jälkikohinan

Jälkikohina is a Finnish term used in acoustics, signal processing and related fields to describe the residual noise that remains after a main signal has been removed, filtered, or transformed. The word combines jälki meaning "after" or "trace" and kohina meaning "noise", so the term literally refers to noise left behind following processing or measurement.

In practice, jälkikohina can arise from various sources, including electronic noise in sensors and preamplifiers, quantization noise from analog-to-digital conversion, and spontaneous noise in the environment that is not captured by the primary signal processing. It is commonly encountered in audio recordings after noise reduction, in measurement systems after a signal extraction step, or in communications where a channel estimate is refined but residual fluctuations persist.

Assessment of jälkikohina typically involves characterizing the noise floor and the signal-to-noise ratio of the processed output. Analysts may use spectral analysis, RMS measurements, or equivalent broadband levels to quantify the residual noise. Reducing jälkikohina generally requires improvements in hardware (larger dynamic range, lower intrinsic noise), better filtering or denoising algorithms, and careful system design to minimize coupling and external interference.

It is important to note that the precise definition and usage of jälkikohina can vary between disciplines, and in some contexts it is closely aligned with the broader concept of residual or post-processing noise. In English-language terminology, it is often described as residual noise.