noise-reduction

Noise reduction is a specific kind of signal processing — techniques (filtering, spectral subtraction, wavelet denoising, etc.) applied to reduce unwanted noise while preserving the desired signal.

Noise reduction operates on signals using signal processing techniques (filtering, spectral subtraction, FFT-based methods). Remove signal processing and noise reduction stops operating — present-tense operational dependency (Law 8). The edge-test confirms signal-processing is the older/more-foundational concept.

Per Law 8d: spectral subtraction is designed and maintained specifically for the purpose of reducing noise from signals. Its entire algorithm — estimate noise spectrum, subtract it, reconstruct — is aimed at noise reduction as its goal. The technique exists to serve the noise-reduction objective.

Per Law 8d: cepstral subtraction is a noise reduction technique operating in the quefrency domain. Its designed purpose is to attenuate noise by subtracting noise estimates in the cepstral representation. It exists to serve the noise-reduction objective.

Cepstral subtraction IS a specific kind of noise reduction. It operates in the quefrency domain, estimating and subtracting noise components from cepstral coefficients. Nearest kind: noise-reduction.

Noise reduction techniques predate audio restoration as a practice. Audio restoration emerged from and built upon noise reduction methods — the historical sequence is clear: noise reduction came first and fed into the broader practice of audio restoration.

Audio-denoising IS a specific kind of noise-reduction — it is noise-reduction applied to the audio domain. A competent speaker would say 'audio denoising is a type of noise reduction.' Files against nearest kind (noise-reduction exists; signal-processing would be one rung further up the ladder).

Spectral gating is a specific noise-reduction technique that attenuates frequency bands below a time-varying threshold; it is a particular kind of noise reduction, not a separate field. The definition pins spectral gating as a technique within the noise-reduction family.

Dithering is a specific technique for reducing perceived quantization noise, a particular kind of noise-reduction practice applied in digital audio.

Law 8d for-whose-sake test: a noise gate is built FOR THE SAKE OF reducing unwanted noise — its own accepted definition states the purpose: 'reducing background noise between intentional sound events.' The servant points at the master: the gate is the means; noise-reduction (the accepted category carving attenuation of the noise component while preserving the desired signal) is the end it serves. Pinned sense: gate-as-serve-notice-of-the-noise-reduction-end. Not DEPENDS_ON (the gate operates without the category existing as an entry — a purpose is never a functional component, Law 8c) and not INSTANCE_OF (a simple gate does not meet the noise-reduction definition's statistical-estimation requirement — it attenuates below a threshold, it estimates nothing). Same shape as accepted technique-serves-application edges (mel-cepstral-distortion SERVES speech-recognition).

Spectral whitening is built for the sake of noise reduction pipelines. It prepares signals by flattening their spectrum, removing spectral coloration that would otherwise bias noise estimation and reduction algorithms. The arrow points from the servant technique toward the master goal it serves.