You probably use the filters on your synths all the time, but how much do you really know about them? This guide will make you a filter expert...  

The Basics

The Transistor Ladder Filter

The Moog Ladder Filter Schematic, as submitted to the US Patent Office

Diode Ladder Filter

The EMS VCS3 Putney was one of the first synths to use the Diode Ladder Filter which later became part of the iconic sound of the Roland TB-303

Sallen-Key Filter

Two Korg35 chips nestled in a Korg MS20

Operational Transconductance Amplifiers (OTA Filters)

Further Filter Fundamentals

Marc Doty and the Moog Foundation go deep into Filters and Synthesis in this excellent course in the AskAudio Academy. 
Watch Marc Doty and the Moog Foundation go deep into Filters and Synthesis in our excellent video course in the AskAudio Academy. 

Scott is a Sound Designer from Vancouver, Canada who has contributed his post production audio skills to dramatic and documentary films, animations, video games, and oddly enough, the Chevrolet Volt. His music makes heavy use of field recordings gathered from a variety of sources and locations. In 2013 he released Sonidos De Cuba, an a... Read More


David A Frederick
Can you tell me what kind of filter was used in the 1976 CAT synthesizer? Thank you. please email me your answer.
David A Frederick
can you tell me what kind of filter was used in a 1976 CAT synthesizer. Was it a 2040?
Scott Riesterer
Hi David,

According to this thread, originally it had a 4-pole filter using 4 CA3080 OpAmps then later switched to a 2040. Both were cascaded OTA filters to avoid the Moog transistor ladder patent.

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