Wiardgroup

I posted a couple examples of my OmniFilter in the Files section (OmniFilter examples folder). 
The filter really seems to lose a lot of output when entering the bandpass mode (very 
noticeable in the 24dB output file). The module is processing a sawtooth wave. Coarse, Fine, 
and Q are @ 12 o'clock. I'm manually turning the filter mode knob from LP to AP and back 
again a few times. It worries me a bit, since my Borg I filters have a consistant output no 
matter what mode they're in. Any comments? Or am I just not getting it? (very often the 
case ;-)

-andrew bunny

Hi Andrew
my 'Omni' is a very early 'The Filter' version that i've chosen to
keep un-updated. At relatively low-Q settings, when i sweep through
bandpass mode, the lowest amplitude is consistently bandpass mode. The
 decrease is not as pronounced as in your example but there is a
distinct decrease. Your post is sort of weirdly synchonous in my life
because i just delivered a lecture on filter modes in one of my
classes on Wed. night. i use an EMU UAF and an Aries 327 for demos and
 i always point out that a bandpass function (without a lot of
resonance added in) physically passes the -least- energy because it's
lopping off the energy both above AND below the corner frequency. Many
designs use clever schemes to makeup the gain** but those venerable
old state variables just do the cutoff and let chips fall where they
may. (that's why they're good for demos!) i don't know how Grant
implemented the bandpass in the Omni nor can i tell you that your
decreased gain is 'normal' but i can tell you that in a raw filter
circuit , with all other factors being equal, bandpass is the mode
that passes the least audio energy.
As for the Borg, the slopes are way shallower than the 4-pole Omni and
the circuit is of a vastly different type. While i'm not certain, i
suspect that the Borg's slope varies as one sweeps through the modes,
in a way that makes the 'band-PASS' mode more of a 'band-emphasize'
that leaves a lot of unattenuated audio on either side of the center
freq. 

best,
-doc 

** maybe even not so clever, because a classic state variable has
separate outputs for each mode. Its a simple matter to simply boost
the gain of the bandpass output with an opamp until it's commensurate
with the other modes.Since the Omni doesn't separate the outputs this
scheme is precluded


--- In wiardgroup@yahoogroups.com, "andrew dalio" <bunnyman@...> wrote:
>
> I posted a couple examples of my OmniFilter in the Files section
(OmniFilter examples folder). 
> The filter really seems to lose a lot of output when entering the
bandpass mode (very 
> noticeable in the 24dB output file). The module is processing a
sawtooth wave. Coarse, Fine, 
> and Q are @ 12 o'clock. I'm manually turning the filter mode knob
from LP to AP and back 
> again a few times. It worries me a bit, since my Borg I filters have
a consistant output no 
> matter what mode they're in. Any comments? Or am I just not getting
it? (very often the 

> case ;-)
> 
> -andrew bunny
>

I really appreciate this post because it caused me to give some "deep thought" to the 
question.

I'll try to be brief.

As terminology is borrowed from one field to another, it meaning often changes.

Electronics engineering borrowed terminology from acoustics, and electronic music 
borrowed terminology from engineering.

Resonance, Q (quality), regeneration, peaking, negative feedback and positive feedback all 
have specific technical meanings. Subjectively, they can all be grouped under "resonance".

Instrument designers walk a line between two worlds and it can get confusing what to call 
something. Use the correct technical or historical name or use a popular subjective name.

The Omni-filter bandpass mode is technically correct, the Borg filter bandpass mode is 
actually a "simulated resonator". It only adds gain at the corner frequency and doesn't 
subtract anything. This is subjectively the way musicians want it. The Omni-filter subtracts 
everything but the central frequency, technically correct, but more difficult to apply 
musically.

To explain the difference I would have to get into DC response, AC response, passband 
gain, corner frequency gain and corner frequency phase response. Which I am way too 
busy to do.

Let's put it this way, when musicians talk about "subtractive synthesis" they really want to 
subtract in very specific ways. Ways that do not change the apparent "volume" of the 
sound (particularly bass volume). But mathematics is against that, and so engineers have 
to be very clever to come up with filter designs that behave subjectively correctly to 
musicians.

The Omni-filter was my first design. Later, based on what musicians told me, I designed 
filters that behave much more the way musicians prefer. Both types are "correct", but the 
later designs (Borg 1 and 2, Boogie) are specifically designed for electronic music use.

Hope that helps.

--- In wiardgroup@yahoogroups.com, "andrew dalio" <bunnyman@...> wrote:
>
> I posted a couple examples of my OmniFilter in the Files section (OmniFilter examples 
folder). 
> The filter really seems to lose a lot of output when entering the bandpass mode (very 
> noticeable in the 24dB output file). The module is processing a sawtooth wave. Coarse, 
Fine, 
> and Q are @ 12 o'clock. I'm manually turning the filter mode knob from LP to AP and 
back 

> again a few times. It worries me a bit, since my Borg I filters have a consistant output no 
> matter what mode they're in. Any comments? Or am I just not getting it? (very often the 
> case ;-)
> 
> -andrew bunny
>

Many thanks to Doc and Grant for the replies. In case anyone gets the wrong idea, I want 
to say how much I enjoy the sounds of the OmniFilter! Heck, I also deeply love my Borg, 
Waveform City, and Wogglebug. Wish I had the dinero to get some of the newer modules, 
too!. Anyway, no disrespect to the sound of the filter, which is lovely; just glad to realize 
that it's SUPPOSED to have the _perceived_ volume decrease.

-andrew bunny

--- In wiardgroup@yahoogroups.com, "Grant Richter" <grichter@...> wrote:
>
> I really appreciate this post because it caused me to give some "deep thought" to the 
> question.
> 
> I'll try to be brief.
> 
> As terminology is borrowed from one field to another, it meaning often changes.
> 
> Electronics engineering borrowed terminology from acoustics, and electronic music 
> borrowed terminology from engineering.
> 
> Resonance, Q (quality), regeneration, peaking, negative feedback and positive feedback 
all 
> have specific technical meanings. Subjectively, they can all be grouped under 
"resonance".
> 
> Instrument designers walk a line between two worlds and it can get confusing what to 
call 
> something. Use the correct technical or historical name or use a popular subjective 
name.
> 
> The Omni-filter bandpass mode is technically correct, the Borg filter bandpass mode is 
> actually a "simulated resonator". It only adds gain at the corner frequency and doesn't 
> subtract anything. This is subjectively the way musicians want it. The Omni-filter 
subtracts 
> everything but the central frequency, technically correct, but more difficult to apply 
> musically.
> 
> To explain the difference I would have to get into DC response, AC response, passband 
> gain, corner frequency gain and corner frequency phase response. Which I am way too 
> busy to do.
> 
> Let's put it this way, when musicians talk about "subtractive synthesis" they really want 
to 
> subtract in very specific ways. Ways that do not change the apparent "volume" of the 
> sound (particularly bass volume). But mathematics is against that, and so engineers 
have 
> to be very clever to come up with filter designs that behave subjectively correctly to 
> musicians.
> 
> The Omni-filter was my first design. Later, based on what musicians told me, I designed 
> filters that behave much more the way musicians prefer. Both types are "correct", but 
the 
> later designs (Borg 1 and 2, Boogie) are specifically designed for electronic music use.
> 
> Hope that helps.
> 
> --- In wiardgroup@yahoogroups.com, "andrew dalio" <bunnyman@> wrote:
> >
> > I posted a couple examples of my OmniFilter in the Files section (OmniFilter examples 
> folder). 
> > The filter really seems to lose a lot of output when entering the bandpass mode (very 
> > noticeable in the 24dB output file). The module is processing a sawtooth wave. 
Coarse, 
> Fine, 
> > and Q are @ 12 o'clock. I'm manually turning the filter mode knob from LP to AP and 
> back 
> > again a few times. It worries me a bit, since my Borg I filters have a consistant output 
no 
> > matter what mode they're in. Any comments? Or am I just not getting it? (very often 
the 

> > case ;-)
> > 
> > -andrew bunny
> >
>