Urban Birdsong vs. Traffic Noise

Street Conditions

Traffic noise level 65 dB

Song minimum frequency 3.0 kHz

Listener (mate) distance 40 m

Live Readouts

Song detected at listener —

Active space radius

— m

Detection margin

— dB

Noise at song freq.

— dB

Air absorption

— dB/m

How it works

Traffic noise is loudest at low frequency and fades at high frequency; air absorption does the opposite — it eats high frequencies fastest. A bird's song can only be heard where it beats both:

Received level:  L(r) = L0 − 20·log10(r) − α(f)·r
Traffic masking: N(f) = Ltraffic − 20·log10(1 + f/0.4)
Detected when:   L(r) − N(f) ≥ SNR_min  (6 dB)
α(f) ≈ 0.02·f^1.7   dB per metre (f in kHz)

Traffic noise level — ambient roadway sound (dB at the source); low-frequency-heavy, exactly like real engine/tire noise.
Song minimum frequency — the pitch the bird sings at. Traffic masks low pitches hardest, but air absorbs high pitches fastest over distance — there is a real optimum in between.
Listener distance — how far the mate or rival stands; the pill turns red once that distance exceeds the song's active-space radius.
Auto-adapt — scans frequencies and jumps to the one that maximises active space at the current noise level, mimicking the frequency-raising documented in real urban songbirds (e.g. great tits, European robins) living beside busy roads.

Active-space radius is solved by bisection on L(r) − N(f) = SNR_min. Raise traffic noise and, without adapting, the radius collapses — sing higher and it partially recovers, at the cost of faster atmospheric loss over long range.

Active space Singing bird Traffic

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