Low pass gate

A Low Pass Gate (LPG) is combination of Low Pass filter (LPF) and VCA based on one of Don Buchla's designs. Often LPGs can be switched between low pass and VCA modes, i.e. three modes of operation when the LPG mode is counted, although the module may act only as a filter/LPG or some other more limited combination.

The real wonder of an LPG only become fully apparent when in actual LPG mode - a combined LP+VCA mode in which the sound becomes brighter as the loudness increases. This 'colouring' of the VCA action by the LPF is generated using a component called a vactrol - an electronic device which transfers electrical signals using light waves to 'bridge an electrical gap' between its input and output, which has a slow enough response as far as electronics are concerned that it has an audible effect on the timbre of the output sound.

Some LPGs employ a resonant LPF which can impart even more colour to the sound, although the classic Buchla LPG sounds such as the "Buchla Bongo" rely on FM, Waveshaping/Folding or distortion to create a richer spectrum of sound to the input, allowing more scope for the filter to add colour as it opens, allowing harmonics/other extra audio frequencies through.

Feel free to add to this list. See also: Modules by Function

Euro

Manufacturer	Module	Width	Power	Comment	Product Page
Doepfer	A-101-2	8hp	20mA	Vactrol Low Pass Gate	A101-2
Makenoise	QMMG			Quad Multimode Gate

5U

Manufacturer	Module	Width	Power	Comment	Product Page
MegaOhm Audio	CdS VCF/A	1 U	+/- 15V		[CdS]

Frac

Manufacturer	Module	Width	Power	Comment	Product Page

Buchla

Manufacturer	Module	Width	Power	Comment	Product Page
Buchla and Associates	292e Quad Dynamics Manager	1	???	Quad LPF/LPG/VCA with mixer	292e

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Sub-section	Filter	Modules by function
Related	How to 'Ping' a filter	LPG