ar ffb, grayscale euro panel, 28hp
this is the euro panel for the analogue realities 914 fixed filter bank module
panel design by grayscale
the fixed filter bank is david ingebretsen's reinterpretation of the classic fixed filter bank.
more information here: http://analoguerealities.com/projects/fixed-filter-bank-914/
"First, I have to give credit where it’s due for the inspiration.
Dr. Moog and his engineers for the original design.
Yves Usson for his work, design, and idea to break out even and odd cells.
Jurgen Haible (R.I.P.) for his approach using simulated inductors (GIC)¹.
My design clearly derives from the original Moog™ design and is as faithful to that design as possible. I spent more time pouring over those simple filter circuits more than any other project I’ve undertaken. Hours of simulation in MultiSim trying to characterize the circuit. Staring at photos and trying to trace signals and identify components. Finally realizing a resistor was missing which made all the difference because the resistor directly helps determine the “Q” of the cells. Then the reward of simulations that produced the proper frequency response and prototypes that finally worked the way they should with very little noise or hum. Last, dealing with some form and fitment issues so that the module could reasonably be built. What a trip.
So, thank you Dr. Moog, Yves, Jurgen, and any teacher or author who taught me, and especially my dad who taught me to love electronics as soon as I could hold the solder for him while building Heathkits.
The project is not cheap. Plan on $300.00 or a little more for inductors, and depending on what you choose, as much as $130.00 for op amps (see below). The GIC version is pretty straight forward to build and probably more robust if you gig your synthesizer. The inductor version clearly will be more true to the original, but soldering the extremely fine varnish coated wires and getting a solid solder joint takes patience and care. The cores are a bit brittle and fragile and care must be used when mounting them. In the end though, you will have an extremely useful and unique module for sound shaping.
Don’t hesitate to ask questions or give me feedback. I don’t do this to make money. I just want to help you make the music that I don’t have the talent to make myself.
This module is not an equalizer but it does boost and attenuate in frequency bands, so it is an equalizer. Honestly I don’t know what to call it. Reading the information I could find, mostly from the MoogArchives.comwebsite (the following is in part paraphrased from the Moog™ docs reproduced there), this filter is a non-voltage controlled “modifier” with 14 band pass filters with a control which adjusts the level of each band. Each band has a 12dB slope. This creates peaks and troughs similar to a formant filter. There is also a low pass band and a high pass band.Each band has a “Q” of about 3.7 (thank you Yves for that tidbit). I think the intent was specifically for it to be not voltage controlled so that the timbre of an input signal would change as it moved through the frequency regions. One use might be to help replicate the fixed resonances of a particular real instrument, or for creating other unique effects by emphasizing certain bands mixed with an unfiltered signal.
A modifier module, typically in near the end of the signal path before final mixing, but it can go anywhere you have an audio signal to process. It is ultimately AC coupled so it is not of much use for CV processing. You can use the filter as an “all pass” filter and send the even signal to one stereo channel and the odd signal to the other for an interesting pseudo stereo effect.