Chirp Analyzer

📖 Overview

By analyzing Blackbox logs containing swept-sine chirp setpoint signals, this tool calculates closed-loop frequency response: delivered rate (magnitude), latency (phase lag), tracking error, and motor saturation limits.

🛠️ How to Use

1. Fly Betaflight chirp mode (Betaflight 2025.12 or newer) to record a swept-sine setpoint on one axis at a steady throttle level.
2. Drag and drop your Blackbox .bbl log file into Slot A (or compare two logs using Slot A and Slot B).
3. Select the target axis (Roll, Pitch, or Yaw). Auto-detect automatically isolates the chirp excitation region.
4. Review the -3 dB Bandwidth cutoff and Worst-case Error metrics in the readout panel.

⚙️ Analysis Methods & Controls

• Welch H1 (Default): Classic cross-spectral estimate (Pxy/Pxx) with 50% overlapping windows. Window averaging produces smooth curves and enables the Coherence trust trace.
• Chirp Tracking: Slides an FFT window along the sweep to evaluate gyro/setpoint at the instantaneous chirp frequency. Ideal for short or custom chirp runs.
• Auto-Detection & Trimming: Auto-detect identifies the chirp frequency sweep signature automatically. Drag the highlighted band on the timeline to trim manually; switching axes re-runs auto-detection for that axis.
• Log F Toggle: Switches between logarithmic (2 Hz to 500 Hz) and linear frequency axes.
• Window (s): Sets FFT window length (0.5s default; 2.0s reaches sub-Hz frequencies).
• Show as % / Linear Axis: Converts magnitude/error dB curves into percentage of commanded stick amplitude.

📊 Understanding the Charts

• Magnitude / Delivered Rate: 0 dB (100%) indicates 1:1 tracking; the red line marks the -3 dB bandwidth limit (70.7% delivered rate).
• Latency: Equivalent millisecond delay (ms = phase / [360 × f]). Lower and flatter lines represent snappier response.
• Coherence: Measurement trust meter. Values near 1.0 indicate valid setpoint-driven gyro response; values below 0.6 indicate noise dominance (drawn dashed).
• Tracking Error: Rate not delivered (|setpoint - gyro|) in deg/s across the frequency sweep.
• Motor Saturation: Share of samples where any motor is pinned at max output (Sat High, default 98%) or idle floor (Sat Low, default 2%).

💡 Workflow & Privacy Tips

• Fly one sweep per axis per battery state, keeping throttle steady.
• Compare Log A vs Log B on the same axis with identical window settings to evaluate filter/PID tuning changes.
• All processing runs 100% locally in your browser — log files never leave your device.