ENGINE=radio · src/engine/radio/radio_engine.{h,cpp} · class RadioEngine
A dual virtual RadioMusic. Each deck (A/B) is an independent virtual radio browsing one shared SD library of banks; the two radios are blended by the platform crossfader and placed by the routing switch, so it plays like a pair of radios you tune and mix.
Its signature is the free-running virtual playhead: every station sounds as though it kept broadcasting while you were tuned elsewhere. A per-deck clock runs continuously; tuning to a station lands at the position it "would" be playing now, and leaving and returning finds it advanced - exactly like a radio.
Implementation, architecture, the file map, and the bug writeups live in >
docs/dev/radio-impl.md.
_Generated from docs/diagrams/controls/radio.json via make diagrams._
| Control | ParamId / config | Effect |
|---|---|---|
PITCH (Speed) | + V/oct CV jack | STATION select - the tuning dial. Knob + CV summed, quantized to the nearest station in the bank. |
POS (Pos) | + size/pos CV jack | START offset into the station (applied on the next switch / RESET). |
SIZE (Size) | varispeed 0.5x..2x (center = unity). RadioMusic is fixed-rate; this is a platform bonus. | |
ENV (Env) | inter-station STATIC amount (tuning hiss crossfaded in on a station change). | |
MIX (Mix) | deck volume. | |
Alt+PITCH (Aux) | BANK select (held selector, ring dots) - "hold RESET for bank" on the original. | |
Mix fader (Crossfade) | A/B blend of the two radios. | |
Routing switch (Route) | stereo topology (below). | |
| Play pad / gate-in | RESET - re-start a stopped deck at the live position (a no-op while it is already streaming). The Rev pad is inert. |
A filtered-noise "tuning hiss" crossfades in on each station change; ENV sets the level. With ENV high, sweeping PITCH switches stations immediately so you hear the dial-tuning churn + hiss; with ENV low, a sweep only opens the station you land on (no zipper). A non-playing deck (empty bank) outputs dead-air hiss at the ENV level.
Per deck the ring shows the station position (a bright marker at station/N) over a faint base, green while playing, amber on a failed open / empty bank. Holding Alt shows the BANK selector (16 dots, the current bank bright). The routing switch lights the mode L/C/R indicator.
You can download the original 8GB audio from the original radio music module from here. Place the files in the spotykach sd card as follows:
A shared library both decks browse independently:
/radio/0/ 01.raw 02.raw ... (bank 0)
/radio/1/ ... (bank 1)
...
/radio/15/ ... (bank 15, up to 48 stations each)0..15 (mirrors RadioMusic's 16 folders)..raw/.wav files in a bank. Use short 8.3 names (e.g. 01.raw); longer names are skipped..DS_Store and ._* companion files; the engine filters them, but to clean a card you can run dot_clean /Volumes/CARD and delete any remaining ._* / .DS_Store.Stations are signed 16-bit mono PCM, in either format (mix freely in a bank):
.raw - headerless (the original RadioMusic format). Carries no sample rate, so it assumes 48 kHz unless rate.txt overrides (below)..wav - a 16-bit-mono PCM WAV. Self-describing: it carries its own sample rate, so a 44.1k WAV plays at correct pitch with no rate.txt.The firmware does no sample conversion, so a non-16-bit / stereo / float file is rejected (.wav) or plays as garbage (.raw). Stations can be arbitrarily long (the originals run ~25 min / 130 MB each) - streaming has no length cap.
Convert sources with scripts/convert_radio_audio.py. The original RadioMusic library is itself headerless 16-bit-mono .raw at 44.1 kHz, so the converter resamples it to 48 kHz; --format wav writes self-describing WAV stations instead. The whole-card mirror command reproduces a stock card under /radio, preserving names:
# mirror a RadioMusic card's 0..15 folders into /radio/0..15 at 48 kHz, keeping names
scripts/convert_radio_audio.py mirror --keep-names -o /Volumes/SD ~/Downloads/16gb-Disk
# ...as self-describing WAV (no rate.txt needed)
scripts/convert_radio_audio.py mirror --format wav --keep-names -o /Volumes/SD ~/Downloads/16gb-Disk
# one bank from a folder of your own files
scripts/convert_radio_audio.py from-dir --bank 0 -o /Volumes/SD ./samples
# or a one-liner per file
ffmpeg -i in.wav -ac 1 -ar 48000 -f s16le /Volumes/SD/radio/0/01.rawrate.txt, .raw only)A headerless .raw carries no sample rate, so the engine assumes 48 kHz. To play an unconverted original card (44.1 kHz) at correct pitch without converting, drop a one-line text file /radio/rate.txt with the source rate:
44100Any rate in 8000..192000 is accepted (RadioMusic's 11025/22050/44100/48000/96000 all work). It rebases playback so SIZE-at-noon gives correct pitch. rate.txt applies to .raw only - a .wav carries its own rate. Without conversion or rate.txt, an original 44.1 kHz card plays ~9% sharp (also pullable by ear with SIZE).
So three ways to play an original 44.1 kHz library at correct pitch: convert to 48 kHz .raw with mirror, convert to .wav (--format wav, no rate.txt), or drop the .raw files in as-is and add rate.txt.
make -j8 ENGINE=radio # build (~83% SRAM_EXEC)
make engine-radio # clean + build + DFU flash
make -C host test # host suites incl. test-radio