[sdiy] moog high pass flter

[Gavin]

i think High Pass is incredible.  particularly on the Yamaha CS synths.  The
reason someone who's experience with the Moog High Pass might not be so into
high pass is most likely because the moog ladder or the ssm2040, basically
the same filter, is extremely rich in the low end, but very weak in the high
end.  I think the fault is in the filter, not the mode... check it out
----------
>From: Ian Fritz <ijfritz at earthlink.net>
>To: harrybissell <harrybissell at prodigy.net>, benno <benj at iinet.net.au>
>Cc: synth-diy at dropmix.xs4all.nl
>Subject: Re: [sdiy] moog high pass flter
>Date: Sun, Dec 8, 2002, 9:56 PM
>

>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
>