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Y8 - SU1.4 - Sound

⏱️ Do It Now

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Lesson 4 - Summer 1 - Sound


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📝 Do It Now

Answer each of the following:

(1) Explain what a pixel is and how it works.

 

(2) A 3 byte binary number is used to represent the colour of each pixel. What does each byte of the binary number represent?

 

(3) What is this colour? #00FF00

 

Extension Question: Discuss the benefits and the limitations of reducing the colour-depth of an image.

 

🎯 Learning Objectives

  • LO1: Be able to outline the properties of sound waves
  • LO2: Be able to describe the process of sampling a sound file
  • LO3: Be able to explain the number of bits per sample and how many samples are recorded per second

📖 Everybody Reads

Sound Waves

Sound waves are essentially vibrations in the air, that travel outward from their source to our ears.


The vibrations affect the air pressure around them and it is this difference in air pressure that is picked up by our ear drums or by a microphone.


📖 Everybody Reads

Amplitude and Frequency


The frequency of a sound wave is how many waves occur per second. Low frequencies generate a low pitch and high frequencies generate a high pitch.


The amplitude of a sound wave is the size of the individual waves. A high amplitude sound wave is loud and a low amplitude sound wave is quiet.

📝 Activity

Amplitude and Frequency Generator


(1) Experiment with different frequencies and amplitudes.

(2) Using several screenshots of the wave generator to help you, outline what the frequency and amplitude of a sound wave are.

Interactive Sine Sound Wave

Pitch
Medium Pitch
Amplitude Effect
Medium Loudness
Wavelength
0.78 m
Wave Speed
343 m/s

📝 Written Activity

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📝 Amplitude and Frequency

Instruction:

  • Take several screenshots of the sound generator app you have just used
  • (1) Demonstrate what is meant by frequency; providing a screenshot of what a high and low frequency wave look like
  • (2) Demonstrate what is meant by amplitude; providing a screenshot of what a high and low amplitude wave look like

📖 Everybody Reads

Sampling Sounds

When sound is recorded by an electronic device (computer, phone, tablet) it is converted into 1s and 0s by a special device called an analogue to digital converter (ADC for short).


📖 Everybody Reads

How The ADC Works

The ADC takes regular samples (readings) of the amplitude and stores these as 16 bit binary numbers

The standard sample rate(how many samples are recorded per second) is 44.1 kilohertz. This means 44,100 samples are recorded per second!

🔎 Practical Demonstration

Example of Audacity

Your teacher will demonstrate samples by using Audacity


If you are working independently, please watch this video

🎥 Audacity Demonstration

📝 Written Activity

Copy this into your OneNote Page and complete it

📝 How sound is recorded

Instruction:

  • Identify the device that records analogue sound waves as binary numbers
  • Explain what a sample is, and how many bits are used for each sample.
  • Explain what is meant by hertz, and how many samples are recorded per second

Plenary Activity

📝 MWB Reflection Task

Open the mini-whiteboard app in a new tab

Your teacher will start with these leading questions:

  • Define Amplitude and Frequency
  • What is each sample a recording of?
  • How many samples are recorded per second?
  • How many bits are stored in each sample?