Dynamic Noise Limiter , DNL (abbreviation)

It was a development of the patent Philips Dynamic Noise Limiter (DNL) system, introduced in 1971, with the circuitry on a single semiconductor.

Dynamic Noise Limiter (DNL) is an unpatented audio noise reduction system originally introduced by Philips in 1971 for use on cassette decks.

Philips developed an alternative noise reduction system known as Dynamic Noise Limiter (DNL) which did not require the tapes to be processed during recording; this was also the basis of the later DNR noise reduction.