Fixed Filter Banks

 I love Fixed Filter Banks.

They are a beautiful way to process audio. There are many types in lots of formats.

 

Some of the earliest appeared in the Buchla & Moog formats.

 

This is a Buchla 194.

Probably from around 1969 ????

... maybe early 1970s ??

 

A filter bank is an array of bandpass filters. 

They separate the input signal into multiple components.

Each channel carries a single frequency sub-band of the original signal. 

 

The process of splitting the signal is called "analysis".

The output of analysis is referred to as a subband signal.

This output of each channel is then recombined. This process is referred to as synthesis.

Notice that the 194 doesn't have a level/vol control for any bands.

Nor does it have a summed output.

This is a Buchla 195

It's a 10 band fixed filter.

The 194 above is a 4 band filter.

Neither filter has level controls. I usually patch these into a mixer.

 

Moog of course produced the other very famous fixed filter

The venerable 907

 

 Usually, filter banks consist of a low pass filter on the lowest band and a HP on the highest band.

Between these there are bandpass filters.

 

  It's really simple. The 907 has just one input & one output.

Unlike the Buchla 195 & 195, there are level controls for each band.

The Moog 907 is a 10 band filter. The Moog 914 consists of 14 bands. 

 

 

The Buchla 194 & 195 belonged to Don's first modular synth .. the Buchla 100

 These modules developed in his Buchla 200 system.

On the left is a Buchla 294.

 

Notice the level controls for each band, plus a summed output.

 

 

The path of evolution didn't stop here for Don.

He went on to produce the Buchla 296.

There are now 16 channels.

 

Don named the 296 the "Spectral Processor" as it allows you to do a spectral analysis of an audio

signal. The module generates corresponding control voltages of  each band. There are also envelope followers

for each band. 

Two of these can be patched to form a vocoder.

In the early 2000s Don developed the 200e. And along came the 296e.

Each band has a touch sensitive plate and all setting can be store and recalled.

 

You don't need to be rich to have a taste of these filters.

There are plenty of examples in the Euorack format

 

 

This is of course based on the original Serge Resonant equaliser

 

Great for feedback looping

 

 

This is a Mooger Fooger guitar pedal.