The notch filter is Betaflight’s sharpest tool against motor noise — but it’s also the easiest to misconfigure. Set it too wide and you lose propwash handling. Set it too narrow and motor noise bleeds through. I’ve spent dozens of hours staring at blackbox spectrograms and the lesson is clear: notch filter config is a strategy, not a setting. Here’s the strategy that works.
Understanding the Notch Filter Architecture
Betaflight applies up to four notch filters in series to the gyro signal before it reaches the PID controller: two dynamic notches (D-term and gyro) and two fixed notches (static band-reject filters). Each removes a specific frequency band from gyro data.
Dynamic notch: Tracks the motor RPM in real time. As you throttle up, it follows the motor’s fundamental frequency and its harmonics. This is the “smart” filter — it only cuts where noise actually exists, and it moves with motor speed.
Fixed notch: A static band-reject filter at a constant center frequency. It’s a “dumb” filter — always cutting the same frequency regardless of motor speed. It’s useful on builds with a known resonance (frame ringing, camera vibration) but harmful when it overlaps with flight dynamics frequencies.
The key insight: every Hz of filtering you add is a Hz of flight information you lose. Over-filtering feels like flying through mud — sluggish, deadened, unresponsive. Under-filtering shows up as oscillations.
Step 1: Run a Blackbox Log Before Touching Any Filter
Connect with props on, fly a test pack that includes: hover (5 seconds), punch-out to full throttle (2 seconds), mid-throttle cruise (10 seconds), and aggressive snap rolls and flips. Land, download the blackbox log, and open it in Plasmatree or Betaflight Blackbox Explorer.
Look at the gyro spectrogram. You’ll see horizontal lines at the motor’s RPM frequency (and its harmonics) — these are your motor noise bands. The fundamental is typically 200-400Hz at hover, rising to 600-800Hz at full throttle. The 2nd harmonic (doubled frequency) is often the most problematic because it falls right where frame resonances live.
Count the noise bands. If you see 1-2 strong bands, dynamic notch alone can handle it. If you see 3+ bands or noise that doesn’t move with RPM, you need fixed notches too — but only where the spectrogram shows real energy.
Step 2: Configure the Dynamic Notch First
The dynamic notch has three critical parameters:
Dynamic Notch Range: The frequency window where the dynamic notch is allowed to operate. Default is MEDIUM (80-330Hz for gyro, 175-500Hz for D-term). If your motor noise fundamental is outside this range at any throttle position, widen it.
Dynamic Notch Q: Controls how wide each notch is. Lower Q = wider cut = more filtering but more phase delay. Higher Q = narrower cut = less filtering but preserved flight feel. Start at the default (Q=120 for gyro, Q=250 for D-term) and only adjust if blackbox shows residual noise after tuning.
Dynamic Notch Min/Max Hz: Hard limits on where the dynamic notch can move. If your motor’s fundamental never goes above 500Hz, set max to 500 — letting the filter wander higher just cuts into flight response for no benefit.
Verification: After setting dynamic notch, fly and log again. The motor harmonics in the new spectrogram should be significantly attenuated. If they’re still visible at hover or punch-out, adjust Q factor downward (wider) in 20-unit increments until they disappear.
Step 3: Add Fixed Notches Only Where Needed
Fixed notches are your last resort. Each one adds group delay — the time it takes for the filter to process the signal. Too much group delay and the quad feels disconnected from your stick inputs.
Only add a fixed notch when:
– The spectrogram shows a noise band at a fixed frequency (doesn’t move with RPM) — this is a frame resonance or camera vibration
– The noise amplitude at that frequency is high enough to cause visible oscillations in flight
– You’ve already optimized dynamic notch and RPM filtering and the noise persists
When adding a fixed notch, set the center frequency to the exact noise peak and the cutoff to as narrow as possible (high Q) — you’re surgically removing one specific resonance, not a whole band.
Gyro Notch Filter Parameter Reference
| Parameter | Default | Conservative | Aggressive | Effect of Going Too Far |
|---|---|---|---|---|
| Gyro Dynamic Notch Range | MEDIUM (80-330Hz) | LOW (100-270Hz) | HIGH (60-400Hz) | Too wide: filter chases phantom noise, adds latency |
| Gyro Dynamic Notch Q | 120 | 80 (wider) | 200 (narrower) | Too low: dull flight feel, poor propwash handling |
| D-term Dynamic Notch Range | MEDIUM (175-500Hz) | LOW (200-400Hz) | HIGH (120-600Hz) | Too wide: D-term gets mushy, loss of sharpness |
| D-term Dynamic Notch Q | 250 | 150 (wider) | 350 (narrower) | Too low: D-term phase delay increases, bounce-backs |
| Fixed Notch Count | 2 | 0 | 4 | Each adds 0.2-0.5ms group delay — cumulative |
| Gyro RPM Filter Harmonics | 3 | 1 | 5 | Filtering harmonics that don’t exist = wasted CPU |
Common Mistakes in Notch Filter Configuration
Mistake 1: Enabling all filters “just to be safe.”
The consequence: Every filter adds group delay. With dynamic notch, two fixed notches, RPM filters at 3 harmonics, and lowpass filters all enabled, total group delay can exceed 10ms. At 8kHz loop rate, that’s 80 samples of delay between what the quad does and when you feel it. The fix: Start with dynamic notch and RPM filtering only. Add filters one at a time, test-fly after each one, and stop when oscillations are gone — not when every filter slot is used.
Mistake 2: Using fixed notches when dynamic notch would handle the noise.
The consequence: The fixed notch is cutting 380Hz constantly, even when the motor noise is at 500Hz. You’re filtering flight data at 380Hz for no reason because the actual noise moved. The fix: If the noise band in the spectrogram moves with RPM, a fixed notch is the wrong tool. Configure the dynamic notch range to cover that frequency window instead.
Mistake 3: Copying someone else’s filter settings without blackbox data.
The consequence: Their quad has a frame resonance at 280Hz from a loose arm. Your quad doesn’t. You just added a fixed notch at 280Hz that’s filtering your flight dynamics for no reason — and you didn’t fix the actual vibration that’s causing your oscillations. The fix: Every build has unique noise characteristics. Your filter config must be based on your quad’s blackbox data.
Mistake 4: Setting dynamic notch Q too low thinking “more filtering = safer.”
The consequence: At Q=50, the dynamic notch cuts a 100Hz-wide band. It’s removing noise effectively but the phase delay is making your quad feel like it’s flying through molasses — propwash recovery is slow and snap moves feel soft. The fix: Q=120 is a good starting point. Only go lower if blackbox shows residual noise after optimizing mechanical setup. The mechanical fix (balanced props, tight frame, soft-mounted FC) should come before aggressive filtering.
⚠️ Regulatory Notice: The flight recommendations in this article should be followed in accordance with the latest 2026 drone regulations in your country or region. Always verify local laws regarding flight altitude, no-fly zones, remote ID requirements, and registration before flying. Regulations vary significantly between the FAA (US), EASA (EU), CAA (UK), CAAC (China), and other authorities.
Notch filters work alongside RPM filtering and the lowpass filter chain. For the full picture on Betaflight’s filtering pipeline, our RPM filtering setup guide covers bidirectional DShot, dynamic notch configuration, and the complete gyro noise reduction strategy. If the noise persists after optimal filtering, the issue might be mechanical — our FPV drone noise troubleshooting guide covers the physical sources of noise that even the best filters can’t fully eliminate.
Blackbox analysis is where notch filter tuning really happens. The T-Motor F7 Pro FC’s onboard 16MB flash logs 30+ minutes at 2kHz — enough for multiple tuning sessions without downloading between flights. Combined with the Plasmatree analyzer, it’s the fastest path from “my quad oscillates” to “this thing is locked in.”