Questions: Electronic Sound Design and Synthesis in Composition

Question 1

A composer wants a sound that begins as a single pure tone and gradually accumulates timbral complexity over 30 seconds. Which synthesis method is best suited for this goal, and why?

• A. Subtractive — progressively close a high-pass filter to roll off the upper harmonics over time
• B. Granular — fragment the source tone into grains and reassemble them for cloud-like texture
• C. Additive — begin with one sine wave at the fundamental and progressively layer in harmonics at controlled amplitudes and rates
• D. FM synthesis — the only method that supports timbral evolution over long time spans

Answer: (C)

Additive synthesis builds timbre by summing sine waves, giving direct control over which harmonics are present and at what amplitude. Starting with only the fundamental and gradually fading in partials over 30 seconds directly enacts the desired evolution. Subtractive synthesis starts with a rich waveform and removes frequencies — well-suited for brightening or darkening, but requires a rich source to begin with. Granular synthesis creates cloud-like textures from fragmented samples, which serves a different purpose.

Question 2

A synthesizer's ADSR envelope is set to: Attack = 1ms, Decay = 50ms, Sustain = 0, Release = 0. What character will this envelope give to a sound?

• A. A slow, atmospheric pad that swells gradually and fades over several seconds
• B. A sharp percussive transient — a short click or pluck that rises and dies almost instantly with no sustained body
• C. A bowed-string quality with a long held note and smooth release
• D. A tremolo effect with rhythmic amplitude oscillation

Answer: (B)

With near-zero attack (immediate peak), fast decay (rapid fall from peak), zero sustain (nothing held), and zero release (instant cut after key release), the sound is essentially a very brief spike — the envelope shape of a plucked string, drumstick hit, or percussive click. The ADSR shape is the sonic fingerprint of how a sound evolves over time; mastering it means you can predict and design the feel of a sound by its envelope alone, before even choosing a waveform.

Question 3

In subtractive synthesis, sweeping a low-pass filter's cutoff frequency downward (toward lower frequencies) will make the sound progressively darker and more bass-heavy.

• T. True
• F. False

Answer: True

A low-pass filter lets frequencies below the cutoff through and attenuates those above it. Sweeping the cutoff downward removes more and more high-frequency harmonics from the waveform, leaving only the fundamental and lowest partials — which the ear perceives as a darker, warmer, more bass-heavy tone. This timbral evolution through filter sweeping is the defining sound of classic subtractive synthesis (e.g., the Moog filter sweep). The raw sawtooth or square wave contains all these harmonics; the filter sculpts the timbre by selectively removing them.

Question 4

Microtonality — pitches between the standard twelve equal-tempered semitones — is primarily an acoustic phenomenon and is difficult to achieve in electronic synthesis, which is generally locked to the standard keyboard grid.

• T. True
• F. False

Answer: False

This is precisely backwards. Electronic synthesis makes microtonality trivially easy: you simply specify a frequency in Hz rather than selecting a MIDI note from the 12-tone grid. A standard acoustic piano cannot produce the pitch between A4 (440 Hz) and A#4 (466 Hz), but a synthesizer can produce 450 Hz or 442.7 Hz or any arbitrary frequency with equal ease. Electronic music opens harmonic worlds — just intonation, 19-tone equal temperament, invented tuning systems — that are essentially inaccessible on conventional instruments. Microtonality is one of the defining freedoms of electronic composition.

Question 5

How does the ADSR envelope transform timbre from a fixed property of a sound into a dynamic compositional parameter? Give a concrete example of applying an envelope to filter cutoff rather than amplitude, and describe the musical result.

Model answer: The ADSR envelope controls how a parameter changes over time — not just its final value. Applied to amplitude, it shapes the volume arc of a note. Applied to filter cutoff, it makes the timbral brightness itself evolve. For example: a synthesizer bass patch with a fast-attack, fast-decay envelope on the filter cutoff will momentarily open the filter (adding bright harmonics) at the moment a key is struck, then quickly close it back to a dark sustained tone. The result is the characteristic 'vowel-like' wah quality of many classic bass sounds — the timbre momentarily flares bright at the attack transient, then settles into a darker body, mimicking the behavior of acoustic instruments where the attack transient is spectrally richer than the sustained tone.

This example illustrates the key principle: in electronic synthesis, timbre is not fixed at design time but can be programmed to evolve across the duration of each note, across a phrase, or across an entire piece. An acoustic composer orchestrates timbre by choosing instruments; an electronic composer writes the timbral trajectory itself.