How do you design sounds from synthesis and use virtual instruments in a production?
Synthesis methods (subtractive, FM, wavetable and sampling), the synth signal path (oscillators, filters, envelopes and LFOs), and programming and sequencing virtual instruments with MIDI.
An SQA Advanced Higher Music Technology answer on synthesis and virtual instruments, covering subtractive, FM, wavetable and sample-based synthesis, the oscillator-filter-amplifier path with envelopes and LFOs, and how MIDI sequencing and virtual instruments are programmed in a production.
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What this skill is asking
The SQA wants you to design sounds with synthesis and use virtual instruments in a production: understanding the main synthesis methods, knowing the signal path of a synthesiser, and programming and sequencing with MIDI. At Advanced Higher you are expected to create and shape your own sounds, not just play presets, which is why this skill underpins contexts such as advanced synthesis and composing with virtual instruments.
Synthesis methods
Each method creates sound differently. Subtractive synthesis, the most common starting point, begins with a harmonically rich waveform and removes harmonics with a filter, which is intuitive and great for classic analogue-style sounds. FM (frequency modulation) uses the output of one oscillator to modulate the frequency of another, producing complex, often metallic or bell-like timbres that subtractive synthesis cannot easily make. Wavetable synthesis stores a table of waveforms and moves through them over time, giving distinctive evolving textures. Sampling is different again: it plays back recorded audio, which makes it the realistic choice for acoustic instruments. Choosing the right method for the sound you want is an Advanced Higher decision.
The synthesiser signal path
Understanding the signal path lets you predict and design a sound. Oscillators generate the raw waveform (sine, sawtooth, square, triangle), each with a characteristic harmonic content. The filter, usually a low-pass with a cutoff and resonance, removes or emphasises harmonics to set the brightness and character. The amplifier sets the loudness over time. The two key modulators are the envelope, most often an ADSR shaping the amplifier or the filter so the sound starts, sustains and ends as you want, and the low-frequency oscillator (LFO), which sweeps a parameter (pitch for vibrato, filter for a wah, amplitude for tremolo) to add movement. Programming these is how a raw oscillator becomes a usable, expressive sound.
Virtual instruments and MIDI
Modern productions rely on virtual instruments, software versions of synthesisers and samplers that run inside the digital audio workstation. They are played and sequenced with MIDI, a protocol that transmits performance information such as which note, how hard (velocity), and controller movements, rather than the sound itself. Because MIDI is data, a sequenced part can be quantised, transposed, re-voiced or re-instrumented without re-recording, and the same MIDI can drive a piano now and a synth later. This flexibility is exactly why the course lists composing with virtual instruments as a suitable production context.
Examples in context
A synth bass for an electronic track is built subtractively: a sawtooth oscillator, a low-pass filter with a short filter envelope for punch, and a fast amplitude envelope for a tight note. A film pad uses detuned oscillators, a slow attack and a slow filter sweep for an evolving bed. An orchestral mock-up uses sampled virtual instruments, with carefully edited velocity, timing and controllers to sound like real players. Each shows the same skill: choosing a method and programming the parameters to get a specific sound.
Try this
Q1. State what the filter does in a subtractive synthesiser. [1 mark]
- Cue. It removes or emphasises harmonics to shape the tone (brightness).
Q2. State what the four stages of an ADSR envelope are. [1 mark]
- Cue. Attack, decay, sustain and release.
Q3. State what kind of information MIDI carries. [1 mark]
- Cue. Performance data (note, velocity, controllers), not audio.
Exam-style practice questions
Practice questions written in the style of SQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
SQA AH style6 marksDescribe the signal path of a subtractive synthesiser and explain how you would use the oscillators, filter and envelopes to create an evolving pad sound.Show worked answer →
In subtractive synthesis the path runs oscillator to filter to amplifier, with envelopes and LFOs as modulators. The oscillators generate harmonically rich raw waveforms (for example sawtooth or square). The filter, usually a low-pass, removes harmonics to shape the tone. The amplifier sets the level over time, controlled by an envelope.
To create an evolving pad, use two or more detuned oscillators on a rich waveform such as sawtooth, which gives a wide, full sound. Set the amplitude envelope with a slow attack and a long release so the sound fades in gently and tails off rather than starting abruptly. Apply a filter envelope (or an LFO on the filter cutoff) with a slow movement so the brightness opens and closes over time, giving the pad its evolving quality. A slow LFO on pitch or filter adds gentle movement, and reverb completes the lush, sustained character.
Markers reward a correct oscillator to filter to amplifier path, the use of rich detuned oscillators, a slow-attack long-release amplitude envelope, and filter movement (filter envelope or LFO) to create the evolving, sustained pad.
SQA AH style4 marksExplain the difference between subtractive synthesis and sample-based (sampler) virtual instruments, and give one advantage of each.Show worked answer →
Subtractive synthesis starts with harmonically rich waveforms generated by oscillators and shapes the sound by filtering out (subtracting) harmonics, then shaping level and movement with envelopes and LFOs. The sound is created from scratch electronically.
A sample-based virtual instrument plays back recordings (samples) of real instruments or sounds, mapped across the keyboard and triggered by MIDI, often with multiple velocity layers for realism.
One advantage of subtractive synthesis is total creative control: you can design original sounds that do not exist acoustically and shape every parameter. One advantage of a sampler is realism: because it plays real recordings, it can reproduce acoustic instruments far more convincingly than a synthesiser can model them.
Markers reward a correct contrast (oscillators and filtering versus playback of recorded samples) and one valid advantage for each (creative control and original sounds for synthesis; realism and authentic acoustic timbres for sampling).
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