use multiple channels in order to output to different speakers.

Using the worksheet, compute the size of audio files.

Make sure to pause this video to complete your task, and once you have completed resume this video.

Welcome back.

Representation size.

So assume that you have a digital recording of a sound, the duration is one second, the sampling rate is 8,000, and the sample size is one byte.

So use this information to compute the number of bytes required to represent this sound.

Okay.

So in order to calculate the representation size, you multiply the sampling rate by sample size and its duration.

So we multiply 8,000 samples per second by one byte and one second.

So the total number of bytes required to represent this sound is 8,000 bytes.

Did you get this right? Well done.

Okay.

Now convert this 8,000 bytes to kilobytes.

So if you have to convert 8,000 bytes to kilobytes, you divide by 1000.

So 8,000 divided by 1000, answer is eight kilobytes.

Now for the part two, you open the sound file clarinet.

wav.

The duration is 10 seconds.

It's sampling rate is 44,100 samples per second.

The sample size is 16 bits per samples and it has two channels.

So use this information to compute the number of bits required to represent this sound.

So in order to calculate the representation size in bits, equal to multiply sampling rate by sample size, duration and channels.

Sampling rate is 44,100 samples per second, multiplied by 16 bits per sample, multiplied by 10 seconds, that's is the duration.

And that is multiplied by the two channels.

We get 14,112,000 bits.

Convert this size to bytes or kilobytes.

So in order to convert 14,112,000 bits to bytes, we have to divide that number of bits by eight.

So when you divide 14,112,000 divided by eight, you get 1,764,000 bytes.

And then you want to find the kilobytes, you have to divide 1,764,000 by 1000.

So you will get 1,764 kilobytes.

Right click on the sound file of clarinet.

wav and view its properties.

What is the actual size of the file? It's 1,764,000 bytes, is the size that you computed in the previous step identical, or even similar to the actual size of the file? What do you think? Yes, we got the same answer.

So it is identical.

So what are the advantages of sounds with high sampling rate and a high sample size? Sounds with a high sampling rate and high sample size are great because of the increased quality.

But why increased quality? So high sampling rate means we are recording more samples per second, and high sample size means we are assigning more binary digits per sample, which increases the ability to accurately match the original analogue signal.

But remember the Carrie's hike in lesson four, why send so many messages with more bits? Why do you need to send so many messages with more bits? Because you need to get the accurate information? Why not? But it's not so great because of the increased representation.

So when Carrie sent two bits as a message to her parents, she used four possible combinations.

The storage size was less, but when she actually adapted it to three bits for every message, the storage size slightly got increased.

So it's not so great because of the increased representation.

More space is required for storage, and more effort required for processing, and more time required for transmission.

So the advantages of sound with high sampling rate and a high sample size, are increased quality and increased ability to accurately match with the analogue signal.

But it's not so great because of the increased representation.

That means more space is required for storage, more effort and time required for processing and transmission.

Audacity demonstration.

So you will be using Audacity to edit your sound files.

So as part of editing sound file, we are going to open the sound file, count.

wav, which counts number one to 10.

So in order to open the file, you will use the menu, File, Open, or you can use the shortcut Control + O, if you want to play the sound file, you will click on the play button in Audacity or you can press the space key.

This is what the Audacity environment looks like.

At the top, you've got the menu.

And underneath the menu, you've got six buttons.

So the first button is for pausing the playback.

The second button is for playing the audio file, and the third button is for stopping the playback.

So before you edit any audio file, make sure to click stop the playback because you cannot edit an audio file while it's running.

The next two buttons are for start of the audio file and the end of the audio file.

And the last button is for creating your own recording.

The other two tools we might use today, are the Selection tool, and the Zoom tool.

Okay.

So as part of our task one, let's open the count.

wav.

So go to the file menu, click Open.

And make sure to choose the right file from the folders.

I'm opening count.

wav.

So this is the count.

wav file, on the left, you can see the information about the count.

wav.

The sample rate is 44,100 Hertz, and the sample size is 32 bit.

Okay.

So in order to play the file, all you got to do is either click on the play button, or press space.

One, two, three, four, five, six, seven, eight, nine, 10.

Next you will select a particular word to play back.

So distinct words in the audio are visible when you examine the form of the wave.

So in order to examine the form of the wave, you have to zoom in, okay, so you can use the Zoom tool or you can press f4 to zoom in.

Okay.

So you can click on the Zoom tool, left click will allow you to zoom in, and if you want to zoom out, it's Zoom tool and right click together, to zoom out.

You can alternatively, you can also use the keyboard shortcut, Control + 1 to zoom in to particular sound wave, and Control + 3 to zoom out.

So we are going to select a particular word from the audio to play back.

Second part of the task is selecting a particular section of word within the audio file.

So in order to do that, I'm going to zoom in.

Okay.

So to zoom in, I use the Zoom tool, and left click.

So Zoom tool and left click allows me to zoom into the audio wave.

I can clearly see how big that is, okay.

But if you want to zoom out, it's a Zoom tool.

So it's a Zoom tool again, and then right click to zoom out.

Okay.

Now I'm going to select the word one.

So I'm going to select the word one.

Okay.

So in order to do that, I click on the select tool, click and drag where I needed it.

Okay, so I have selected one.

Just hear it and see whether you have selected the right one.

One.

Second part of this task is we are going to delete a section of an audio.

So choose one of the words, so you called words from one to 10, so choose one of the words to delete.

Okay.

So all you have to do is you've got to first select the word, make sure you zoom in, either by pressing Control + 1, or click on the Zoom tool and the left click.

Okay.

So once you have selected, you can click on edit, delete, or just press Delete.

Okay.

But if you want to undo any of your action at any point of time, you can click on Edit, Undo or use the keyboard shortcut Control + Z.

After deleting a part of the audio, make sure to play the audio, to see whether you have achieved your goal.

And if you think you have, then make sure to export as WAV using the option File, Export, Export as WAV.

Third part of the task is to delete a section of an audio.

Okay.

So in order to delete a section of an audio, you got to select a particular section of an audio you want to delete, and then click on Edit and Delete, or press the Delete button in your keyboard.

Okay, so I have selected one, the word one, and I'm going to delete it by either going to Edit, Delete or the Delete key in your keyboard.

So I'm going to click on Edit, and Delete.

Okay.

So now I want to play back the audio to see whether I have achieved the right results.

So I should not hear the word one.

Okay.

So I'll go to the beginning of the audio.

So in order to go to the beginning of the audio, click on that icon, okay.

Let me play back and see.

Two, three, four, five, six, seven, eight, nine, 10.

So we got, we haven't got the number one.

Okay.

In order to export my file, I'm going to click on file menu and click on Export, Export as WAV.

I'm going to give a new name to the file.

So I have typed in count_edited.

So once I'm happy with the file name, I'm going to click on Save.

So what are the default values that has been given? I'm going to accept it by clicking on OK.

Okay, so now my new file has been saved.

So part three of this task is moving a section of an audio.

We're going to use Cut and Paste to move a section of an audio.

So select one of the words within the audio, use the Selection tool.

And if you want to select a particular word, make sure to click Zoom tool and left click to zoom in, zoom tool and then right click to zoom out, or Control + 1 to zoom in, and Control + 3 to zoom out.

And once you have selected one of the words, go to Menu, Edit, Cut, or use the keyboard shortcut Control + X.

So click in the position of the audio where you want to paste it, use the menu, Edit, Paste, or you can use the keyboard shortcut Control + V.

You can press Control + Z, or Edit and Undo in the menu options to undo any of your actions.

The next part of the task is to move a section of an audio.

So this time I'm going to select the word two.

Okay.

So, make sure you have zoomed in using the Zoom tool and the left click or Control + 1.

I have already zoomed in so I'm going to just make a selection by using the Selection tool.

So click on the Selection tool, highlight the word you want to move.

Okay, so I'm going to, I have highlighted the word I want to move.

Okay.

And then it's Edit and Cut.

So I have cut the section I want to copy, and then I'm going to paste it at the end.

Okay.

I'm going to paste it in the end.

So I go to Edit.

and Paste, or Control + V.

Okay.

So now I'm going to play the whole audio files.

All I have to do is go to the click on the start of the audio file and now I play it, I should be hearing the two at the end.

One, three, four, five, six, seven, eight, nine, 10, two.

So at any point of time, if you think you have made a mistake in Audacity, all you've got to do is go to Edit and Undo.

Or you can press the keyboard shortcut Control + Z.

Part four of this task is applying effects.

So select a part of the audio.

So in order to select a particular section of the audio, make sure to zoom in by pressing Control + 1, or Zoom tool plus left-click.

And to zoom out is Control + 3 or zoom plus right-click.

So once you have selected a particular section within the audio, then you can apply any one of the effects.

Okay.

So in order to apply the effect, choose the menus, Effect and choose one of the options to the selected section of the audio.

If you're happy with the effect that has been applied, make sure to play back to see whether you have achieved your results.

If so, export the audio to a proper sound file as File, Export Export as WAV and give a different name.

Okay.

My ten and two are closer together.

So what I want to do is I want to fade in.

So how do I do that? Select the part of the 10, the last part of the 10.

Okay.

I can see up to here, last part of the 10 and go to Effect on the menu and then it is Fade In.

Okay, so click on Fade In.

Okay.

So now I go back to the start of the video, and play the audio.

One.

Three, four, five, six, seven, eight, nine, 10, two.

Okay, so there's a gap in between 10 and two.

Okay.

So you can apply any effect you want for any section of the audio.

Okay.

So make sure to select what you want to apply the effect for, for example it's 10, then it's Effect, and then choose the effect you like, okay.

And see what happens with the output of the audio.

So once you're happy with the actions, all you've got to do is you've got to click on File, Export, Export as WAV.

I'll check to make sure I have chosen the right folder, and I'll give a different name.

So I'm going to give a sensible name to reflect the actions I have done with the audio file.

So I have done, what I have done here is move a section of an audio using Edit, Cut, and Edit, Paste.

And I also applied an effect, fading in.

So my new file name is count_move_effects.

When you come up with this dialogue box, just accept the default values given by the system and click OK.

Well done.

You worked really hard today.

I would love to see your edited audio files.