spec: add spectrogram-basic specification

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New Specification: spectrogram-basic

Related to #2927

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specification.md

spectrogram-basic: Spectrogram Time-Frequency Heatmap

Description

A spectrogram displaying time-frequency representation of a signal as a heatmap. It shows how the frequency content of a signal changes over time, with color intensity representing the amplitude or power at each time-frequency point. Essential for analyzing non-stationary signals where frequency characteristics vary, revealing patterns invisible in time-domain or frequency-domain views alone.

Applications

• Audio analysis including speech recognition and music processing
• Vibration monitoring for machinery health and fault detection
• Seismic data analysis for earthquake and geological studies
• Biomedical signal processing such as EEG and ECG analysis

Data

• signal (numeric array) - time-domain signal values
• sample_rate (numeric) - sampling frequency in Hz
• Size: 1000-50000 samples for clear visualization
• Example: chirp signal with increasing frequency, audio waveform, or vibration data

Notes

• Use a perceptually uniform colormap (viridis, inferno) for accurate magnitude representation
• Include colorbar with power/amplitude units (dB scale often preferred)
• Label axes clearly: time (seconds) on x-axis, frequency (Hz) on y-axis
• Consider log scale for frequency axis when spanning multiple octaves
• Window size and overlap affect time-frequency resolution trade-off

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