Audio Restoration
Noise reduction, hum removal and click repair all cost something; the harder you clean, the more of the original goes.
Related
The problem
Old recordings carry hiss, hum, clicks and room noise. Restoration does not aim to erase noise completely but to push it behind the music while keeping transients and timbre intact. Over-cleaned audio sounds dull or watery, as if heard through cloth.
How it works
Noise reduction usually works by spectral subtraction: estimate the noise spectrum and subtract it from the signal. A good estimate leaves little residue; a poor one removes music along with noise and leaves metallic artefacts. Hum removal targets the 50 or 60 Hz mains harmonics with narrow notches. Click repair detects transients and interpolates over them. De-essing and breath removal are different problems, and handling them in the wrong order makes things worse. Every restoration move trades lost information against remaining noise.
Settings and practice
Clean obvious events before reducing the noise floor. Sample noise from a genuinely silent stretch. Increase reduction gradually and back off one step from where artefacts appear. Notch low hum rather than treating it with broadband reduction. Repair clicks with short windows instead of smearing a whole passage. A/B against the original to confirm transients survive. Archive the untreated file and save the restored version separately.
What to listen for
On the organ's long notes, whether noise recedes without dulling the tone; on the fiddle bow, whether friction turns watery after processing; on the early piano transfer, whether pedal noise is mistaken for music. Good restoration makes you forget the noise; bad restoration makes you notice the repair.
Listen in the library
All tracks from midicn-lib — inline badge is the license tier (C1 commercial / C2 non-commercial / C3 study only).
Sources
- 谱减法与频域降噪的原理，依音频修复公开资料核对，未抄原文
- 去嗡与去咔嗒的处理顺序，依录音修复通识核对，未抄文本
Used for fact-checking only; all prose is original.