Analog synthesizers are the backbone of electronic music, shaping sounds through a series of interconnected modules. These modules work together to create, shape, and modulate audio signals, allowing for endless sonic possibilities.

Understanding the signal flow and architecture of analog synths is crucial for crafting unique sounds. From oscillators generating initial waveforms to filters shaping timbre and amplifiers controlling volume, each component plays a vital role in the final output.

Analog Synthesizer Architecture and Signal Flow

Signal flow in analog synthesizers

• Oscillators generate the initial waveforms (sawtooth, square, triangle, sine) that determine the pitch of the sound
• Filters modify the timbre of the oscillator waveforms by attenuating or boosting specific frequency ranges
  • Common filter types include low-pass (removes high frequencies), high-pass (removes low frequencies), band-pass (allows a specific frequency range to pass through), and notch (removes a specific frequency range)
  • Filters are controlled by cutoff frequency (determines the point at which frequencies are attenuated) and resonance (emphasizes frequencies around the cutoff point) parameters
• Amplifiers control the volume of the sound and are shaped by an envelope generator
  • ADSR (Attack, Decay, Sustain, Release) envelopes define the volume contour over time
    • Attack: time taken for the sound to reach its maximum level
    • Decay: time taken for the sound to drop from the maximum level to the sustain level
    • Sustain: level at which the sound remains while the key is held down
    • Release: time taken for the sound to fade out after the key is released
• Modulation sources, such as low-frequency oscillators (LFOs) and envelope generators, create movement and variation in the sound by modulating pitch, filter cutoff, amplifier volume, and other parameters

Common modules and interconnections

• Voltage-controlled oscillators (VCOs) generate the basic waveforms, and their pitch can be modulated by control voltages from keyboards, sequencers, or other modules
• Voltage-controlled filters (VCFs) shape the frequency spectrum of the oscillator waveforms, with cutoff frequency and resonance modulated by control voltages
• Voltage-controlled amplifiers (VCAs) adjust the volume of the sound and are controlled by envelope generators or other modulation sources
• Envelope generators (EGs) create time-varying control voltages for shaping the sound, with the most common being ADSR (Attack, Decay, Sustain, Release)
• Low-frequency oscillators (LFOs) generate slow, periodic control voltages for modulation, creating effects like vibrato (pitch modulation) and tremolo (volume modulation)
• Patch bay or matrix allows for flexible routing of audio and control signals between modules, enabling complex and creative sound design

Creative Patching and Sound Design

Block diagrams of classic synthesizers

• Moog Minimoog features three VCOs, one VCF, two EGs, and a noise source in a fixed signal path with limited modulation options, known for its rich, thick bass sounds and lead tones
• ARP Odyssey includes two VCOs, a duophonic keyboard, a sample-and-hold circuit, and a ring modulator, with a unique lowpass/highpass filter combination capable of producing complex, evolving sounds
• Sequential Circuits Prophet-5 introduced the concept of programmable synthesizers with five voice polyphony, each voice containing two VCOs, a VCF, and an ADSR envelope, along with patch memory for storing and recalling sounds

Custom patch creation techniques

1. Experiment with different oscillator waveforms and combinations

   • Mix sawtooth and square waves for rich, complex timbres
   • Detune oscillators slightly for chorusing and thickening effects (e.g., a lush pad sound)

2. Use filters to shape the frequency spectrum

   • Lowpass filters for smooth, mellow sounds (e.g., warm bass or soft lead)
   • Highpass filters for thin, bright tones (e.g., percussive or airy sounds)
   • Bandpass filters for emphasizing specific frequency ranges (e.g., vowel-like or nasal tones)
   • Resonance for adding character and emphasis (e.g., squelchy bass or whistling lead)

3. Modulate parameters with LFOs and envelope generators

   • Route an LFO to oscillator pitch for vibrato (e.g., a singing or flute-like sound)
   • Use an envelope generator to control filter cutoff for dynamic timbral changes (e.g., a plucky or percussive sound)
   • Modulate VCA with an envelope for shaping the volume contour (e.g., a punchy bass or a slowly evolving pad)

4. Explore unconventional patching techniques

   • Feedback loops: Route the output of a module back into its input for complex, chaotic sounds (e.g., screaming or metallic tones)
   • Cross-modulation: Use one oscillator to modulate the pitch or pulse width of another for complex harmonics (e.g., bell-like or dissonant timbres)
   • Self-oscillating filters: Push the resonance of a filter to create a sine-like tone that can be played melodically or used as an additional oscillator (e.g., a pure, ethereal sound)