kai-rem
Lately I have been working on kai-rem, a realtime synth engine with a minimalist UI. The goal this week: add more sound engines, bolt on per-channel FX, and keep the interface simple enough to play without a manual.
Below is a quick, casual tour of what I changed, what worked, and a few gotchas I tripped over.
The short version
- Added four engines: Supersaw, Ring Mod, Pluck (Karplus), Formant.
- Added per-channel FX modules: Drive, Delay, Chorus, Crush.
- Kept the UI compact: each channel gets a dropdown + amount slider.
- Routed keyboard input to the selected channel for easy auditioning.
The original synth had the basics (subtractive, wavetable, FM, pulse, noise). Great for testing, but I wanted more contrast:
- Supersaw for that classic wide, buzzy pad.
- Ring Mod for metallic and alien textures.
- Pluck/Karplus for instant “stringy” sounds.
- Formant to get vowel-ish timbres without a full filter bank.
The nice part about these is that they share a lot of code. Once the oscillator and filter plumbing is in place, new engines are mostly different signal paths.
Per-channel FX
I went with a single FX slot per channel:
- None
- Drive (tanh saturation)
- Delay (simple feedback delay)
- Chorus (modulated delay line)
- Crush (bit + sample rate reduction)
UI tweaks: small but important
The channel rack now shows:
- Track select, mute, solo
- Pan slider
- FX dropdown
- FX amount slider
I nudged the left column width to make room. The big UX improvement was simple: keyboard notes now go to the selected channel, not just channel 1. That makes testing per-channel FX feel immediate.
Implementation notes
A few things worth mentioning:
- Audio thread is sacred. All UI updates go through a ring buffer to avoid blocking.
- FX are in the mixer, not in the voice. This keeps engines clean and lets FX act on the mixed channel signal.
- Formant uses bandpass filters. I added a bandpass output to the SVF for this.
- Karplus gets a tiny delay buffer per voice. Cheap, cheerful, and good enough for the vibe.
And yes, you can play notes with the keyboard when you do not have MIDI.