Octasine is a free, open-source frequency modulation (FM) synthesizer. Open source means its code is public, so anyone can inspect it, and it is developed as a community-friendly project. Before installing, check the project's official page for the latest release, supported plugin formats and operating systems, since these can change between versions.
What is FM synthesis?
In FM synthesis, one oscillator (the modulator) changes the frequency of another (the carrier) at audio speed. The result is complex, harmonically rich tones that subtractive synths struggle to create: bells, electric pianos, metallic basses and glassy pads.
| Term | Meaning |
|---|---|
| Operator | An oscillator that can act as a carrier or modulator |
| Carrier | The operator you hear |
| Modulator | The operator that shapes the carrier's frequency |
| Ratio | The frequency relationship between operators |
| Feedback | An operator modulating itself for brighter, noisier tones |
Why try Octasine
- Free and open: no cost and public source code.
- Compact interface: learning FM is easier when the layout is clear.
- Good for sound design: it is a great way to learn how FM works.
- Community support: open projects usually have issue trackers and documentation.
Installing safely
- Visit the project's official page (usually a code hosting page) and pick the release for your operating system.
- Read the notes to see which plugin formats are included and how to install them.
- Copy the plugin to your DAW's plugin folder as instructed.
- Rescan plugins and load Octasine on an instrument track.
Only download from the official project page. Open-source software is safe when it comes from the source, and risky when it comes from random mirrors.
Making your first sounds
Electric piano
Use a carrier with a sine wave and a modulator at a 1:1 or 14:1 ratio at a low level. Give the modulator a short decay so the attack is bright and then mellows, like a struck tine.
Bell
Use a non-integer ratio such as 3.5 between modulator and carrier, with a long decay on both. Non-integer ratios create inharmonic overtones that resemble bells.
Bass
Set a low carrier with a 1:1 modulator and a fast envelope on the modulation amount. Add a little feedback for growl.
Tips for learning FM
- Change one parameter at a time and listen.
- Keep modulation levels low at first, as high levels turn tones into noise.
- Use integer ratios for pitched sounds and non-integer for bells and metal.
- Save patches you like with descriptive names.
Mixing FM sounds
FM sounds can be bright and full of high harmonics. A gentle low-pass, some saturation and a reverb from a free plugin like Valhalla Supermassive make them sit better. Keep an eye on peaks with the help of our gain staging guide.
More free instruments
For other free synths and effects, browse the free VST plugin collection.
Key takeaways
- FM synthesis uses operators to modulate each other's frequency.
- Integer ratios give harmonic tones; non-integer ratios give bells.
- Download from the official project page and check formats.
- Start with low modulation levels.
Modulating over time
FM sounds come alive when the modulation amount changes during a note. Assign an envelope to control how strongly a modulator affects the carrier. A quick decay creates a bright pluck; a slow attack creates a swelling, evolving pad. Using an LFO on the modulation level adds slow movement that keeps sustained notes interesting.
Getting involved
- Read the documentation and release notes on the project page.
- Report bugs clearly with your operating system and DAW version.
- Share patches or tutorials if the project welcomes community contributions.
- Respect the licence when you redistribute anything.
Open-source tools improve through user feedback, so a well-written bug report is a genuine contribution.
Preparing sounds for a mix
After designing a patch, bounce it to audio and edit the result. Trim silence, fade the ends and normalise if needed. Working with audio is faster on the CPU and frees you to focus on arrangement.
FAQ
Is Octasine really free?
It is presented as free and open source. Check the project's page for its licence and latest version.
Is FM synthesis hard to learn?
It can feel unusual at first, but working with a few operators and small changes makes it manageable.
Which formats and platforms does it support?
This varies by release, so read the official page before you download.
Can I use Octasine sounds commercially?
The sounds you create are generally yours, but read the project's licence for confirmation.
Get OctaSine (free, open source)
