What is the sample rate of a sound recording?

the number of samples taken each second. It is measured in hertz: samples per second.

What is the sample resolution?

the number of bits used to store each sample. More bits per sample means each measurement is more precise.

What is the effect of increasing the sample rate?

a more accurate recording and a larger file. More samples follow the wave more closely, and there is more data to store.

A sound lasts 10 seconds. It is sampled 1000 times a second with 8 bits per sample. What is the file size?

10 000 bytes. 10 × 1000 × 8 = 80 000 bits, and 80 000 ÷ 8 = 10 000 bytes.

Why does sound have to be sampled before a computer can store it?

Sound is analogue, and a computer stores only binary values. A continuous wave has to be turned into separate numbers.

Sound · Cambridge IGCSE Computer Science (9

In plain words

Sound is a wave: a smooth, continuous change in air pressure. A computer cannot store something continuous, so it measures the height of the wave at regular moments and stores each measurement as a binary number. That is sampling.

Take more measurements each second, and measure each one more finely, and the stored sound gets closer to the real thing. The file also gets bigger.

5 things to know

A sound wave is analogue. It is sampled so that it can be converted to binary and processed by a computer.
The sample rate is the number of samples taken in one second, measured in hertz (Hz).
The sample resolution is the number of bits used to store each sample.
A higher sample rate or a higher resolution makes the recording more accurate (closer to the original sound) and makes the file larger.
File size in bits = sample rate × sample resolution × length of the recording in seconds.

Worked example

A sound is recorded for 30 seconds at a sample rate of 8000 samples per second and a resolution of 16 bits. Calculate the file size in bytes.

File size in bits = 8000 × 16 × 30 = 3 840 000 bits.
There are 8 bits in a byte: 3 840 000 ÷ 8 = 480 000 bytes.

Tips and tricks

Rate is "how often" and resolution is "how finely". They are two different things, and questions often ask for both.
When asked for the effect of a higher sample rate, give both effects: better accuracy and a larger file.

5 questions, about 2 minutes.

It lands in your notebook with its questions as flashcards.

Sound: 5 questions and answers

These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.

What is the sample rate of a sound recording?
- the number of bits in each sample
- the number of samples taken each second (the answer)
- the loudness of the sound
- the length of the recording
It is measured in hertz: samples per second.
What is the sample resolution?
- the number of samples taken each second
- the number of bits used to store each sample (the answer)
- the size of the file
- the number of speakers used
More bits per sample means each measurement is more precise.
What is the effect of increasing the sample rate?
- a less accurate recording and a smaller file
- a less accurate recording and a larger file
- a more accurate recording and a smaller file
- a more accurate recording and a larger file (the answer)
More samples follow the wave more closely, and there is more data to store.
A sound lasts 10 seconds. It is sampled 1000 times a second with 8 bits per sample. What is the file size?
- 1250 bytes
- 8000 bytes
- 10 000 bytes (the answer)
- 80 000 bytes
10 × 1000 × 8 = 80 000 bits, and 80 000 ÷ 8 = 10 000 bytes.
Why does sound have to be sampled before a computer can store it?
- Sound is too loud for a computer.
- Sound is analogue, and a computer stores only binary values. (the answer)
- Sound waves travel too slowly.
- Computers cannot use microphones.
A continuous wave has to be turned into separate numbers.

5 questions

Tap an answer and you’ll see straight away whether it’s right, and why.

Worksheet

2 questions, 5 marks. Write your answers on paper, then check them.

Sound

Cambridge IGCSE Computer Science (9–1) 0984 · 5 marks · papermunch.org

Name ______________________________ Date ______________

Describe how a sound wave is converted so that a computer can store it.[2]
Show answerHide answer
The height (amplitude) of the wave is measured at regular intervals. Each measurement is stored as a binary number.
I got this one
A recording lasts 20 seconds. The sample rate is 16 000 samples per second and the sample resolution is 16 bits. Calculate the file size in kibibytes.[3]
Show answerHide answer
625 KiB. 20 × 16 000 × 16 = 5 120 000 bits. ÷ 8 = 640 000 bytes. ÷ 1024 = 625.
I got this one

Answers: Sound

1. The height (amplitude) of the wave is measured at regular intervals. Each measurement is stored as a binary number.
2. 625 KiB. 20 × 16 000 × 16 = 5 120 000 bits. ÷ 8 = 640 000 bytes. ÷ 1024 = 625.