Kretz FM Synthesizer: Documentation

Welcome to the official documentation for the Kretz FM Synthesizer. This guide provides a detailed and comprehensive overview of every feature, from the fundamentals of its sound engine to advanced sequencing, effects processing, and project management.

1. Introduction & What to Expect

The Kretz FM Synthesizer is a powerful, browser-based instrument that combines the unique timbral possibilities of Frequency Modulation (FM) synthesis with the familiar workflow of a traditional subtractive synthesis signal path. It's designed to be both an educational tool and a capable instrument for creating music.

• What is FM Synthesis? At its core, FM synthesis creates complex timbres by using one oscillator (the Modulator) to rapidly modulate the frequency of another audible oscillator (the Carrier). Imagine one person's voice causing another's to waver, but thousands of times per second. This technique is famous for producing rich, dynamic sounds—from glassy bells and vibrant electric pianos to aggressive, metallic textures that are difficult to achieve with other synthesis types.

• What You Can Do: This synthesizer is designed to be a versatile tool for sound design and music creation. You can:

  • Craft intricate and evolving sounds from scratch (e.g., sharp basslines, shimmering pads, complex sound effects) using the powerful FM engine, filter, and LFO.

  • Build complex melodic and rhythmic patterns with the intuitive but powerful step sequencer, complete with per-step parameter automation.

  • Polish your sound with a built-in suite of high-quality effects, including distortion, chorus, delay, and reverb.

  • Save, load, and even render your full creations as pristine audio files directly from the browser, perfect for use in other projects.

2. Getting Started

Before you can begin, the synthesizer's audio engine must be activated. This is a standard security requirement for web audio applications to ensure audio only plays with user consent.

1. When you first load the page, you will see the "Welcome" screen.

2. Click the Start Synthesizer button.

3. The application will initialize the audio components, and the main interface will appear. The "Audio Status" indicator in the top-right corner should turn green and read Audio: running. If it fails, try refreshing the page or using a modern browser like Chrome or Firefox.

3. The Synthesis Engine

The left panel contains all the controls for shaping your sound. The signal flows logically from the oscillators (Carrier and Modulator), through the filter, and then to the final effects chain.

Global Controls

These controls affect the overall behavior and response of the synth patch.

• Random Sound: Instantly generates a new, randomized sound by adjusting most synthesis parameters. This is a fantastic way to discover new sonic possibilities or to find a creative starting point. If you find something you like, save it as a project and then tweak it to perfection!

• Master Pitch: Transposes the entire synthesizer up or down in semitones (st). The range is from -12 (one octave down) to +12 (one octave up).

• Master Volume: Sets the final output level of the instrument in decibels (dB). Keep an eye on the meter to ensure the signal isn't clipping.

• Output Level Meter: This visual meter shows the volume of the sound leaving the synthesizer. If it's consistently hitting 100%, reduce the Master Volume to avoid unwanted digital distortion.

• Portamento: Also known as "glide." This sets the time it takes for the pitch to slide smoothly from one note to the next. A value of 0.0s means no glide. Higher values are great for legato-style leads and basslines.

Carrier Section

The Carrier is the primary oscillator; it's the part of the synth that produces the fundamental tone you hear.

• Waveform: Selects the fundamental shape of the Carrier oscillator's sound.

  • Sine, Square, Sawtooth, Triangle: Standard synthesis waveforms, from the pure tone of a Sine to the bright, buzzy Sawtooth.

  • Pulse: A square wave with variable width, controlled by the PWM knob.

  • PWM: A Pulse wave that is automatically modulated by an internal LFO, creating a classic, thick chorus-like effect. The PWM knob still sets the center width.

  • Noise: Replaces the Carrier oscillator with a white noise generator. When selected, the Modulator section disappears, as you cannot FM modulate noise. This is useful for creating percussive sounds like hi-hats and snares, or atmospheric effects like wind.

• PWM: (Pulse Width Modulation) This knob is only active when Pulse or PWM is selected. It adjusts the duty cycle (width) of the pulse wave, changing its timbre from thin and reedy to full and square-like.

• Carrier ADSR Envelope: This is the main amplitude envelope. It controls the volume of the sound over time from the moment a note is triggered. For example, to create a percussive "pluck" sound, use a fast Attack, a short Decay, zero Sustain, and a medium Release.

  • Attack: The time it takes for the sound to reach its maximum volume.

  • Decay: The time it takes for the sound to drop from its maximum level to the sustain level.

  • Sustain: The volume level the sound holds at as long as a note is held down.

  • Release: The time it takes for the sound to fade to silence after the note is released.

Modulator Section

The Modulator is the second oscillator. You don't hear it directly. Instead, it modulates the frequency of the Carrier, creating new harmonics (sidebands) and shaping the final timbre. This section is hidden when the Carrier Waveform is set to Noise.

• Waveform: Selects the shape of the Modulator oscillator. A Sine wave produces the cleanest, most classic FM tones. More complex waves like Square or Sawtooth introduce a wider, often harsher, set of harmonics.

• Mod Index (Modulation Index): This is the most important FM control. It determines how much the Modulator affects the Carrier's pitch. At low values (1-5), the effect is subtle, adding gentle harmonics. At high values (20+), it creates complex, bell-like, or even dissonant tones. This parameter can be automated on a per-step basis in the sequencer.

• Modulator ADSR Envelope: This envelope controls the Modulation Index over time. This is the key to creating dynamic, expressive sounds. For example, a fast attack and decay on this envelope will create a sharp, percussive transient at the start of a note, where the sound is briefly bright and metallic before settling into a simpler tone.

Filter & Filter Envelope

The filter shapes the tone of the sound by removing frequencies, just like in a subtractive synthesizer.

• Cutoff: Sets the frequency at which the filter begins to cut. For this lowpass filter, any frequencies above the cutoff point are progressively reduced in volume, making the sound darker or more muffled.

• Resonance: Boosts the frequencies right at the cutoff point. Lowering the cutoff while increasing the resonance can give the sound a "whistling" or "singing" quality.

• Filter Envelope (ADSR): This is a dedicated envelope that modulates the Filter Cutoff frequency over time.

  • Attack, Decay, Sustain, Release: These function just like the main amplitude envelope but control the filter's movement instead of volume.

  • Amount: This crucial control determines how much the envelope affects the cutoff frequency. A positive amount will cause the envelope to "open" the filter, making the sound brighter during the attack/decay phases. This is key for classic synth stabs, basses, and leads.

LFO (Low-Frequency Oscillator)

The LFO creates continuous, rhythmic modulation, adding movement and life to your sound.

• Waveform: The shape of the LFO's modulation cycle (e.g., a smooth sine wave or an abrupt square wave).

• Frequency: The speed of the LFO, measured in cycles per second (Hertz).

• Amount: The intensity or depth of the LFO's modulation.

• Target: Determines what parameter the LFO will modulate.

  • None: LFO is inactive.

  • Pitch: Creates a classic vibrato effect.

  • Filter: Creates a "wah-wah" or sweeping "wobble" bass effect.

  • Mod Index: Creates a rhythmic change in the sound's FM timbre, making it pulse between simple and complex tones.

4. Sequencer & Effects

The right panel is your command center for composition, automation, and final sound processing.

Project & Audio

• Save Project: Saves the entire state of the synthesizer—all knob positions, sequence data, and effects settings—into a single .krfm file for later use.

• Load Project: Opens a file dialog to load a previously saved .krfm file, instantly restoring your session.

• Render Sequence: This powerful feature renders the current sequence offline and downloads it as a high-quality .wav audio file. This is perfect for capturing a loop to use in a sampler or a Digital Audio Workstation (DAW).

The Sequencer

The step sequencer is the heart of the Kretz FM Synth. It allows you to program intricate patterns note by note with detailed control.

Sequencer Interaction - The Basics

• The Grid: The grid represents the steps in your sequence. Each column is one step that will play in order from left to right.

• Activate/Deactivate a Step:

  • Left-click on a step to toggle it on or off. An active step is brightly colored and will trigger a note.

  • Ctrl+Click (or Cmd+Click on Mac) to definitively deactivate a step.

• Change a Step's Note:

  • Click and drag vertically on any step to change its pitch. The note name is displayed inside the step for easy reference.

• Change a Step's Modulation Index (Per-Step Automation):

  • Hold Shift, then click and drag vertically on a step. This overrides the global Mod Index knob for that specific step. This is one of the most powerful features for creating evolving patterns. For example, you could have a high Mod Index on the first beat for emphasis, and lower values on other steps for a more subdued tone. The global Mod Index slider will update to show the value of the step you are currently editing.

Sequencer Controls

• Play / Stop: Starts and stops the sequencer playback.

• Tempo: Sets the playback speed in Beats Per Minute (BPM).

• Swing: Adds a "shuffle" feel to the rhythm. Subtle values can make a rigid 16th-note pattern feel more human and groovy.

• Length: Adjusts the number of steps in the sequence, from 2 to 32, allowing for simple loops or more complex phrases.

• Transpose: The - and + buttons shift the pitch of all notes in the sequence up or down by one semitone.

• Clear: Deactivates all steps in the sequence and resets any transposition.

• Randomize: Fills the sequencer with random notes and activations. Use this as a creative spark, then refine the generated pattern to your liking.

• Rand Mod: Assigns a random Modulation Index value to every step in the sequence.

• Clear Mod: Resets the per-step Modulation Index for all steps back to the global knob's current value.

• Clear Notes: Resets the pitch of every step to the default (C4) without changing their active/inactive state.

• Shift Left / Right (< / >): Rotates the entire sequence pattern one step to the left or right. This is excellent for creating instant rhythmic variations of your pattern.

Effects

The built-in effects are the final stage to add space, character, and polish to your sound. They are processed in series: Distortion -> Chorus -> Delay -> Reverb.

• Distortion: Adds grit, harmonics, and aggression.

  • Amount: Controls the intensity of the distortion effect.

  • Oversample: Improves the audio quality of the distortion, reducing unwanted digital artifacts called aliasing. 4x is recommended for the best sound.

• Chorus: Creates a thick, shimmering, stereo-widening effect.

  • Frequency: The speed of the chorus's internal LFO.

  • Depth: The intensity of the pitch modulation.

  • Spread: The stereo width of the effect. At 180, the effect is fully stereo.

  • Wet: The mix between the dry (unaffected) and wet (chorus) signal.

• Delay: Creates echoes or repeats of the sound.

  • Time: The delay time, which is automatically synced to the project's tempo.

  • Feedback: The number of times the sound repeats. High values can cause the echoes to build on each other infinitely.

  • Wet: The volume of the delay repeats.

  • Ping Pong Delay (Toggle): When on, the delay repeats will alternate between the left and right stereo channels.

• Reverb: Simulates the sound of a physical space, adding depth and ambience.

  • Decay: The time it takes for the reverb reflections to fade out. Longer times simulate a larger space.

  • Wet: The amount of reverb effect mixed into the final signal.

5. Keyboard Shortcuts

Boost your workflow with these handy keyboard shortcuts. Note that these are disabled when you are typing in a text input field to prevent accidental triggers.

• P: Play the sequence.

• S: Stop the sequence.

• Ctrl / Cmd + S: Save the current project.

• Ctrl / Cmd + L: Open the "Load Project" file dialog.

• Ctrl / Cmd + R: Render the current sequence to a .wav file.

Demo examples