# FFT Frequency Peaks First Pass

Use a simple FFT-style frequency view to spot repeated patterns in audio, vibration, motor, sensor, or SDR-like logs without overclaiming the cause.

## Outcome
Compare a time signal with a frequency view and identify one dominant repeating pattern.

## Safe first step
Write the sample rate, units, recording length, sensor or source, and expected pattern before reading frequency peaks.

## Ladder steps
### 1. Capture the time signal
Start with the actual samples: audio level, vibration value, motor current ripple, SDR audio, or game signal.

Check: Your note names units, sample rate, duration, and source.

### 2. Check the sampling limit
The Nyquist limit is half the sample rate, so higher frequencies may fold into misleading lower clues.

Check: You can say which peaks are inside the trustworthy first-pass range.

### 3. Compare strongest peaks
Read the largest and second largest frequency components before deciding what deserves attention.

Check: Your note lists peak, second peak, amplitude clue, and noise caution.

### 4. Turn the peak into a next test
A peak should point to a repeat measurement, not a confident cause claim.

Check: You can write what setup, sensor, or sample window you would change next.

## Examples
### Find a repeated pattern
```sh
time samples -> frequency bars
```
Expected signal: The frequency view shows which repeating components are strongest

Caution: A short sample can blur or exaggerate peaks.

### Decide which peaks are inspectable
```sh
sample rate -> Nyquist limit
```
Expected signal: Frequencies above half the sample rate are outside the first-pass trust boundary

Caution: Aliasing can make a high frequency look like a lower one.

### Turn a peak into a repeat test
```sh
peak + context -> hypothesis
```
Expected signal: The strongest peak becomes a clue to test again with context

Caution: Do not turn one noisy peak into an exact diagnosis.

## Common traps
- Ignoring sample rate and Nyquist before trusting a frequency label.
- Treating one peak as proof of an exact failing part.
- Comparing recordings with different units, mounting, window length, or sensors.
- Forgetting that a short sample can smear or hide nearby frequencies.
- Deleting the time signal and keeping only the biggest bar.

## Practice task
Use the widget to create two tones, change sample rate once, copy the note, and explain which peak is useful and what remains uncertain.

## Next steps
- Save the Obsidian note with [[FFT]], [[Frequency]], [[Sample Rate]], [[Nyquist Limit]], [[Aliasing]], [[Sensor Log]], [[Audio]], [[Vibration]], [[SDR]], and [[Noise Floor]] backlinks.
- Use sensor statistics if the raw signal is noisy before frequency analysis.
- Use calculus when the signal came from position, velocity, or acceleration over time.
- Use trigonometry when the frequency clue ties to rotating parts or sweep angles.
- Repeat the measurement before making a build decision.

## Related
- [Applied data routes](/topics/data/)
- [Basic statistics for sensor logs](/learn/data/basic-statistics-for-sensor-logs/)
- [Calculus for game motion](/learn/math/calculus-for-game-motion/)
- [Trigonometry for rotation and layout](/learn/trigonometry-for-rotation-and-layout/)
- [SDR flight tracking first pass](/learn/rf/sdr-flight-tracking-adsb-first-pass/)
- [Build a first Godot game loop](/projects/build-first-godot-game-loop/)
- [Turn a source video into notes](/video-notes/)
- [Review Anki-compatible decks](/decks/)

## Obsidian backlinks

Use these wiki links to connect this note inside a local maker vault:

- [[TopicLadder]]
- [[Maker Learning]]
- [[FFT Frequency Peaks First Pass]]
- [[Applied Data]]
- [[data]]
- [[signal-analysis]]
- [[Capture the time signal]]
- [[Check the sampling limit]]
- [[Compare strongest peaks]]
- [[Turn the peak into a next test]]
- [[Applied data routes]]
- [[Basic statistics for sensor logs]]

## Source and next routes

Source: https://topicladder.com/learn/data/frequency-peaks-first-pass/

- [Applied data routes](/topics/data/)
- [Basic statistics for sensor logs](/learn/data/basic-statistics-for-sensor-logs/)
- [Calculus for game motion](/learn/math/calculus-for-game-motion/)
- [Trigonometry for rotation and layout](/learn/trigonometry-for-rotation-and-layout/)
- [SDR flight tracking first pass](/learn/rf/sdr-flight-tracking-adsb-first-pass/)
- [Build a first Godot game loop](/projects/build-first-godot-game-loop/)
- [Turn a source video into notes](/video-notes/)
- [Review Anki-compatible decks](/decks/)