[sdiy] moog high pass flter

[harrybissell]

Hi Ian:

I agree with you, in that the HPF is more useful in 'formant' applications
than VC swept applications.  iirc didn't the ARP Odyssey have a simple
non-vc HPF ???

I'm referring to the normal "synth" use of a VCF... ie filter sweeps for
timbre modification.

A 24dB/oct HPF might be a little extreme for knocking the lower harmonics out
of a clarinet waveform.

A pulse wave can have more higher harmonics than fundamental as well....

Maybe its me. I'm a night person. Having the sun come up in the morning
depresses me. It seems like the light is going the wrong way (brighter, not
dimmer). Ditto the HPF....    :^P

H^) harry

Ian Fritz wrote:

> Actually, I've been thinking lately that HPFs are underappreciated and
> underutilized.
>
> Many acoustic instrument sounds have frequency spectra whose fundamentals
> are weaker than several of the higher harmonics.
>
> The reason for this is that the low frequencies need to be well trapped
> inside the acoustic waveguide structure in order for the non-linear engine
> that drives the sound production to operate efficiently.  What we hear is
> more like the exhaust!
>
> A pretty example of this is shown in the recent book on mathematical
> modeling of acoustic instruments edited by Hirschberg, Kergomard and
> Weinreich (Mechanics of Musical Instruments, Springer-Verlag,
> 1995).  Figure 1 of the Introduction  shows internal and external waveforms
> of a clarinet.  The internal wave is a rounded square wave, whereas the
> external waveform is extremely spikey, obviously dominated by high  harmonics.
>
> As an other example, look at the simple digital waveguide models developed,
> for example, by  J. O. Smith at Stanford.  The wave reflected from the end
> of the waveguide (back to the excitation source) is LP filtered, whereas
> the transmitted (output) wave is HP filtered.
>
> Of course, acoustic instruments have HF cutoffs, also, so LP filtering is
> indeed a natural part of music.  But HP filtering is every bit as important.
>
> It is impossible to obtain spectra with higher harmonics dominating the
> fundamental by using standard synth waveforms plus LP filtering. So unless
> you have a cool waveshaper like the Wavolver, you will definitely need to
> include HP filtering in your acoustic arsenal.
>
> As an interesting sidenote, the research done by H. Benade showed that the
> HF cutoff frequency of woodwinds is independent of pitch (in the lowest
> register).  An amazing result!  He and a student actually designed and
> built an isospectral clarinet (cutoff following pitch) and found that it
> was too dark and muffeled at low frequencies and too bright at high
> frequencies.  So non-tracking LP filtering is also an interesting synth
> programming option.
>
> At 12:20 PM 12/8/2002, harrybissell wrote:
>
> >and Hipass filters suck. oops did I say that outloud. Thats bad.. thats
> >flamebait ;^P
> >maybe blasphemy...
>
> Ignorance is what sucks, IMO.
>
> Best regards,
>
>    Ian