MIDIBOX CV Modular (FilterBank/Switcher/Synthsizer) - %20 Panel Art & Schem..

[Artesia]

hmm... new topic catogory weee ! :)

Just nothing that ive got some of the peliminary hardwardware built to start experimenting with making a self contained, Filter bank Controlled by the usual CV modules ...however also integrating signal switching/routing to facilitate full automation and recall of setups.

The intention of this project is to create a modular system; which pretty much any combination of filters and other cv compatable hardware can be dropped directly into the rack case... And be selected for hooking into a pc as a 'Hardware Plugin' ..by using a multichannel soundcard in duplex mode to send sound out for processing & capture the result at the same time. an equal number of ins and outs would be nice ie 16in/16out.. 8in/8out.. even 2in/2out... if the budget wont strech far enough !

(infact, theres no reason for that matter, why this couldnt be used to build a complete stand alone modular analog synth with full routhing and automation too.. just a choice of modules)

Currently Have built one of the CV modules; fully working (+ oled display ;) ) ...with another to finish ...see shabby cam pic below:

And am in the process of finishing building afew analog filters... Everything will be mounted into a temporary case whilst all the really tedious tinkering happens..

Not on a mad rush with this one, quite yet (need to learn some rudimentry code for hacking mios for one) ...so dont expect results too soon...

Tho any input and discussion on the matter is welcome..

Things that need defining and refining to make this work properly (as well as prove useful for other projects).. Are tracking down appropriate parts to make affordable Signal switchers (absolutely mandatory!)  & also a viable way to multiplex CV channels ..or at least make CV channels cheap somehow ! (some of this discussed elsewhere..)

As a side issue, may need to use transconductance opamps to CV'ify various (filter, etc) controls which where not setup for this originally. ...other option of using digitally contrrolled resistors (PGA chips) probably wont work in most instances... introduce artifacts & further complicate the hardware involved. ...reasoning to the contuary welcome of course :)

The idea being to avoid the need to manually set anything (front pannel should be a collation of blinking lights at the most ;) ...realtime control can be done through a Midi control surface if it is needed :)

Anyways thats all for now.

UPDATE:

Current INITIAL panel design... with some further refinements and explaination to come ...have started moddding the case already ..btw this is a smoked perspex bonanza ;)

(Raised front bezel comes forward by 1/2 inch - Case from Scrap Recycled, HP Infered Laser source/psu)

Scematic of internal workings,

eight channels of audio in and out (provided by a maudio 1010lt), filters/cv controllable analog thingys grouped togeather in (8) banks of 4. only one 'filter' selectable per an audio channel, two cvs & hard wired trigger can be used where nessusary (ie when installing a VCO).

An audio/router is needed to juggle signals around as illistrated, per a bank this will require (in and out) switching of 4 channels between 4 destinations ('filters')

Suggestions on practical solutions here are welcome ...got some ideas already :)

oh, and the led panel is connected upto the CV & Trigger sources to indicate status.. along with audio in and out levels for the 8 i/o chains.. with the assistance of a vu chip per a bunch of leds (signal indiction below their range provided by  plain led)) ...oh and of course indication of which 'filter' is slected needs to be tapped off from the appropriate place.

right thats all for now..

[moxi]

hi Artesia,

i'm working on a MB filter, but let say mine is more simplest...

my first project (i will scan my paper note and post them here, maybe you will find here some inspiration) was more ambitious:

it was just a multimode filter based on cem chip and multimode filter from music from outer space, and using ssm2404 for routing...but price approximation make me go back to a more easier thing (and cause of my poor skill in prog', even if the first project was based on existing MB project: a mb64e that drive a MBCV...)

let me the time to go to the studio then put all of that here...

be carefull when using multiple audio input if you plan to mix the signals, cause some phase problem can appear and that can make your filter sounding bad ,as that appear when working with a lot of input on cheap analog mixer with poor EQ (sorry, I can explain more, i'm just technician, not engineer....)

Are tracking down appropriate parts to make affordable Signal switchers

try the analog device "ssm2404", there are quite simple to implement (just 4 resistor by chip have to be added), and they're are really clickless (here the value of the resistor have to be adjusted depending oon your signal):

I will create another thread to avoid confusion, and just put a link here...

[stryd_one]

Ahh the MBFX project bubbles along. Moogs, Eventides and Sherman QuadFilterBanks are like, so yesterday ;D

rock on guys!

[Artesia]

Hi... Curious Moxi :)

On the mixing and phasing issues.. that will be avoided by two things.. One, in this instance any mixing of resultant signals would be done in the digital domain of a pc.. Two Particular attention would be paid to making sure that other signals in the virtual mix are delayed by the ammount of time that it takes for the resultant signals to come back in the soundcard... A fair bit of software is already capable of soing this by default i beleive (tho i might be mistaken..)

As for using such a thing as a stand alone synth, building excellent filters and then sticking a shoddy mix down on the end would be a crime.. so good circuit design a must for such a module..

[TheAncientOne]

As for using such a thing as a stand alone synth, building excellent filters and then sticking a shoddy mix down on the end would be a crime.. so good circuit design a must for such a module..

Like this one by Marc Bareille?

http://m.bareille.free.fr/index.html

His site is a good source for filters and a few other things too.

I'm not sure when he'll be releasing the mixer, but the good news is that he does PCB's.

Best wishes

Mike

[moxi]

Artesia:

I've created a little web page where you will find the scanned paper notes of my MBfilter project:

http://www.soundandbreakfast.org/divers/MBfilter.html

It's just for inspiration, I'm not sure all is right in this project that I won't continue (I'm now working on something cheaper and less complicate based on analog tool box app...

Other notes I've done (especially for the prog) are too confuse (even for me!) to be published..

but this project is based only on already existing things mixed together, so I'm sure it's possible to do some gear that look like my plans..

Best regards.

[Artesia]

cool.. both very interesting projects... Marc Bareille's widget is curious (i'd buy/build it just to look at ;) ...not quite what im aiming at tho..

Will get back to people on what im doing about this project, and draw up a spec to work from.. Probably going to split things into sections that anyones free to have a go at if they wish too.. ..if its not already been done ..in which case adaptations in places maybe appropriate ...will see.

[moxi]

I forget to say that with my design it's possible to do band-reject filter, using the two 12db filter with linked change of parameter, and bandpass filter , mixing the band-reject filter with the dry signal with phase inversed...but in this case, you're obliged to use the filter in mono mode...I've done some scheme somewhere, I will try to add it to my page as soon as I find it...

[moogah]

Awesome  :)

I'm glad someone is starting work on a project like this, using MB hardware as a means of bridging the gap between classic analog circuits and modern control schemes!

Your idea of embedding a soundcard right into the unit is really cool!  It may prove to be a bit ambitious tho, you'll have a good deal of work to do getting various filters fully CV controlled... something I can prolly help out with  ;)  If you have access to them I would recommend starting this off with a SSM2044 based filter.  They sound good and it will give you time to work out other areas instead of dealing with analog nitty-grittys. 

I've actually got a similar project lined up which is to take the digital brains out of my Oberheim OB-1 and replace it with a slightly modified MBCV to provide full midi control and patch storage, so if you keep posting your progress I will do the same.  Timeline for me is pretty relaxed, I'm busy as hell with work and school so this summer is my goal. 

[Artesia]

heheh.. good one :)

(hmmm.. just changed the thread title to something a little less pedantic)

...iv'e not exactly been known for starting projects ...and finishing them on time ..tho lately been making amens for that.. so you never know. As noted will clearly define and split the project up into units which would be useful as individual projects anyways.. anything involved other people are welcome to have a crack at. ..might actually make it into reality a little quicker if so.

The soundcard wont be built in per se.. itd be unessursarily restrictive to box a nice rackmount soundcard (focusrite saphire pro anyone ?) in the same case...

Mind to save cable hopping, theres no reason that the signal patch bay cant be used to switch the main soundcard i/o's away from the filters to some standard connectors.. to allow further flexabillty.

the oberhiem project sounds sweet :)

First filters in the box are arp2600's and moogs ...the moog one has a resonance pot (from what i recall) ...which will need CV'ing by the way of something like a transconductance opamp. Also if i recall its a pot with a 'weird' lineartity curve ...so the circuit design could get 'interesting' for that..

[kris]

i really like the sound of this project

  would be really amazing to have a 8 channel analogue filter midi controlled in the production loop  id like to help anyway ican but cant promise anything as im not much use at programming but wow keep going .

  kris

[moogah]

First filters in the box are arp2600's and moogs ...the moog one has a resonance pot (from what i recall) ...which will need CV'ing by the way of something like a transconductance opamp. Also if i recall its a pot with a 'weird' lineartity curve ...so the circuit design could get 'interesting' for that..

Eeek.  This is possible, but not a simple matter of subing an OTA for a pot.  I'll look into it sometime this month.  Also, Rob at www.emulatorarchive.com his PCB's for one of the early ARP filters (4072 IIRC.. got one in a drawer here).  Good stuff, same problem in that CVing the rez will be a bit tricky.

[kris]

i like the idea of the filters based on the am3372 as in the matrix synths but then what do i know  im going to start looking for chips i think

[TheAncientOne]

. . . .  Good stuff, . . same problem in that CVing the rez will be a bit tricky.

I tend to the "In case of emergency, fit a vactrol", solution. You might have to do a lot of curve 'linearising', but at least the response speed won't be an issue on the resonance pot, unless you're planning some majorly weird patch.

http://www.pacer.co.uk/product_details.aspx?companyProduct_id=141

Are the UK stockists,  they have a reasonable minimum order cost of £15 plus VAT, and will take telephone orders.

HTH

Mike

[Artesia]

hmm.. you got a point there ..never thought of that ..photoresistor and led is a bloody good idea !

(only question would be over the potential range of resistance available)

[moogah]

OOh! 

Yea, Vactrols are probably a really good idea, the range of values available have a good chance of working on the filters you've mentioned and all you'll have to do is deedle around a bit with resistance values.  As the Prof says their slow reaction time won't be a problem on a rez control, great suggestion!

[Artesia]

yes ..tho diy Vactrols is going to be preferable ...as for a polyphonic moog filter stack ...thats going to be quite a bit of money

[Artesia]

hmm ...also worth giving optoisolators a try ...allbeit ...may only work with a positive or negative bias over 0v ..mind floating application might work regardless ...shall have to try this when i finally get the remaining components for my moog and arp filters.

[moogah]

Found an interesting tidbit last night, Ray Wilson (Music From Outer Space) has PCB's for a SVF and 24db filter both with VC Resonance available :) 

[Artesia]

ooh ! :)

[Artesia]

Current INITIAL panel design... with some further refinements and explaination to come ...have started moddding the case already ..btw this is a smoked perspex bonanza ;)

(Raised front bezel comes forward by 1/2 inch - Case from Scrap Recycled, HP Infered Laser source/psu)

Scematic of internal workings,

eight channels of audio in and out (provided by a maudio 1010lt), filters/cv controllable analog thingys grouped togeather in (8) banks of 4. only one 'filter' selectable per an audio channel, two cvs & hard wired trigger can be used where nessusary (ie when installing a VCO).

An audio/router is needed to juggle signals around as illistrated, per a bank this will require (in and out) switching of 4 channels between 4 destinations ('filters')

Suggestions on practical solutions here are welcome ...got some ideas already :)

oh, and the led panel is connected upto the CV & Trigger sources to indicate status.. along with audio in and out levels for the 8 i/o chains.. with the assistance of a vu chip per a bunch of leds (signal indiction below their range provided by  plain led)) ...oh and of course indication of which 'filter' is slected needs to be tapped off from the appropriate place.

right thats all for now..

[stryd_one]

:o

[moogah]

Wow!  :o :o

[TheAncientOne]

I've been thinking a lot about filter banks recently, and since I'm not a graphics wiz like Artesia, I'll have to describe my thoughts instead.

I imagine a 19" rack cardframe with slots for 8 single filters or 8 pairs, (16), and some kind of routing along the lines Artesia shows. There are some many interesting designs out there, and none are that complex or expensive (until you build a lot!). From the MS20 variants to the Polivox, the Steiner-Parker, Moogs, Ken Stone and Ray Wilsons designs, not to mention things like the wonderfully gnarly wasp, and the CEM variants.

I'd probably try to make pairs, but have them available for normal modular VC work as well. By judicious use of backplane connectors, it should be possible to get the right voltages to the right place, and to electronically lock out/lock down the front panel controls that we want to  remote control, by a suitable signal from the control surface.

The next thought was to tie this in with a variant on the MIDIbox 64e, with 8 pairs of LEDring controls, and some indicator lighted routing buttons. That way, with a bit of bankstick memory, the 64 could act as freqency and in some cases resonance controls for the filter stack, and the more direct control voltages could be mixed in as needed. With the right software on the end, all control input could be recorded - a bit like the way one can 'play the knobs' on Rebirth.

This is definitely a bit too much in one go, but I like the thought of combining the units in this way, and still having them available for other work as needed. Having the Controller on another 19" panel, aligning with the filter bank might be quite good.

A cool option would be to have LCD 'scribble strips' to label the controls, though that might take a bit of working out, even with some cheap LCD's, though at least the LEDrings wouldn't be needed then. A last idea might be to put some I2C EEPROM in the filter modules, like a distributed bankstick, and allow each filter to hold it's own settings, this wouldn't be used in 'stand alone' mode.

A few rather random ideas.....

Best wishes

Mike

[Artesia]

use 40x2 displays as scribble strips ...about the most economical way to the diy'er ...used as seen on the mbseq.

btw on the note of the way this bank unit is layed out ...if another two cv boards where used ...it would be possible to expand the setup to 16 channels of 4 banks ..tho i cant see myself needing that soon.

as for the way the bays work, say for instance i wanted a synth with 8 polyphony on moog filters.. i could fill the first slot in each bank with moog filters ...and the less needed ones ..have as few as desired ..besides for non live use can just over dub as many times as you want to make up for lack of filter duplicity.

I doubt i'll need access to more than 8 filters simaltainiously ...i expect that if it does expand ..itll just be in the direction of more switchable banks ..so itll be 8x8 ..rather than 8x4 ...eventually.

..right back to building the front panel.