I have made a major change in the DSP direction of Darśana.

In my measurement bench, I found a new way to compensate for the discretization errors of a forward-Euler ladder filter; especially cutoff tuning and resonance behavior near the high-frequency range.

With this correction, the forward-Euler ladder now performs at a level comparable to, and in some cases better than, my previous TPT/bilinear ZDF ladder implementation in my measurement bench.

The important result is simple:

I can now get a more analog-like sound from a much lighter ladder structure.

This changes the design trade-off significantly. Instead of spending most of the CPU budget on a heavy zero-delay feedback ladder, I can use a corrected forward-Euler ladder core, run the nonlinear filter section at 4× oversampling; 192 kHz internally; and still have room for more musical features.

Core 0 is fully dedicated to the main synth engine:

• 5-voice polyphony
• 3 oscillators + noise per voice
• corrected nonlinear 4-stage ladder filter
• 4× oversampled filter processing

At the same time, I have started using Core 1 for built-in stereo effects. The current firmware now includes chorus and delay running alongside the main synth engine.

The result is a richer, wider, and more analog-like sound than before, while still running on the Raspberry Pi Pico 2 / RP2350.

Please listen to how far this little microcontroller can be pushed.