[sdiy] Low Pass filters and musically useful frequency range

[Andrew Simper]

On 7 May 2014 04:16, David Ingebretsen <dingebre at 3dphysics.net> wrote:
>
> Thanks Tom,
>
> I think I confused the issue with the "10 Hz" comment. The filter actually
> hits everything below about 40 to 60 Hz which is what is curious to me. Why
> not make it 20 Hz? Why make it something around 40 to 60Hz?
>
> David
>

Hi David,

I think you have to ask yourself what is the 914 designed to do? Have
a "reed" of this: http://www.moogarchives.com/m914.htm and you can see
that it is a formant style filter, so it is designed to emulate the
resonant bodies of physical instruments, in the notes is specifically
mentions double reeds. Consider a double bass, it has the lowest
string tuned to E1 (41 Hz), but the lowest resonant peak of the body
is around 120 Hz, and the high pass nature of the rest of the formant
needs a high pass cutoff of around 60-80 hz:
https://courses.physics.illinois.edu/phys406/Student_Projects/Spring12/Michael_Zevin_P406_Project_Report_Sp12.pdf

This is not a full track master eq product, it is designed to impart a
formant shape on some basic buzzing tones to make them sound more like
a physical instrument.

Andy