Audio Feature Extraction with Librosa

Librosa is a Python package for music and audio analysis. It provides tools to load audio, visualize waveforms and spectrograms, and compute features used in analysis or machine learning. Common choices include short-time Fourier transform magnitudes, mel spectrograms, mel-frequency cepstral coefficients, chroma features, spectral centroid, and onset strength. Each feature summarizes different aspects of the signal rather than providing a universal descriptor.

MFCCs compress the spectral envelope into coefficients using a mel-frequency filter bank and a cosine transform. They are widely used in speech and audio tasks but may discard details useful for other applications. Chroma features fold spectral energy into pitch classes, often twelve semitone classes, which can support harmony-related analysis. Onset strength summarizes changes associated with likely musical or acoustic attacks; it is not a guaranteed event detector.

Feature extraction depends on framing choices. The sample rate determines how samples map to time and frequency. Window length controls the local analysis span; hop length sets spacing between frames and affects temporal resolution. Centering and padding influence frame timestamps near boundaries. If audio is resampled, the waveform itself must be transformed. Loading as mono, choosing a target sample rate, or preserving stereo channels changes the data available to features.

For machine learning, preprocessing should be consistent between training and inference. Fit normalization statistics on training data only. Split source recordings, speakers, or sessions before creating overlapping windows so near-duplicate frames do not leak into validation. If a model consumes sequences, document frame dimensions and feature ordering. Evaluate features on the target task rather than assuming conventional features always improve performance.

Librosa's defaults and APIs can evolve, so pin versions for reproducible pipelines. Test file decoding, channel behavior, duration handling, and numeric ranges on representative audio. Feature plots support interpretation, but a visually clear spectrogram does not establish that the model will generalize.