Why Does FFT Show Peaks? : MALMIJAL-M Blog

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Topics include FFT vs STFT, FRF analysis, filtering techniques, and other signal processing methods used in real engineering workflows.

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Why Does FFT Show Peaks?

When you apply FFT (Fast Fourier Transform), you often see sharp peaks in the spectrum.

These spectral peaks are not random — they represent something very important.

Why Does FFT Show Peaks

What Does FFT Do?

FFT converts a signal from Time domain → Frequency domain

It tells us “What frequencies exist in this signal?”

Why Spectral Peaks Appear

FFT shows peaks because the signal contains specific frequency components.

Core Idea

If a signal has a frequency f₁, FFT will show a peak at f₁

Intuition

“FFT is like a frequency detector — it highlights what’s present”

Example: Single Frequency Signal

A pure sine wave

Only one frequency
FFT → one peak

Explanation

Only one frequency has strong energy.

sine wave, single FFT spike

Sine wave → single FFT spike

Example: Multiple Frequencies

If a signal contains

sin(5Hz) + sin(20Hz)

FFT will show

Peak at 5 Hz
Peak at 20 Hz

combined signal, two peaks

Combined signal → two peaks

Why Spectral Peaks Are Sharp

Spectral peaks are sharp because energy is concentrated at specific frequencies.

Key Insight

Strong frequency → high peak
Weak frequency → small peak

What Affects Peak Shape?

1. Signal Length

Longer signal → high frequency resolution → sharper peaks

2. Windowing Effect

Poor window → spectral leakage
Spectral peaks become wider

3. Noise

Adds small random peaks

Frequency Domain Interpretation

FFT peaks represent

Frequency location → where peak is
Magnitude → how strong it is

Important

Peak height = signal strength at that frequency

MALMIJAL Workflow

FFT Analysis

Generate/Load a signal
Apply FFT
Identify peak's frequency

Generate signal

Generate signal

Apply FFT

Apply FFT

Identify peak's frequency

Identify peak's frequency

Key Takeaways

FFT peaks = frequencies present
Peak position = frequency
Peak height = strength
Multiple peaks = multiple frequencies