PortaDSPKit · Swift · C++17 · Web Audio
++ Porta424 faithfully recreates the wow, flutter, saturation, head bump and hiss of a + vintage 4-track portastudio. Ship it in your app as a Swift package — or + play the real DSP right here, running live in your browser via the + Web Audio & Web MIDI APIs. +
+The same tape character DSP, ported to an AudioWorklet. Play the synth with
+ your computer keys, a MIDI controller, your mic, or a dropped audio file.
Computer keys A W S E D… play notes too.
+No audio? Browsers require a click before sound can start — hit POWER first. + The real Swift/C++ build runs the identical algorithms natively on iOS & macOS.
+Every imperfection that made cassette desirable, modeled in a real-time C++17 core.
Independent sine LFOs through a modulated fractional delay line, with slow random phase drift.
tanh soft-clip with calibrated drive and makeup gain for warm, musical compression.
Resonant low-frequency peak (~80 Hz, Q 1.4) recreating analog tape’s signature thump.
Gently colored additive noise, dialed in decibels-full-scale from silent to lo-fi.
Random, smoothed amplitude dips per minute — the sound of worn oxide.
Tunable low-pass roll-off from a bright 20 kHz down to a dusty 1 kHz.
Inter-channel bleed and timing jitter between tracks for true multitrack realism.
Noise-reduction encode/decode and parametric biquad EQ on every channel.
RMS level metering taps for VU displays, thread-safe from the audio thread.
Native nodes handle EQ & filtering; the custom tape physics live in an AudioWorklet — + the same split the native build uses between Swift and the C++ core.
Swift Package Manager. No Homebrew, CocoaPods, or Carthage.
// Package.swift
+dependencies: [
+ .package(url: "https://github.com/johnnyclem/Porta424.git", from: "1.0.0")
+]import AVFoundation
+import PortaDSPKit
+
+var params = PortaDSP.Params()
+params.satDriveDb = -2.0 // push saturation
+params.headBumpGainDb = 4.0 // warm low end
+params.hissLevelDbFS = -54.0 // audible hiss
+
+let porta = PortaDSP()
+porta.update(params)