Image and Sound Representation Component 1.4 Image and Sound Representation

Assessment Outcomes Grade 4 - 5 Explain the digital storage and sampling of sound Grade 6 Explain the effect of sampling intervals on the size and quality of sound files Grade 7 Evaluate the different stages of converting sound into a digital form

Starter: Entry Ticket Use your pre-reading notes to help you answer the entry ticket. Extension Define the following keywords in your book: Sample Frequency Analog Sound wave (use a diagram) Digital Sound wave (use a diagram) Sound Resolution

Sound Representation As we have already established, a computer system is only able to store and process binary digits, as it is a digital device. Since this is the case, how can sound be stored as it is an analogue signal not digital? If an analogue signal, such as sound, is sent to a computer system, it has to be converted into a digital signal before it can be processed.

Analogue Sound waves are analogue, which means that they continuously change. Computers cannot store analogue signals. They must be converted in order for the computer to use it.

Digital Anything stored on a computer must be stored as a series of binary numbers or digital. Digital signals are exact and square.

Analogue-to-Digital Converter (ADC) The device that converts the analogue wave to digital is know as the analogue-to-digital converter or ADC. You might know this as a sound card.

Storing sound waves Storing analogue sound waves as numbers is very easy. We match the interval with the resolution

Resolution This is the number of bits used to store each sample. The more accuracy you have the larger amount of numbers you will need.

Sample Frequency The number of samples taken in a given time period. The more samples taken the better the quality of feedback

Sampling Sound is converted into a digital signal by a process called sampling. Sampling is where hardware, such as a microphone, measures the level of sound many times per second and records this as binary digits. The number of times that the sound level is sampled per second is called the sampling frequency. The higher the sampling frequency, the better the quality of the sound recorded. A typical sampling frequency is 44,000 times per second, also known as 44 kHz. This is the sampling frequency used on most audio CDs.

Sampling Sound sampled at 44 kHz in stereo will produce a large amount of data and as such, this data may need to be compressed. When sound files are compressed, data is removed to reduce the size. This reduction in size means that

Graded Exercises Complete the Grade 4 exam questions. You must write the question and the answer into your books. Extension Move on to the grade 6-7 exam questions.

Past Exam Questions Complete the Grade 6 and Grade 7 Exam questions. These should be self-assessed and stuck into your books. Grade 8 Extension You should research the following questions and give reference to where you found the information in your answer. Because this is grade 8 you are expected to put your answers into a lot of detail – this may require you to draw and annotate diagrams for images and sound. Images Explain where and when lower resolution images may be better Explain two other methods of reducing the file size of an image Find out what lossy and lossless compression are and explain using examples when each should be used Sound Name two things which can affect the quality of sound stored in a computer. Draw a diagram to show this. Think of a disadvantage of a large sample rate.

Plenary: Exit Ticket – Exam Question breakdown Complete the exit ticket, stick it in your book. Extension Continue with the graded exam questions and extensions.

Homework Question Sheets: Q25 – Images and Pixels Q26 – Image Size Q27 – Digitising Sound Exam Questions: Complete your Year 11 target grade Pre-Reading: 50-56 Notes on Data Types and Data Structures