How do additive, FM and wavetable synthesis build sounds differently from subtractive synthesis?
Other synthesis methods: additive synthesis (building from sine waves), FM synthesis (carrier and modulator), wavetable synthesis, the characteristic sounds of each, and how they contrast with subtractive synthesis.
A focused answer to the Edexcel 9MT0 synthesis content, covering additive synthesis from sine waves, FM synthesis with carrier and modulator, wavetable synthesis, their characteristic sounds, and the contrast with subtractive synthesis.
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What this dot point is asking
Edexcel wants you to know the synthesis methods beyond subtractive: additive (building from sine waves), FM (frequency modulation with carrier and modulator), and wavetable. You must explain how each generates a sound, the timbres each is known for, and how they contrast with subtractive synthesis. Recognising these methods by their characteristic sounds is examined in Component 3, and they are creative tools for Component 2.
The answer
Additive synthesis
It gives precise, independent control of every harmonic, which suits recreating complex or evolving tones such as organ and bell sounds. The drawback is that controlling dozens of harmonics by hand is laborious, the opposite trade-off to subtractive synthesis.
FM synthesis
FM is known for bright, metallic, bell-like, clangorous and electric-piano timbres, and punchy basses, because it readily creates the rich and often inharmonic spectra those sounds need. The Yamaha DX7 made FM hugely influential in the 1980s.
Wavetable synthesis
Contrasting the methods
The methods differ in how they create harmonic content. Subtractive removes harmonics from a rich source; additive adds harmonics from nothing; FM generates harmonics by modulation; wavetable changes the source waveform over time. Sample-based synthesis (covered separately) uses recorded sounds as the source. Knowing the typical sound of each lets you identify a synthesis method by ear.
Examples in context
When a track has a glassy electric piano or a clangorous bell, FM synthesis is likely behind it. When an organ-like or additive-pad tone has precisely controlled harmonics, additive synthesis may be the source. When a modern synth lead morphs and evolves continuously, wavetable scanning is at work. Recognising these methods by ear and explaining how they work is exactly what the analysis papers reward.
Try this
Q1. How does additive synthesis build a sound? [2 marks]
- Cue. By adding many sine waves, one per harmonic, at chosen frequencies and amplitudes.
Q2. In FM synthesis, what do the carrier and modulator do? [2 marks]
- Cue. The modulator varies the frequency of the carrier at audio rate, adding sidebands.
Q3. What timbres is FM synthesis known for? [1 mark]
- Cue. Bright, metallic, bell-like and electric-piano sounds.
Exam-style practice questions
Practice questions written in the style of Pearson Edexcel exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Edexcel 9MT0/03 20204 marksExplain the difference between additive synthesis and subtractive synthesis, and describe the kind of sound each is suited to producing.Show worked answer →
Additive synthesis builds a sound up by adding together many simple waveforms, usually sine waves, each at a chosen frequency and amplitude, so the harmonic content is assembled harmonic by harmonic from nothing. Subtractive synthesis works the opposite way: it starts with a harmonically rich waveform and removes (filters out) frequencies to shape the tone.
Additive synthesis gives precise control over the exact harmonic content and the ability to make each harmonic evolve independently, so it suits the careful recreation of complex or evolving timbres such as organ and bell-like tones, though it can be laborious. Subtractive synthesis is faster and more intuitive and suits the typical bright, filtered electronic sounds (basses, leads, pads).
Markers reward additive = adding sine waves to build harmonics, subtractive = filtering a rich wave, and a sensible suited-sound for each.
Edexcel 9MT0/03 20234 marksDescribe how FM (frequency modulation) synthesis creates a sound, referring to the carrier and modulator, and state the kind of timbres it is known for.Show worked answer →
FM synthesis creates sounds by using one oscillator (the modulator) to rapidly modulate the frequency of another oscillator (the carrier) at audio rate. This modulation adds new frequencies (sidebands) to the carrier, generating complex harmonic and inharmonic content that depends on the ratio of the carrier and modulator frequencies and the amount (depth) of modulation.
FM synthesis is known for bright, metallic, bell-like, clangorous and electric-piano timbres, as well as punchy basses, because it can easily produce the rich, often inharmonic spectra characteristic of those sounds. It became famous through the Yamaha DX7.
Markers reward one oscillator modulating another's frequency, the carrier and modulator (sidebands/ratio/depth), and the metallic, bell-like, electric-piano timbres FM is known for.
Related dot points
- Subtractive synthesis: oscillators and waveforms, the voltage-controlled signal path (VCO, VCF, VCA), the filter and resonance, the ADSR envelope, the LFO and modulation, and how these combine to design a synth sound.
A focused answer to the Edexcel 9MT0 subtractive synthesis content, covering oscillators and waveforms, the VCO, VCF and VCA signal path, the filter and resonance, the ADSR envelope, the LFO and sound design.
- Sampling and sample-based synthesis: capturing and triggering samples, the sampler and key mapping, looping, time-stretching and pitch-shifting, slicing and reordering, warping to tempo, and creative sample manipulation.
A focused answer to the Edexcel 9MT0 sampling content, covering capturing and triggering samples, the sampler and key mapping, looping, time-stretching, pitch-shifting, slicing and reordering, and creative manipulation.
- MIDI and sequencing: MIDI as performance data not audio, note, velocity and controller messages, real-time and step input, quantisation and groove, programming drums and instruments with velocity and timing for a realistic result.
A focused answer to the Edexcel 9MT0 MIDI content, covering MIDI as performance data versus audio, note, velocity and controller messages, real-time and step input, quantisation and groove, and programming realistic parts.
- The harmonic series and timbre: fundamental and harmonics, how the relative levels of harmonics shape tone, the waveform shapes of basic tones, the frequency spectrum and the phase relationships that create a sound's character.
A focused answer to the Edexcel 9MT0 harmonics content, covering the harmonic series, fundamental and harmonics, how relative harmonic levels shape timbre, the basic waveform shapes, the frequency spectrum and phase.
- The digital revolution: the move from analogue to digital audio, the compact disc (1982), MIDI (1983), the digital sampler, hard-disk recording and the rise of the DAW, and software pitch correction such as Auto-Tune.
A focused answer to the Edexcel 9MT0 digital history, covering the move from analogue to digital, the compact disc (1982), MIDI (1983), the digital sampler, hard-disk recording, the DAW, and Auto-Tune.
Sources & how we know this
- Pearson Edexcel A-Level Music Technology (9MT0) specification — Pearson Edexcel (2017)