Technologies K–10 · Years 7–8

Sampling sound: sample rate, bit depth and file size

Digital Technologies context (NSW Technology Mandatory 7–8, 2017, outgoing; the Technology 7–8 Syllabus (2023) Digital and communication technologies focus area has no content point on data representation); Digital Technologies: Knowledge and understanding, Data representation (ACARA v9)

Practical, model not builtLow risk

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The idea

Sound is stored as a stream of integer samples, so a file's size is samples per second × bits per sample × channels × seconds, and the highest pitch it can hold is half the sample rate.

What you need

Computer with Audacity and headphones
File Explorer showing file size in bytes

How to do it

In Audacity, generate a 10-second tone at 1000 Hz.
Export it as WAV, 44,100 Hz, 16-bit, stereo. Predict and then read the file size.
Change the project to 8000 Hz, mono, and export as 8-bit WAV. Predict and read the size again.
Generate a 6000 Hz tone at 44,100 Hz, listen at low volume, then resample to 8000 Hz and listen again.
Zoom in on the waveform until single samples show as dots, and count the samples in 1 ms at each rate.
Decide which settings suit a phone call and which suit music, giving the numbers.

What you should see

44,100 samples × 16 bits × 2 channels = 1,411,200 bits per second = 176,400 bytes per second, so 10 seconds is 1,764,000 bytes of samples plus the header (44 bytes for a plain WAV header, more if the program adds tags). At 8000 Hz, 8 bits, mono, 10 seconds is 80,000 bytes of samples. The highest pitch storable is 22,050 Hz at 44,100 Hz and 4000 Hz at 8000 Hz, so the 6000 Hz tone cannot survive resampling to 8000 Hz: the resampler filters it out, and without that filter it would come back as a false 2000 Hz tone. In 1 ms there are 44.1 samples at 44,100 Hz and 8 at 8000 Hz. The learner knows it worked when predicted sizes match the files to within the header bytes.

What changes

This activity lists no variables to change, measure and keep the same.

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

A higher sample rate makes sound louder (it records higher pitches and more detail).
Digital audio stores the sound wave itself (it stores numbers measured many times a second).
Any sample rate can record any pitch (pitches above half the rate are lost or distorted).

Safety card

Low riskLearners carry it out

Hazards

Loud tones through headphones

Controls

Set the volume low before playing any tone

Note

No chemicals or heat.

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

Technology Mandatory 7–8 Syllabus (2017), NESA. Outgoing: replaced by the Technology 7–8 Syllabus (2023) from 2026 and not available after December 2027. Code read from the official syllabus document (DOCX) on 2026-09-22.TE4-7DI
Australian Curriculum v9AC9TDI8K03

Sources

The pages the author read to write this activity.

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