OS-251 Is a FREE Lo-Fi Synthesizer Plugin by Onsen Audio

OS-251 FREE Lo-Fi Synthesizer Plugin by Onsen Audio

Onsen Audio has announced the release of OS-251, a free Lo-Fi synthesizer plugin for macOS, Windows and Linux.

They say:

OS-251 is a “JUNO” style digital subtractive synthesizer with a simple yet powerful DSP algorithm. Unlike other plugins that use analogue simulation, OS-251 uses digital algorithms to give warm, lo-fi sounds. The design of the oscillators and the selection of parameters were influenced by the JUNO-106, making it easier to express a thicker, chunkier sound.

The oscillator has alias noise (specific to digital signal processing) famous on classic samplers like E-mu SP-12 which adds lo-fi feeling to the sound. You can enjoy the powerful sound at modern sampling rates with your DAW.


  • Up to 10 voices of polyphony
  • Oscillators (Sin, Square, Saw), with Shape parameter
  • Square sub-oscillator
  • Noise oscillator
  • Biquad low-pass filter (LPF) with Frequency and Resonance parameters
  • Biquad high-pass filter (HPF) with Frequency parameter
  • Envelope generator which can control LPF and amplitude
  • Low-frequency oscillator (LFO) which can control LPF, amplitude, and Shape parameter
  • LFO sync
  • Chorus
  • Flexible pitch controls (pitch bend width, octave, semitone, fine-tuning)

OS-251 is available in VST3 and AU plugin formats.

More information: Onsen Audio

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