observer effect content

services/observer-effect/site/sfx/generate.sh

@@ -0,0 +1,65 @@
+#!/usr/bin/env bash
+# Synthesize the Observer Effect SFX with ffmpeg. Pure lavfi synthesis — no
+# samples. Re-run to regenerate the .mp3s in this directory.
+#
+#   nix-shell -p ffmpeg --run ./generate.sh
+#
+# Expressions are deliberately comma-free (logistic gates 1/(1+exp(-k*(t-T)))
+# and exp() envelopes instead of between()/min()/max()) so nothing needs
+# escaping inside the filtergraph.
+set -euo pipefail
+cd "$(dirname "$0")"
+
+SR=48000
+MP3=(-ac 1 -c:a libmp3lame -b:a 128k)
+# Per-second clicks use WAV: mp3 adds a few ms of priming silence at the buffer
+# start, which smears the transient against the digit changeover.
+WAV=(-ac 1 -c:a pcm_s16le)
+
+# --- pulse: a deep drum thump, a rising flute whistle, a metallic shimmer ----
+PULSE='exp(-5*t)*0.9*sin(2*PI*(90*t-25*t*t))'
+PULSE+=' + (1-exp(-25*t))*exp(-3*t)*0.16*sin(2*PI*(1500*t+850*t*t))'
+PULSE+=' + exp(-2.2*t)*0.05*sin(2*PI*2700*t)*(1+0.5*sin(2*PI*7*t))'
+ffmpeg -y -hide_banner -loglevel error \
+  -f lavfi -i "aevalsrc=${PULSE}:s=${SR}:d=1.4" \
+  -af "aecho=0.8:0.7:45|110:0.35|0.2,alimiter=limit=0.95,aresample=44100" \
+  "${MP3[@]}" pulse.mp3
+
+# --- communion: rising roar + noise swell -> sub-bass impact -> screaming
+#     flutes over a beating void drone -------------------------------------
+ROAR='(1-exp(-2.5*t))*exp(-0.28*t)*0.28*(sin(2*PI*(60*t-2.5*t*t))+0.5*sin(4*PI*(60*t-2.5*t*t))+0.33*sin(6*PI*(60*t-2.5*t*t)))'
+IMPACT='(1/(1+exp(-30*(t-1.6))))*exp(-3.2*(t-1.6))*0.95*sin(2*PI*(80*(t-1.6)-35*(t-1.6)*(t-1.6)))'
+FLUTES='(1/(1+exp(-30*(t-1.7))))*exp(-0.9*(t-1.7))*0.07*(sin(2*PI*1700*t)+sin(2*PI*2050*t)+sin(2*PI*2390*t)+sin(2*PI*2900*t)+sin(2*PI*3550*t))*(1+0.4*sin(2*PI*5*t))'
+DRONE='(1/(1+exp(-25*(t-1.7))))*exp(-0.5*(t-1.7))*0.22*(sin(2*PI*40*t)+sin(2*PI*40.5*t))'
+TONAL="${ROAR} + ${IMPACT} + ${FLUTES} + ${DRONE}"
+SWELL="volume=volume='0.4*(1-exp(-2.2*t))*(1/(1+exp(8*(t-1.95))))*(0.6+0.4*sin(2*PI*0.9*t))':eval=frame"
+ffmpeg -y -hide_banner -loglevel error \
+  -f lavfi -i "aevalsrc=${TONAL}:s=${SR}:d=6.5" \
+  -f lavfi -i "anoisesrc=color=white:amplitude=0.6:r=${SR}:d=6.5" \
+  -filter_complex "[1:a]highpass=f=3000,${SWELL}[n];[0:a][n]amix=inputs=2:normalize=0,aecho=0.8:0.85:55|150:0.35|0.2,alimiter=limit=0.96,aresample=44100[out]" \
+  -map "[out]" "${MP3[@]}" communion.mp3
+
+# --- whisper: a brief eerie transmission for broadcast text ------------------
+WHISP='(1-exp(-8*t))*exp(-2*t)*0.12*(sin(2*PI*620*t)+sin(2*PI*623*t))'
+WHISP+=' + exp(-3*t)*0.04*sin(2*PI*(2200*t-300*t*t))'
+WHISP+=' + 0.03*exp(-1.5*t)*sin(2*PI*1240*t)*(1+0.6*sin(2*PI*11*t))'
+ffmpeg -y -hide_banner -loglevel error \
+  -f lavfi -i "aevalsrc=${WHISP}:s=${SR}:d=1.6" \
+  -f lavfi -i "anoisesrc=color=white:amplitude=0.25:r=${SR}:d=1.6" \
+  -filter_complex "[1:a]bandpass=f=1500:width_type=h:w=900,volume=volume='0.18*exp(-2.5*t)*(0.5+0.5*sin(2*PI*13*t))':eval=frame[n];[0:a][n]amix=inputs=2:normalize=0,volume=12dB,aecho=0.8:0.6:70:0.3,alimiter=limit=0.9,aresample=44100[out]" \
+  -map "[out]" "${MP3[@]}" whisper.mp3
+
+# --- relay: a dry electromechanical seconds step (armature snap + body) -------
+#   The seconds advance is a stepping relay, not a pendulum: a sharp broadband
+#   snap with a faint low "thunk" and almost no tonal tail.
+RELAY='exp(-120*t)*0.3*sin(2*PI*430*t) + exp(-220*t)*0.32*sin(2*PI*1700*t)'
+ffmpeg -y -hide_banner -loglevel error \
+  -f lavfi -i "aevalsrc=${RELAY}:s=${SR}:d=0.09" \
+  -f lavfi -i "anoisesrc=color=white:amplitude=0.6:r=${SR}:d=0.09" \
+  -filter_complex "[1:a]bandpass=f=2400:width_type=h:w=2400,volume=volume='0.6*exp(-230*t)':eval=frame[n];[0:a][n]amix=inputs=2:normalize=0,alimiter=limit=0.95,aresample=44100[out]" \
+  -map "[out]" "${WAV[@]}" relay.wav
+
+echo "generated:"
+for f in pulse.mp3 communion.mp3 whisper.mp3 relay.wav; do
+  printf '  %-14s %s\n' "$f" "$(du -h "$f" | cut -f1)"
+done