Echoscope — Browser Sonar

Linear FM sweep — transmits a sinusoidal tone that sweeps from frequency f1 up to f2 over duration T. Cross-correlation with the reference produces a sharp peak at each echo delay.

Best for: quick single-ping measurements, short-range detection, and real-time interactive use. Lowest latency of all modes (single short burst). Good default for getting started.

Trade-offs: moderate sidelobe level in the correlation (can show ghost peaks near strong echoes). SNR scales with bandwidth (f2 − f1) and duration T. Narrower bandwidth = worse range resolution.

Settings:

• f1 — start frequency (Hz). Lower values penetrate obstacles better but may be audible. Default 2000 Hz.
• f2 — end frequency (Hz). Higher values give finer range resolution. Default 9000 Hz. Bandwidth = f2 − f1.
• T — chirp duration (ms). Longer = higher SNR but slower ping cycle. Default 7 ms.

Maximum Length Sequence — transmits a pseudo-random binary sequence (PRBS) generated by a linear-feedback shift register (LFSR). Each chip is held for 1/chipRate seconds, producing a wideband noise-like signal. The circular auto-correlation of an MLS is a near-perfect impulse (flat sidelobes at −1/L).

Best for: high-SNR room impulse response measurements. Excellent for scanning and heatmap generation where you need reliable echo detection across the full range. Good noise rejection thanks to the spread-spectrum nature of the signal.

Trade-offs: longer signal than chirp (higher latency per ping). Single-ping only (no sidelobe cancellation like Golay). Sensitive to Doppler shift from fast-moving targets (correlation peak broadens).

Settings:

• Order (m) — LFSR register size. Sequence length = 2^m − 1 chips. Higher m = longer signal = better SNR but more compute and latency. Range 2–16, default 12 (4095 chips).
• Chip rate — chips per second (Hz). Higher = wider bandwidth = finer range resolution, but requires higher sample rate headroom. Default 4000 Hz.

Complementary Golay sequences — transmits two binary sequences (A then B) separated by a short gap. Their individual auto-correlations have sidelobes of opposite sign, so summing corr(A) + corr(B) produces a perfect impulse with zero sidelobes. This is the cleanest impulse response achievable.

Best for: calibration, high-accuracy scanning, and environments with strong multipath. The zero-sidelobe property eliminates ghost peaks, giving the most reliable range and angle estimates. Recommended for laptop preset scan mode and whenever measurement quality matters most.

Trade-offs: requires two transmissions per ping (A + gap + B), so each measurement takes roughly 2× longer than chirp or MLS. The sidelobe cancellation assumes the scene is static between A and B; fast-moving targets may degrade cancellation.

Settings:

• Order (n) — sequence length = 2^n chips per half (A and B each). Higher n = longer signal = better SNR. Range 1–14, default 10 (1024 chips).
• Chip rate — chips per second (Hz). Controls bandwidth and range resolution, same as MLS. Default 5000 Hz.
• Gap A→B — pause between transmitting A and B (ms). Must be long enough for reverb from A to decay before B starts, but short enough to assume static scene. Default 12 ms.

Frequency-division probing — transmits several orthogonal tones in one symbol and demultiplexes them with FFT/correlation. This reduces sweep time by evaluating multiple spectral channels in parallel.

Best for: faster scan loops and adaptive per-device carrier masking after calibration.

Trade-offs: requires careful carrier spacing and quality weighting to avoid leakage and noisy subcarriers.