DSPi turns a $4 RP2040/RP2350 Pico into a USB audio DSP processor with parametric EQ, active crossovers, room correction, and multi-channel I2S/S/PDIF output.
Key Takeaways
Plug-and-play USB audio class device (no drivers) on macOS, Windows, Linux, iOS; accepts 16/24-bit PCM at 44.1, 48, or 96 kHz.
RP2350 (Pico 2) gets 110 total EQ bands, hardware FPU, hybrid SVF/biquad filters, and up to 8 S/PDIF or I2S output channels plus PDM subwoofer.
RP2040 runs at 307.2 MHz (slight voltage bump to 1.15V) using hand-optimized ARM assembly for Q28 fixed-point math; RP2350 hits the same clock with hardware float.
Full signal chain: per-channel preamp, 10-band master EQ, RMS volume leveller with lookahead, BS2B headphone crossfeed with ITD, ISO 226:2003 loudness compensation, 2xN matrix mixer, per-output EQ, 85ms delay alignment, and master volume.
All GPIO pin assignments reconfigurable at runtime; firmware updates via USB vendor command without a physical BOOTSEL press.
Hacker News Comment Review
Commenters flag a key scope limit: the device is output-only and funnels a single stereo USB input pair through the DSP chain, ruling out multi-input mixing use cases.
The ASR forum thread (linked in comments) has more implementation detail and is where the creator is actively engaged with the audio community.
Notable Comments
@a96: flags output-only architecture and single USB stereo pair limit; links ASR thread where creator credits Claude Opus 4.5 as “my little robot intern” for busy work.
