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Pink noise as a source (mode "pink")

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Core: aes67_tx_pink_noise(), a ready-made TX source: xorshift32 white noise
through Paul Kellet's pink filter, -18 dBFS RMS (peaks about -6 dBFS), same
on L and R. The player uses it like the tone (straight to TX, no volume or
gain). Checked on the board: -18 dBFS RMS, octave bands 63 Hz-4 kHz flat
within +-0.4 dB, L = R.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
This commit is contained in:
Ben Nicholson
2026-09-25 23:37:05 +10:00
parent bbeb7d3fd2
commit 122e46e862
8 changed files with 58 additions and 16 deletions
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docs/hardware-and-design-notes.md
+3 -3
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@@ -18,7 +18,7 @@ Core AES67 parts (PTP, TX, SDP/SAP, network/VLAN, syslog, web UI base, config sc
## Project pipeline
source (cspot Spotify Connect | HLS player) -> decode (Vorbis/AAC/MP3) -> SRC 44.1k->48k -> PSRAM ring buffer -> volume/gain -> aes67_tx pull callback
- Volume is applied after the ring (in the pull callback) so a change is heard at once, not one ring length (4 s) later; ramped over one packet to avoid zipper noise. Curve: amplitude = (volume/100)^3 (about -18 dB at 50 %, 0 = mute). The built-in test tone (mode "tone") is not affected.
- Volume is applied after the ring (in the pull callback) so a change is heard at once, not one ring length (4 s) later; ramped over one packet to avoid zipper noise. Curve: amplitude = (volume/100)^3 (about -18 dB at 50 %, 0 = mute). The built-in test signals (modes "tone", "pink") are not affected.
- Spotify Connect: cspot (feelfreelinux/cspot), needs Premium, zeroconf via mDNS (on the internet interface when VLAN split). Spotify occasionally changes auth for 3rd-party clients — expect breakage risk.
- HLS: HTTPS (mbedTLS), m3u8 parse (master->media playlist), segment fetch, TS demux or fMP4/ADTS, AAC decode (esp_audio_codec / esp-gmf).
- Stereo L24/48k at 1 ms is about 3 Mbit/s on the wire; 100 Mb has plenty of headroom.
@@ -31,10 +31,10 @@ source (cspot Spotify Connect | HLS player) -> decode (Vorbis/AAC/MP3) -> SRC 44
- Firmware needs Spotify events: cspot connect, disconnect, play, pause.
## Project config group
- source: {mode: spotify|hls|auto|tone|off, spotify_name, spotify_bitrate, hls_url, autoplay, gain_db, failover_delay_s, failover_on_pause, spotify_client_id, spotify_client_secret}
- source: {mode: spotify|hls|auto|tone|pink|off, spotify_name, spotify_bitrate, hls_url, autoplay, gain_db, failover_delay_s, failover_on_pause, spotify_client_id, spotify_client_secret}
- spotify_client_id / spotify_client_secret: each user's own Spotify developer app (developer.spotify.com, Premium account), needed by the maintained cspot fork (philippe44/cspot) since Spotify's 2025 API restrictions. The secret is write-only (never returned by GET /api/config). spotify_state reports "no client credentials" while either is missing.
- Project status fields: active_source, source_state, spotify_state, buffer_ms
- mode "tone": the core's 1 kHz / -18 dBFS test tone, phase-locked to PTP (commissioning, e.g. Riedel import tests). "off": silence.
- mode "tone": the core's 1 kHz / -18 dBFS test tone, phase-locked to PTP (commissioning, e.g. Riedel import tests). "pink": the core's pink noise, -18 dBFS RMS (peaks about -6 dBFS), same on L and R (level/EQ checks). Neither is affected by volume or gain. "off": silence.
## Player control API (project routes)
- GET /api/player -> {source, forced, state(playing|paused|stopped|buffering|idle), artist, title, album, position_ms, duration_ms, volume(0-100), can:{pause,next,prev,seek}}