Dopplerize

🌊 Why Does Pitch Bend When Things Move? (The Doppler Deep Dive)

The Doppler effect isn't magic — it's geometry + wave physics. When a sound source moves toward you, each wave crest gets emitted from a slightly closer position. The waves compress → higher frequency → higher pitch. When it recedes, waves stretch → lower pitch.

The formula (no panic):


            f_observed = f_source × c / (c ∓ v_radial)

c = speed of sound (343 m/s) • v_radial = how fast the source moves toward/away from you

🎛️ Your Controls, Decoded

🚗 Vehicle speed (mph): Faster car = bigger pitch swing. At 300 mph, the shift is dramatic (~±20%). At 10 mph, it's subtle. Try: 65 mph + 5 ft distance for that classic "NASCAR flyby" sound.
📏 Road distance (ft): This is your orthogonal distance — how far you stand from the road's edge. Close (5 ft) = sudden "WHEEE-oooom" pitch drop. Far (200 ft) = gentle, sweeping glide. Physics reason: radial velocity changes fastest when you're near the path.
🔊 Volume: Real sound obeys the inverse-distance law: double the distance = quarter the intensity. We normalize this so "100%" = loudest at closest approach. Crank to 300–500% for headphone-friendly "car stereo" levels.
🎚️ Manual pitch bend (cents): Override physics! 100 cents = 1 semitone. Bend +1200 = shift up an octave. Pro use: Compensate for recording pitch, or create alien vehicle sounds.
⏱️ Simulation speed: Time dilation for your ears. 0.5× = slow-mo analysis. 3× = quick demo. Doesn't change physics — just how fast the car "drives" through the 10-second window.
❄️ Freeze at closest point: Lock the pitch shift at the moment of closest approach. Why? Sustain that "peak Doppler" tone for analysis, or create a static shifted loop.
⇄ Reverse direction: Flip the car's travel direction. Physics is symmetric, but perception isn't — approaching high pitch → receding low pitch feels different than the reverse.

🌌 Doppler in the Wild

🚑 Ambulances: That iconic "nee-naw" is Doppler + siren modulation. The pitch drop at closest approach is ~15–25% for typical speeds.
🏎️ F1 cars: At 200 mph, the shift is ~±30%. Combined with engine harmonics, it creates that visceral "scream-then-growl" effect.
🔭 Astronomy: Redshift/blueshift of starlight uses the exact same math — but with light speed (c = 300,000 km/s). Hubble measured universe expansion this way.
🦇 Bats & dolphins: They emit calls and listen for Doppler-shifted echoes to calculate prey velocity. Nature's radar.

🧪 Try This Experiment:

Set Speed=65 mph, Distance=10 ft, Volume=300%
Click Play, then slowly drag Distance from 10 → 200 ft
Listen: the pitch transition changes from "sudden drop" to "smooth glide"
Why? Radial velocity derivative dv_radial/dt is largest at small distances

💡 Fun fact: Christian Doppler predicted this effect in 1842 using light from binary stars. It took 3 years for someone to test it with trumpeters on a moving train. Science: sometimes you need brass + rails.

🚗 Dopplerize

What is Dopplerize?

🌊 Why Does Pitch Bend When Things Move? (The Doppler Deep Dive)

🎛️ Your Controls, Decoded

🌌 Doppler in the Wild