Taking the Bi Filter Follower a step further

Started by StephenGiles, May 04, 2005, 04:50:24 PM

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StephenGiles

I've just been looking at this circuit on Mark Hammer's site, (Mark - I needed the Guitar to Synth Interface article for something else I've been pondering and the floppy disc containing my scan has gone pear shaped!).

Now, consider the Bi Filter with a separate sweep controller for each filter. Would it then be possible to get a more vocal type of sound do you think? I'd be interested to see some views on this.
Stephen
"I want my meat burned, like St Joan. Bring me pickles and vicious mustards to pierce the tongue like Cardigan's Lancers.".

Mark Hammer

Well, I was about to try the transistor replacement, as per Jack Orman's suggestion, on the Dr Q x 2 that I perfed, but now that you mention it, I have 3 of the BiFilters perfed and working, so if the transistor experiment doesn't work I may give the  BiFilters a go.

The one caveat I think needs considering is that if, as my hunch suggests, discrepant timing of sweeps plays a role in vocality, the inherent lag/decay time of the CLM6000's may well undermine that, since there are clearly limits on how fast they can be made to sweep.  Slow isn't an issue; but fast IS.

I appreciate the idea, though, and whether it gets done tonight or later, I'm sure it will be pursued.

StephenGiles

Hi Mark, I'll be trying this in the next few days - it doesn't look as if it appealed to anyone else yet!!!!!!! Do you have a decent scan of the PE Light Metal? I can't find my original article.
Stephen
"I want my meat burned, like St Joan. Bring me pickles and vicious mustards to pierce the tongue like Cardigan's Lancers.".

moosapotamus

Seprate sweep controllers, cool idea, Stephen. I think it would open up a lot of possibilities for getting some unique sounds.

How would you do it... separate sidechains, opposing sweep directions, different optos, quadrature oscillator, lead-lag type stuff, lfo modulation on one side combined with envelope follower on other, other possibilities?

~ Charlie
moosapotamus.net
"I tend to like anything that I think sounds good."

Mark Hammer

Steve,

I'm sure I have a Light Metal pdf somewhere, which means I must have gotten it electronically somewhere from someone.  I'll try and dig around for it this evening.

Charlie,

There are two aspects to tinkering with the sweep of the filter sections.  One aspect is the actual envelope signal fed to each optoisolator, and the other is the amount of travel induced in each case.

With regard to the second one, note that the LDR is simply a resistance.  One is always free to stick a second resistance in series with it (to set a limit on minimum R achievable), and a third resistance in parallel with it (to set a limit on maximum R achievable).  These two additions can change how much the one filter section "travels" in response to a pluck, as well as where it travels, relative to the other filter section.  I might point out that this can be helpful in adapting dual-filter units to suit bass.  If the lower filter is essentially on a shorter tether, and less "free to wander", in comparison to the upper filter, then more of the meat of bass notes is retained, without thinning out too much, while the more extensive wandering of the upper filter section allows for variation in harmonic content.  There is absolutely no need for both filter sections to sweep the same amount at the same time.

So far, my experiment with two half-wave rectifier sections being driven by the same gain stage (Dr Q x 2) is not exactly thriving.  The intent was to have different time constants for each filter.  Perhaps a different format is needed.  In the case of the BFF, note that the two optoisolator LED sections are driven from the same envelope-follower gain stage and rectifier, but each LED has its own 1k current-limiting resistor.  It may well be possible to precede each 1k resistor with its own diode/resistor/cap-to-ground combo, to produce different sweep characteristics for each section.  If you are a fan of the Mutron, I encourage you to try out a resistor of 47-68R, instead of the 470R value shown, and a 47uf cap instead of the 100uf shown.  Speedier and more dramatic, though obviously less well-suited to some styles of rhythm playing.

StephenGiles

What about sticking one sweep through a long BBD?
Stephen
"I want my meat burned, like St Joan. Bring me pickles and vicious mustards to pierce the tongue like Cardigan's Lancers.".

puretube

the "Sweep-Thru-Procrastinator"...
for 10 sweeps per second, Nyquist sez: clock>20Hz;
calling all math-freaks: what`s the max delta-T with a MN3207 @ 51.2Hz ?
:wink:

hank reynolds 3rd

i had an idea of splicing the bi filter/follower (with mods for the range caps on a switch) with the royal filter's sweep control (and a 'sensitivity' pot) as they both use ldr/leds....
haven't designed a pcb yet, but it's something i'm thinking of building.....
oh...and a resonance control for each of the filters ( i got this idea from the fuzzyballs schem that someone designed...i think they guy was called marjen...)

just thought i'd add a few thoughts


Sam

StephenGiles

Ah but you wait for the "Camilla" filter, that is swimming around my head!
Stephen
"I want my meat burned, like St Joan. Bring me pickles and vicious mustards to pierce the tongue like Cardigan's Lancers.".

R.G.

Remember that filter performance and "vocality" are different things.

Vocality happens in the listener's brain. Our brains have set up pattern recognizers for picking out sounds with peaks at the vowel hot spots. See the vowel formant chart at GEO at http://geofex.com/Article_Folders/wahpedl/voicewah.htm or one of the several on the web for which these are. More to the point, the brain recognizes specific combinations of filter centers as a vowel. It takes a minimum of two filters in the right place to get a vowel.

Simply sweeping one filter center up while the other sweeps down will not necessarily hit many vowel sounds, although it will probably hit a couple.

To get a sequence like oo- aw- ah- ae- e- i - ee you need to move the formants like

F1 300 550 900 1000 700 500 300

F2 800 800 1400 2000  2200 2350 2500

simultaneously, pairwise. F2 starts low and sweeps slow, then rises fast and then rises slowly. F1 starts low, goes up, flattens then comes back down.

The more places in the sweep that the filter centers cross the vowel areas the more times it sounds like a vowel. Places outside the vowel areas sound like tones, but they are not recognized as vowels.
R.G.

In response to the questions in the forum - PCB Layout for Musical Effects is available from The Book Patch. Search "PCB Layout" and it ought to appear.

hank reynolds 3rd

stephen..
I was thinking of calling the aforementioned design camilla also.....like the royal filter with TEETH (honestly!!!)...
very mystic meg...
:D

Mark Hammer

Quote from: R.G.Remember that filter performance and "vocality" are different things.

Vocality happens in the listener's brain. Our brains have set up pattern recognizers for picking out sounds with peaks at the vowel hot spots. .... It takes a minimum of two filters in the right place to get a vowel.

The dual phaser that Mike/Vsat linked to over at Scott Bernardi's site (see the TZP thread currently running) has a sound sample that is eerily vocal-like in quality.  It reminds me of some of the voice-like sounds that Isao Tomita got on the old "Snowflakes are dancing" track from decades back.

Peter Snow

Quote
oh...and a resonance control for each of the filters ( i got this idea from the fuzzyballs schem that someone designed...i think they guy was called marjen...)

His name is Marjan Urekar and this is his website: http://members.tripod.com/urekarm/synth/fuzzyballs.html
It does not appear to have been updated in a long time.  
Marjan used to belong to the SDIY list but I have not seen any postings from him for quite a while.
Remember - A closed mouth gathers no foot.