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DESIGN_DOC.md

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Dropseed Design Document

Dropseed is an open source audio graph engine, plugin hosting engine, system IO, and a general purpose DAW (Digital Audio Workstation) engine. It's main purpose is to be the engine powering Meadowlark, but it can be used by other DAW projects and audio software that needs plugin hosting and/or an audio graph.

Objective

Why am I creating a new DAW Engine? Why not just use the Tracktion Engine?

Dropseed aims to have these key features over Tracktion:

  • Modular ecosystem: you only need to include the parts of the engine you use
  • Good documentation with examples
  • Written in Rust, with all the safety advantages that brings
  • Zero dependencies on JUCE
  • Completely independent of any GUI library
  • Ability to interface with the engine in a serialized channel, allowing you to run the engine in a separate process
  • Full first-class support for all of CLAP's features, allowing for some exciting new ways to use plugins
  • Better control over the engine: it doesn't force you to use a certain workflow
  • C bindings
  • Maybe MIT license? I haven't decided on that yet.

In addition, this is a passion project for me.

Goals

Audio Graph

  • A highly flexible and robust audio graph engine that lets you route anything anywhere (as long as it doesn't create a cycle)
  • Automatic summation
  • Automatic delay compensation
  • Automatic cycle detection
  • High performance multithreaded processing
  • Buffers and events are modeled after the CLAP spec, allowing it to take advantage of all of CLAP's features
  • Some included nodes such as gain, pan, phase invert, wet/dry mix, mono-to-stereo, stereo-to-mono, monitor, etc
  • Mixer node (includes gain, pan, mute, and phase invert for efficiency)
  • Macro node (for controlling a parameter on a plugin)
    • Ability to be assigned to multiple parameters and plugins
    • Per-parameter ranges and curves
  • Additional nodes such as stereo split, L/R split, and mulitband split
  • Ability to create your own nodes using a similar API to CLAP
  • (not MVP) Negative delay compensation
  • (not MVP) 64-bit audio buffers

Plugin Host

  • First-class support for the open source CLAP audio plugin standard
  • (not MVP) Support for LV2 and VST3 plugins via a CLAP bridge

System IO

  • Ability to enumerate and connect to system audio devices with low latency (including duplex support)
  • Ability to enumerate and connect to system MIDI devices
  • Robust error handling

DAW Engine

  • Transport
    • Multiple transports can exist in the same project
    • Loops
    • (not MVP) automated tempo
    • (not MVP) time signature changes
    • (not MVP) global swing
  • Audio clip player node
    • An audio clip player node can house any number of clips
    • Automatic loading, resampling, and caching of audio data (all audio clip player nodes share the same cache)
    • Fades and crossfades
    • Clips can be assigned to multiple transports, as well as multiple places within the same transport
    • Clips can be played solo without a transport
    • Clips can be disabled
    • Automatic transport declicking, including loops
    • Reverse
    • Retrieve optimized waveform data for drawing waveforms in the UI
    • (not MVP) Ability to create your own custom offline audio clip effects
    • Record into a new clip
      • Retrieve optimized waveform data for drawing waveforms in the UI
      • Result of recording is saved to disk
      • (not MVP) Audio is streamed to disk as a backup
    • (not MVP) doppler stretching
    • (not MVP) high quality pitch and time stretching using 3rd party libraries like Rubber Band Audio
    • (not MVP) support for long audio clips via disk streaming
  • Piano roll clip player node
    • A piano roll clip player node can house any number of clips
    • Clips can be assigned to multiple transports, as well as multiple places within the same transport
    • Clips can be played solo without a transport
    • Clips can be disabled
    • Supports CLAP note events and MIDI
    • Per-note expressions such as velocity, pan, timbre, pressure, etc.
    • Record into a new clip
    • (not MVP) custom tuning & microtonal scales
    • (not MVP) micro-pitch expressions
  • Automation clip player node
    • An automation clip player node can house any number of clips
    • Clips can be assigned to multiple transports, as well as multiple places within the same transport
    • Clips can be disabled
    • Arbitrary number of automation points
    • Linear, Bezier, and step
    • Record into a new clip
    • (not MVP) more advanced curves such as sine waves
    • (not MVP) sample-accurate automation
  • Recording node
    • Similar to the recorder in the audio clip player node, but can be placed anywhere in the graph. This allows you to do things like rendering a project to stems or bouncing a clip (pre or post FX).
  • Sample browser playback node (used to quickly play back a sample as the user clicks it in the browser)
  • (not MVP) Metronome node

General

  • Modular system that lets you choose what parts to include in your project
  • (not MVP) Good documentation and examples
  • (not MVP) C bindings

Non-Goals

  • No clip launcher (although it might be possible to do this with a custom node)
  • VST3 and LV2 support will not receive the same level of support as CLAP plugins
  • No support for the AUv2, AUv3, LADSPA, WAP (web audio plugin), or VCV Rack plugin formats
  • No time and pitch stretching on long audio files that are streamed from disk
  • Only exporting and recording audio to WAV will be supported
  • If I do decide to go with the MIT license, then certain modules will need to fall under a separate license such as VST3 hosting, ASIO, and Rubber Band Audio.

Tech Stack

Architecture

TODO