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kai-rem
Jan 12, 2026


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.

cargo run --release -- --poly 8 --mode supersaw --midi virtual

And yes, you can play notes with the keyboard when you do not have MIDI.