Sonifying the Multi-Probe Sky

How the sonification works. Multipole ℓ maps to audio frequency via log-log scaling (ℓ=2 → 40 Hz, ℓ=6000 → 8 kHz). The CMB first acoustic peak at ℓ∼220 lands near middle C (~270 Hz), the tSZ peak (ℓ∼2000) at ~2.7 kHz, and the CIB peak (ℓ∼5000) at ~6.8 kHz. Amplitude is globally normalized so variations in D_ℓ are preserved during sweeps (otherwise per-buffer normalization would flatten the dynamic range).

Synthesis methods. Shaped Noise filters white noise so its spectrum matches D_ℓ — the most faithful representation, sounds textural. Additive sums sine tones weighted by √D_ℓ — more tonal, individual peaks audible as distinct pitches. Scale Layers splits the spectrum into a bass drone (ℓ<100), harmonic tones at the CMB acoustic peaks (ℓ=220, 540, 810), and high-ℓ bandpass noise — makes the scale structure explicit as three different timbres. Instruments plays the spectrum as continuous gliding voices: each component gets its own instrument (piano/violin/guitar/flute/bass/synth, assignable via dropdown or palette preset). The octave is set by ℓ, the note name by observing frequency (93 GHz = A, 143 GHz = C#, 353 GHz = E), and the volume by √⟨D_ℓ⟩ integrated over an octave-wide band around the current ℓ, not just the single point. Each instrument has its own articulation rhythm (piano: re-strikes with per-harmonic decay rates; violin: bowed swells with vibrato; guitar: distorted strums; etc.). All instruments have convolution reverb.

3D Spatial mode places each component at a fixed position around the listener (CMB ahead, tSZ left, CIB right) using HRTF panning. Sphere clicks become localized drum hits at the actual sky position. Use headphones for the effect.

🌟 Big Bang button plays a 12-second standalone sonification based on Cramer (2003)'s scaling of the actual CMB acoustic peaks at ℓ=220, 540, 810, 1120, 1400, 1750, 2150, 2600 to audible frequencies, with their relative D_ℓ amplitudes. The pitch slowly descends to evoke the cosmic expansion.

Sweep modes. ℓ-Sweep moves a bandpass window across multipole in time; drag the Sweep position slider to scrub manually. Sweep options: log volume (dB-scaled amplitude for a wider dynamic range), linear ν-sweep (linear in ℓ instead of log, spends more time at high ℓ), ping-pong (bounce back and forth), and fixed pitch (keep audio pitch at 440 Hz while the input ℓ varies — isolates amplitude/timbre variation from the confounding pitch change). Build-Up progressively adds CMB → tSZ → CIB so you hear the components layer up into T_tot. ν-Sweep crossfades 93 → 143 → 353 GHz so you hear the foreground transition from CMB-dominated to CIB-dominated. During any sweep the plot shows a cursor, the current ℓ value, the total D_ℓ, and amplitude markers on each active component curve.

Stereo modes (headphones recommended): Components L/R splits active components into the two ears, so you can directly A/B compare (e.g. CMB left, tSZ right). 93|353 GHz places 93 GHz in the left ear (CMB-dominated) and 353 GHz in the right (CIB-dominated) — the clearest way to hear the foreground transition.

Interactive 3D sphere. The sphere shows the actual sky map at the selected component & frequency. Drag to rotate. Click any location to sonify it: (1) a drum hit plays whose fundamental frequency encodes the temperature at that pixel (cold → low, hot → high); (2) the continuous texture's amplitude is modulated by the local RMS fluctuation in the surrounding patch; (3) any nearby halos (orange dots are the 3000 most massive clusters with M>5×10¹⁴ M_⊙) fire a ping whose pitch encodes halo mass (heavier = higher). Toggle Scan mode to fire all three continuously while dragging, turning your cursor into an ear moving across the sky. The tSZ map in particular is cluster-dominated — in scan mode it sounds like a field of discrete chirps against a quiet background.