A synthesizer is an electronic instrument that builds sound from electrical signals instead of vibrating strings, air columns, or drumheads. When a player presses a key, the synth turns that action into instructions for pitch, loudness, and timing. This matters because the same basic signal path can imitate familiar instruments or create sounds that do not exist acoustically.
Understanding a synthesizer connects music to waves, frequency, circuits, and digital control.
A typical subtractive synthesizer starts with an oscillator that produces a repeating waveform such as a sine, square, sawtooth, or triangle wave. The signal then passes through a filter that removes or emphasizes certain frequencies, an amplifier that shapes loudness over time, and effects that add space, motion, or texture. Finally, a speaker converts the changing electrical signal into changing air pressure, which the ear detects as sound.
For example, a bright sawtooth wave can be filtered and shaped with a quick attack to make a sharp electronic bass note.
Key Facts
- Frequency controls pitch: higher frequency means higher pitch.
- For equal-tempered tuning, f = 440 x 2^(n/12), where n is the number of semitones from A4.
- A waveform's shape affects timbre because it changes the mix of harmonics.
- A filter changes tone by boosting or reducing selected frequency ranges.
- A low-pass filter lets low frequencies pass and reduces high frequencies above the cutoff frequency.
- An amplifier envelope often uses ADSR: attack, decay, sustain, and release to shape loudness over time.
Vocabulary
- Oscillator
- An oscillator is a circuit or program that creates a repeating electrical waveform at a chosen frequency.
- Waveform
- A waveform is the shape of a repeating signal, such as a sine, square, triangle, or sawtooth wave.
- Filter
- A filter is a module that changes a sound by reducing or emphasizing certain frequencies.
- Envelope
- An envelope is a time pattern that controls how a sound parameter, usually loudness, changes after a key is pressed and released.
- Timbre
- Timbre is the quality or tone color that makes two sounds with the same pitch and loudness seem different.
Common Mistakes to Avoid
- Confusing pitch with loudness: pitch depends mainly on frequency, while loudness depends mainly on amplitude.
- Thinking a synthesizer only makes digital sounds: many synthesizers use analog electrical circuits, and both analog and digital synths can create rich musical tones.
- Assuming the oscillator alone makes the final sound: the filter, amplifier envelope, and effects strongly shape the tone that reaches the speaker.
- Setting cutoff frequency without listening to harmonics: lowering a low-pass cutoff removes high-frequency harmonics, which can make a sound darker or softer.
Practice Questions
- 1 A synthesizer oscillator is set to A4 at 440 Hz. What is the frequency of the note one octave above it?
- 2 Using f = 440 x 2^(n/12), find the frequency of the note 12 semitones below A4. Round to the nearest hertz.
- 3 A patch uses a sawtooth oscillator, a low-pass filter, a fast attack, and a short release. Explain why this could sound like a bright plucked or bass sound rather than a smooth flute-like sound.