What does the Edexcel principles of sound module cover?

It covers sound as a longitudinal pressure wave with amplitude (loudness), frequency (pitch), period and wavelength linked by the wave equation $v = f\lambda$, the decibel as a logarithmic ratio (the power formula $10\log_{10}$ and the amplitude formula $20\log_{10}$), the harmonic series and how relative harmonic levels create timbre, and the digital fundamentals of analogue-to-digital conversion, the Nyquist sampling theorem, aliasing, bit depth and dynamic range.

Which calculations recur most in this module?

The wave equation $v = f\lambda$ and the period $T = \frac{1}{f}$, the decibel formulae ($10\log_{10}$ for power and $20\log_{10}$ for amplitude or voltage), the Nyquist rule that the sampling rate must be at least twice the highest frequency, and dynamic range from bit depth at about $6$ dB per bit (so $16$-bit gives about $96$ dB and $24$-bit about $144$ dB).

Why is the decibel logarithmic?

Because human hearing responds to ratios, not absolute differences: each doubling of amplitude is heard as a similar step in loudness across an enormous range from the quietest audible sound to the threshold of pain. A logarithmic scale matches this perception and compresses that range into a manageable set of numbers. A doubling of amplitude is $+6$ dB, a doubling of power is $+3$ dB, and a perceived doubling of loudness is roughly $+10$ dB.

What is the most common mistake in this module?

Using the wrong decibel formula: amplitude and voltage ratios use $20\log_{10}$, while power and intensity ratios use $10\log_{10}$, and confusing them gives an answer out by a factor of two. A close second is saying the sampling rate must equal the highest frequency, when Nyquist requires it to be at least double, and confusing sampling rate (which sets the highest frequency captured) with bit depth (which sets the dynamic range).

How should I revise this module?

Learn the wave quantities and the wave equation cold, then drill the decibel formulae until choosing between $10\log_{10}$ and $20\log_{10}$ is automatic. Learn the harmonic series and the waveform shapes (sine, sawtooth, square, triangle) and their harmonic content, then master the digital fundamentals: Nyquist, aliasing, bit depth and dynamic range, with the standard resolutions ($44.1$ kHz / $16$-bit for CD, $48$ or $96$ kHz / $24$-bit for production).

EnglandMusic Technology

Edexcel A-Level Music Technology The principles of sound: a complete overview of amplitude, frequency, the decibel and digital audio

A deep-dive Edexcel A-Level Music Technology guide to the principles of sound. Covers amplitude, frequency, period and wavelength, the decibel as a logarithmic ratio, the harmonic series and timbre, and the digital fundamentals of sampling rate and bit depth, with the calculations and exam patterns Edexcel repeats in Component 3.

Generated by Claude Opus 4.816 min read9MT0Updated 2026-06-02

Reviewed by: AI editorial process; not yet individually human-reviewed

Jump to a section

What this module actually demands
Describing sound and the decibel
Timbre and digital audio
How this module is examined
Check your knowledge

What this module actually demands

The principles of sound is the technical foundation of the whole course. It covers how a sound wave is described, how the decibel measures level, how the harmonic series creates timbre, and how sound is digitised. The examiners test definitions, short calculations, and the ability to apply these ideas to real production decisions in Component 3.

This guide walks through the topics in order and sets out the exam patterns Edexcel repeats. Each topic has a matching dot-point page; this overview ties them together.

Describing sound and the decibel

Amplitude, frequency and wavelength treats sound as a longitudinal pressure wave: amplitude sets loudness, frequency sets pitch (a $2:1$ ratio is an octave), and period $T = \frac{1}{f}$ and wavelength $\lambda$ are linked by the wave equation $v = f\lambda$ (the speed of sound in air is about $340$ m per second). The audible range is roughly $20$ Hz to $20$ kHz. The decibel and loudness measures level as a logarithmic ratio: power ratios use $10\log_{10}$ and amplitude or voltage ratios use $20\log_{10}$ , so a doubling of amplitude is $+6$ dB and a doubling of power is $+3$ dB. In digital audio $0$ dBFS is the clipping ceiling, and dynamic range is the gap between the loudest and quietest usable levels.

Timbre and digital audio

Harmonics and timbre explains why instruments sound different: a periodic sound is a fundamental plus harmonics at integer multiples, and the relative levels of those harmonics create timbre (sine = pure, sawtooth = all harmonics, square = odd harmonics, triangle = mellow). Sampling rate and bit depth covers analogue-to-digital conversion: the Nyquist theorem (the sampling rate must be at least twice the highest frequency, so CD uses $44.1$ kHz), aliasing and the anti-aliasing filter, and bit depth setting the dynamic range at about $6$ dB per bit.

How this module is examined

A typical Edexcel profile:

Calculations. Period and wavelength from the wave equation, decibel gains and ratios, the minimum sampling rate from Nyquist, and dynamic range from bit depth.
Definitions. Amplitude versus frequency, the harmonic series, timbre, and dBFS and headroom.
Application. Why a $44.1$ kHz sample rate captures the audible band, why $24$ -bit recording gives more headroom, and why a sawtooth is a rich synthesis source.
Explanation. Why the decibel is logarithmic, and why aliasing must be prevented.

Check your knowledge

A mix of recall and calculation questions covering the module. Attempt them under timed conditions, then check against the solutions.

State the wave equation and define each term. (2 marks)
A note has a period of $2.0$ ms. Find its frequency. (1 mark)
State the decibel formula for an amplitude ratio. (1 mark)
By how many decibels does the level change if the amplitude is doubled? (1 mark)
A recording must capture frequencies up to $20$ kHz. State the minimum sampling rate. (1 mark)
State the approximate dynamic range of a $24$ -bit recording. (1 mark)

Solutions

Six short questions covering the principles of sound module.

Step 1: Q1 - The wave equation and its terms

The wave equation links three fundamental properties of a wave. Speed is measured in metres per second, frequency in hertz and wavelength in metres, and any one can be found if the other two are known.

v = f\lambda

Wave speed equals frequency times wavelength.

Final answer: $v = f\lambda$ , where $v$ is wave speed in m/s, $f$ is frequency in Hz, and $\lambda$ is wavelength in m.

Step 2: Q2 - Frequency from period

Period and frequency are reciprocals of each other. Converting the period from milliseconds to seconds first is essential before taking the reciprocal.

f = \frac{1}{T} = \frac{1}{0.0020} = 500\,\text{Hz}

Final answer: $500\,\text{Hz}$ .

Step 3: Q3 - Decibel formula for an amplitude ratio

The decibel is a logarithmic measure of a ratio. Amplitude and voltage ratios use the factor of $20$ in front of the logarithm, not $10$ , because power is proportional to amplitude squared.

\text{dB} = 20\log_{10}\!\left(\frac{A_2}{A_1}\right)

Final answer: $\text{dB} = 20\log_{10}\!\left(\dfrac{A_2}{A_1}\right)$ .

Step 4: Q4 - Level change when amplitude doubles

Doubling the amplitude means the ratio $A_2/A_1 = 2$ . Applying the amplitude decibel formula with this ratio gives the standard result that every doubling of amplitude adds approximately $6\,\text{dB}$ .

20\log_{10}(2) \approx +6\,\text{dB}

Final answer: $+6\,\text{dB}$ .

Step 5: Q5 - Minimum sampling rate from Nyquist

The Nyquist theorem states that the sampling rate must be at least twice the highest frequency to be captured. For audio extending to $20\,\text{kHz}$ , the minimum rate is therefore $40\,\text{kHz}$ .

f_s \geq 2 \times 20\,\text{kHz} = 40\,\text{kHz}

Final answer: At least $40\,\text{kHz}$ .

Step 6: Q6 - Dynamic range of a $24$ -bit recording

Each additional bit of depth roughly doubles the number of quantisation levels, adding approximately $6\,\text{dB}$ of dynamic range. With $24$ bits, the total dynamic range is approximately $24 \times 6\,\text{dB}$ .

\text{Dynamic range} \approx 24 \times 6 = 144\,\text{dB}

Final answer: Approximately $144\,\text{dB}$ .

Sources & how we know this

Pearson Edexcel A-Level Music Technology (9MT0) specification — Pearson Edexcel (2017)