Sound Wave Lab
How a computer stores sound: turning an analogue wave into numbers by sampling, the sample rate and resolution that set the quality, the file-size sum of rate times resolution times seconds, and the quality against size trade-off.
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Turning sound into numbers
A real sound is an analogue wave that varies smoothly, but a computer can only store numbers. To bridge the gap it takes samples, measuring the height of the wave many times a second. This module works through sampling, the sample rate and resolution that set the quality, how to calculate a sound file size, and why better sound needs a bigger file.
Sound words to know
Learn these before you record a note.
Higher against lower
Turning the settings up captures the sound better but costs storage.
Digitise it, then size it
In the exam, treat sound like images: it uses the same kind of size sum. Sound starts as an analogue wave, and sampling records its height many times a second and stores each as a number. The rate says how often you measure, and the resolution says how many bits each measurement gets. To find the file size, multiply the rate by the resolution by the number of seconds. Turning either up gives better quality but a bigger file.
Match the term
- analogue
- sampling
- sample rate
- sample resolution
- a smoothly varying sound wave
- measuring the wave at regular moments
- how many samples per second
- the bits used for each sample
Match the fact
- a higher sample rate
- a lower sample rate
- more bits per sample
- the file-size sum
- captures the sound more accurately
- makes a smaller, rougher file
- stores a wider range of volumes
- rate times resolution times seconds
How is sound digitised?
How is an analogue sound turned into a digital file?
- By sampling the wave at regular intervals
- By printing it out on paper
- By playing it louder
- By deleting the quiet parts
True about digital sound
Select the TWO true statements about representing sound.
- The sample rate is the number of samples taken each second
- A higher sample rate gives better quality but a bigger file
- Sound is stored without ever being sampled
- Lowering the resolution makes the file bigger
Work out the sound file size
A sound is sampled 100 times each second, using 8 bits for each sample, for 10 seconds. Multiply the rate, the resolution and the seconds together, that is 100 times 8 times 10, to find the file size in bits. What is the answer?
Order the sampling process
Put the steps of digitising a sound in order, earliest first.
- Start with the analogue sound wave
- Measure its height at regular intervals
- Store each measurement as a binary number
- Play the samples back to recreate the sound
Complete the rules
A sound wave that varies smoothly is _____. Measuring the wave at regular moments is _____. The number of samples taken each second is the sample _____. The number of bits used for each sample is the sample _____.
Spot what enlarges the file
Tap the TWO things that make a sound file bigger.
- using a higher sample rate
- using more bits per sample
- taking fewer samples
- using a lower resolution
Make the call
Read each case and choose the best answer.
- A studio records music at a very high sample rate. What is the effect?
- How does a computer turn a real sound wave into numbers?
- You need a small sound file and do not mind lower quality. What do you do?
Explain digital sound
Explain how sound is stored digitally and how to calculate a sound file size.
- Explain what sampling, sample rate and resolution are
- Explain how to calculate a sound file size
- Explain how rate and resolution affect quality and size