# Arduino StrumPad - any builders out there?



## charlieclouser (Aug 12, 2018)

Came across this awesome home-brew project:

https://hackaday.io/project/9465-strumpad

Check out the video, and imagine how great this would be with some of the excellent Kontakt instruments we all have but may struggle to get realistic-sounding parts with.

It's very similar to the old Digitar from CharlieLab (no affiliation!), which I somehow failed to purchase back in the day, and are now very hard to find (and probably break easily).

If anybody out there is an Arduino builder, and wants to whip up a short batch of these, I bet you'd have no problem convincing five or ten of us to buy one - I know I would. I've sent a PM to the builder on hackaday, asking if he'd consider building and selling one / some, and I've included a link to this thread - so maybe he'll show up and chime in.

So, if you're interested, speak up!


----------



## astrocreep (Aug 13, 2018)

That is very cool, thanks for sharing! 

I'm just at the stage of building a simple EQ controller at the moment, so DIY of that might be a while off... 

That said, it'd be great to finally get my hands on something like that which works left handed!


----------



## MatFluor (Aug 13, 2018)

I built my own 4-Fader faderbox - so that could be interesting.

Although the etching of the board could be challenging - and getting it made isn't that cheap


----------



## Olivier1024 (Aug 13, 2018)

Something similar
https://www.tindie.com/products/mid...ord-controller-constructed/?pt=ac_prod_search


----------



## Loïc D (Aug 13, 2018)

MatFluor said:


> I built my own 4-Fader faderbox - so that could be interesting


Can you develop ? It's funny because I'm really thinking building my own faderbox with Arduino in the forthcoming weeks.

@charlieclouser : I'm owning a funny creative device (from a kickstarter project).
It's called Joué by Playful Music (a small french startup in Bordeaux) and can send MPE too.
https://www.play-joue.com/en/

I'm a bit lousy at using it but it's fun.


----------



## MatFluor (Aug 13, 2018)

LowweeK said:


> Can you develop ? It's funny because I'm really thinking building my own faderbox with Arduino in the forthcoming weeks.
> 
> @charlieclouser : I'm owning a funny creative device (from a kickstarter project).
> It's called Joué by Playful Music (a small french startup in Bordeaux) and can send MPE too.
> ...



Yes - I built mine with a Teensy++ (because a standard Arduino doesn't have USB-HID, and I wanted plug and play). I actually thought about marketing it, but the costs of creation are a bit too high, plus there is already the FaderCTRL.

I need to recreate the code to open source it once I have time (new main machine and the source wasn't backupped - silly from me I know)


----------



## Loïc D (Aug 13, 2018)

MatFluor said:


> I actually thought about marketing it, but the costs of creation are a bit too high, plus there is already the FaderCTRL.


No offense but FaderCTRL seems a bit pricey.
After some research it seems that Arduino UNO supports midi over usb but some tweaking is needed.
Leonardo and above can do HID and Teensy architecture seems quite similar.
My plan is to design a flat fader box that I can put on my keyboard and still be able to slide it under my desk.
Pretty challenging. I think 3/4 60mm faders, 2/3 rotary & 4/5 buttons should be enough. No LCD/OLED so far.

If you don't mind, I'd like to see how yours look.


----------



## MatFluor (Aug 13, 2018)

LowweeK said:


> No offense but FaderCTRL seems a bit pricey.
> After some research it seems that Arduino UNO supports midi over usb but some tweaking is needed.
> Leonardo and above can do HID and Teensy architecture seems quite similar.
> My plan is to design a flat fader box that I can put on my keyboard and still be able to slide it under my desk.
> ...



Sure. I made 4x60mm faders on there. wanted to put some knobs, but decided against it


----------



## Mike Greene (Aug 13, 2018)

I hope the builder on hackaday stops by because this looks very cool and it would be great to geek out about it. Hopefully he's planning to sell it, which ends the need for anyone else to try and make something similar.

If not, I have a few thoughts. The first is that this is a complex project, so if someone else tried to do it, then unless they had some major skills, they'd have to radically simplify it.

The onboard processor is doing a lot of heavy lifting which might be beyond the skill of most of us if we tried to do something similar. For example, it looks like this box is receiving MIDI input, then figuring out how to voice the chord for the six strings, as well as some other fanciness. That's a lot of extra coding that involves custom chips that might need to be swapped every time there's a software update. (I could be wrong. This is way above my skillset.)

It might be easier (for a less skilled builder) to make a grossly simplified device that only exports the string_numbers/velocities for each of the six strings (a totally dumb controller), then let the user's computer handle (KSP script, etc) figure out what to do with that note information. That way the device would be simpler to build, plus since it doesn't do anything besides spit out information on which string got "plucked," it would never need updating.

The other thought I have is that I wonder if there's a device that's similar enough that it could be butchered to make a strummer. For instance, maybe there's something cheap with 8 (6 is unlikely) drumpads. I would take the electronics out of the box, then wire those electronics into a new box I build with six "strings," connecting six of the drumpad leads to the "string" leads. That's overly simplistic, of course, but at least it turns a job that's WAY over the heads of almost any of us into a job that might be doable for somebody here.


----------



## chillbot (Aug 13, 2018)

Mike, not to play devil's advocate, but... if all you're talking about is six velocity-sensitive strings that send midi on/off and velocity... I can do that with any six notes on my keyboard. OK it may not be super accurate but I can definitely roll my hands back and forth essentially "strumming" the keys in rhythm in an up-down manner. It's the scripting on the other end that is the super hard part, voicing it like a real guitar on six strings. And the muting or semi-muting of certain strings and hammer-ons and harmonics and geez it goes on and on. But I don't know what I would do with a midi-controller that just let me strum and nothing else... I have 11 of those at the moment that I refer to as keyboards. And let's be honest, if any of use could actually strum well enough for it to make a difference we would just pick up a guitar and plug it in. Hey there's also midi guitars and add-on midi guitar pickups, so what am I missing here?


----------



## charlieclouser (Aug 13, 2018)

chillbot said:


> Mike, not to play devil's advocate, but... if all you're talking about is six velocity-sensitive strings that send midi on/off and velocity... I can do that with any six notes on my keyboard. OK it may not be super accurate but I can definitely roll my hands back and forth essentially "strumming" the keys in rhythm in an up-down manner. It's the scripting on the other end that is the super hard part, voicing it like a real guitar on six strings. And the muting or semi-muting of certain strings and hammer-ons and harmonics and geez it goes on and on. But I don't know what I would do with a midi-controller that just let me strum and nothing else... I have 11 of those at the moment that I refer to as keyboards. And let's be honest, if any of use could actually strum well enough for it to make a difference we would just pick up a guitar and plug it in. Hey there's also midi guitars and add-on midi guitar pickups, so what am I missing here?



Did you watch the video? It takes him zero seconds to get a very realistic rendition of casual / sloppy strumming using only a GarageBand acoustic guitar as a sound source, and the StrumPad is handling all of the spreading of the voices across the octaves, as well as filling in missing "strings" by doubling some notes in other octaves, so you can just hold a triad on the keyboard and brush the StrumPad and get really cool results in real time. There is a piezo sensor in addition to the contact strips which turns the top plate into kind of a microphonic surface, and that is used to derive MIDI velocities for the outgoing notes. One pass, in real time, minimal clean-up of the MIDI performance in the DAW. What he did in the video would be impractical if not impossible to emulate using just a keyboard, and would undoubtedly require beaucoup editing in the DAW to clean it up - for me anyway.

Even though I can "roll" my fingers on the keyboard to approximate a strummed sound, the fact that StrumPad will fill in missing notes means that I don't have to articulate with six fingers across three or more octaves to simulate a six-string guitar - a one-handed three or four voice chord on the keyboard will always result in six outgoing notes if you strum all six of the contact strips. If you only strum three strips, then you'll get three outgoing notes. It's a slick and low-cost solution. I have MIDI guitars but it's not the same - I just want the StrumPad sitting beside a keyboard to add a little life and realism to the many excellent sampled guitar sounds out there.

The StrumPad is very similar to the old Charlie Labs Digitar, which I played with a long time ago and it was a revelation - even with the terrible Roland JV acoustic guitar sound I was triggering with it. I still wish I'd bought one of those back then.

Anyway, I've been in contact with the developer and he's agreed to build me one in a month or so, after he's finished tweaking the piezo sensors and refined the code a bit. I told him about his thread and if he decides to build more than a couple and sell them I imagine he'll stop by at some point.


----------



## Maxime Luft (Aug 13, 2018)

For those who didn't scroll down and couldn't it find it anywhere, like me.


----------



## astrocreep (Aug 13, 2018)

MatFluor said:


> Yes - I built mine with a Teensy++ (because a standard Arduino doesn't have USB-HID, and I wanted plug and play).



Yeah, Teensy seems a better choice as it makes the USB midi part very easy, and the 3.5 is pleasantly small with a lot of digitial pins to play with!


----------



## charlieclouser (Aug 14, 2018)

The drag is that we are so close to having StrumPad functionality in Logic Remote on an iPad - frustratingly close, since the guitar interface in GarageBand does offer a very similar "strumming" mode, but you've got to use the preset chords, and there's no real equivalent for StrumPad's velocity-sensing capability.

It would probably be quicker to program an iPad app from scratch than it would be to build a StrumPad, but I don't have the ability to do either. However, I'm sure that about a week after I take delivery of my StrumPad, an iPad app will appear for $20 that does pretty much the same thing! That's usually how it works - my purchase of some expensive, narrowly focused solution seems to always trigger the release of a cheaper mass-market version. Oh well.

Any iOS developers out there, get on it!


----------



## Loïc D (Aug 14, 2018)

charlieclouser said:


> That's usually how it works - my purchase of some expensive, narrowly focused solution seems to always trigger the release of a cheaper mass-market version.


That's called paving the way...

(coming from a guy who bought a Yahama A5000 sampler right before Kontakt 2 was released)


----------



## Anders Wall (Aug 14, 2018)

charlieclouser said:


> So, if you're interested, speak up!


Yup, did send him/her a message on hackaday linking to this thread.
Best,
Anders


----------



## chillbot (Aug 14, 2018)

charlieclouser said:


> Did you watch the video?


Yup. Didn't mean to go off on a tangent, my response was to Mike Greene suggesting someone could make a real simple version of it, I wasn't quite following. Why I started it with "Mike," sorry if it wasn't clear.


----------



## charlieclouser (Aug 14, 2018)

chillbot said:


> Yup. Didn't mean to go off on a tangent, my response was to Mike Greene suggesting someone could make a real simple version of it, I wasn't quite following. Why I started it with "Mike," sorry if it wasn't clear.



Oh, right. Duh. Sorry. 

Anyway, I chatted with the developer of StrumPad a bit, and he mentioned that he uses a Yamaha EZAG which is like a Digitar bolted to a Starr Labs Z-Tar. It has the short strummable strings of the Digitar and a neck with a matrix of fret buttons. Unfortunately it's been discontinued, but used ones are around $300. The developer mentioned that it would be a trivial matter to create a device (or even a MIDI Scripter plugin maybe?) that uses MIDI input from a guitar controller along with chords played on a keyboard to simulate what he's doing with a keyboard / StrumPad combo. Might be awkward having the guitar in your lap while you try to play chords on a keyboard with your other hand, but... that was an interesting tangent he mentioned.

So that's another possible direction for such a thing. 

I still want a StrumPad though. Simple, dumb, seems to work.


----------



## chillbot (Aug 14, 2018)

charlieclouser said:


> I still want a StrumPad though. Simple, dumb, seems to work.


Mind if I ask what he is charging you for one?


----------



## charlieclouser (Aug 14, 2018)

chillbot said:


> Mind if I ask what he is charging you for one?



So far it looks like it will under $300 - final price to be determined. He still has a bit of work to do on the piezo sensor business that is used to derive "velocity" information. That mechanism may change to something completely different from the 99-cent piezo sensors and the price may have to be adjusted. Could be as low as $200-$250 if the piezos can be made to work the way he wants, more if he has to switch to the force sensors or whatever thing he's trying out. I told him I'd wait until he's got that nailed down. 

There are also a few user options that currently must be decided upon and burned into the unit before he ships it, and can't be edited without an Arduino-flashing rig (whatever that entails) - things like:

- Octave doubling on / off = I think this toggles the "filling in" of missing notes. Let's say you play a three-voice chord on the keyboard, but strum all six "strings" on the StrumPad. With this turned off, only three of the "strings" would generate outgoing notes; with it turned on then all six strings would generate outgoing notes, with the missing ones derived by transposing the keyboard notes up or down by octaves as needed to fill in the missing strings. I think you'd want this turned on all the time, so that even if you played just one E on the keyboard it would be like playing a guitar with all six strings tuned to E. At least, I think this is how that works. Waiting for a full explanation on that one.

- Single or Multi MIDI channel operation = Single channel mode sends all six "strings" on MIDI channel one; Multi channel mode sends channels 1-6. I think you'd want Multi - it's easier to collapse the MIDI channels in the DAW than it would be to expand them, and this would make using a receiving instrument that's in MIDI Mono Mode easier.

- Right or Left handed strumming = I think this determines the order of the "strings". Right handed would make the left-most string play the lowest pitches, while Left handed would be the opposite. I actually think I'd go for Left-handed strumming so that I could play chords on the keyboard with my right hand, since that would be easier - even though it's natural for me to strum with my right hand, I could make it work the other way around, and that would be easier than trying to articulate chords on the keyboard with my left hand.

- MIDI Note Range = This creates a "window" outside of which any notes played on the keyboard are ignored. I actually hope this can basically be disabled, so that any and all input from the keyboard gets received by the StrumPad and turned into something usable - but it may be that there needs to be a limited window to prevent the thing from having a brain fart as it tries to determine what octave to fill in missing notes with or whatever. Not sure what the possibilities and limitations are on this feature.

I'm still waiting for my conversation to continue with him about the exact meaning and limitations of these options, but that's as near as I can guess what they mean at the moment.

Somewhere in his project notes I saw that he mentioned the possibility of allowing user editing of these options from the device itself, but that would require a substantial redesign and addition of a display and buttons to control those options, which would raise the price and complexity substantially - so that probably won't happen. Unless he gets a ton of pre-orders that is! But it's still unclear if dude feels like actually building a bunch of them or if it's just something he'll make one or two of. I'll keep you guys informed as I learn more about his intentions.

Actually it just occurred to me that it might be possible for him to allow changing those user options via incoming MIDI messages such as CC#s or whatever, similar to how you edit the options on a MiniMoog Model-D reissue. Something like, send MIDI CC#99 with a value 0-63 to turn octave doubling off, send value 64-127 to turn it on, etc. It would be a little bit of a pain, but at least you could edit the thing by generating the appropriate CC messages in your DAW, from an iPad, or from the keyboard controller itself. Hassle, but probably cheaper, quicker, and easier than convincing dude to build out a display and buttons etc.


----------



## Kyle Preston (Aug 14, 2018)

Seeing this thread, it's tempting to learn the Swift language & program an app for iPad/iPhone. I doubt it's _that_ difficult a language (it CANNOT be grizzlier than KSP). There's a Brian Eno app that _sort of_ does this with its own internal sounds, but this page would be a good place to start for a hungry developer. I got passed over for a gig due to my lack of Audio Middleware knowledge so I'm hunkering down with FMOD for the next few months... Would love to see someone (braver than I) take a swing at this though.


----------



## chillbot (Aug 14, 2018)

charlieclouser said:


> So far it looks like it will under $300


Yeah I would buy that... maybe let him know if he decides to makes two of them. Personally I think I would go for right-hand strumming and single midi channel operation, but that's all flexible.


----------



## Casey Edwards (Aug 14, 2018)

I highly recommend others to get involved with DIY. It's a lot of fun and with today's availability to YouTube videos learning something new is right at your fingertips! I've built a 16 fader project rather quickly with a Teensy and I'm currently expanding it to work with CV for synths. I hope to have something commercial within a year or less.

The hardest part about these endeavors are finding cases. Trying to find a custom metal shop for our project has proven to be more than extremely frustrating and difficult, so good look with that part! Most pre-fabbed cases just aren't my thing and 3d printing seems like it won't have heft or durability.

I also highly recommend once you're past the breadboard phase that you try and make a PCB for your design. It avoids a rat nest of wires and will keep things nice and tidy.


----------



## Anders Wall (Aug 14, 2018)

chillbot said:


> Yeah I would buy that... maybe let him know if he decides to makes two of them. Personally I think I would go for right-hand strumming and single midi channel operation, but that's all flexible.


I've also spoken to the inventor, I encourage you to send a message saying you're in.
Guessing three (or more) will make it more worth while...
Best,
Anders


----------



## Nick Batzdorf (Aug 14, 2018)

I wonder whether Ilio (US distributor of VSL, Spectrasonics, Gig Performer, others) still has any of these?


----------



## MatFluor (Aug 14, 2018)

I'm sorry, but this image fits this thread like a glove


----------



## charlieclouser (Aug 14, 2018)

Nick Batzdorf said:


> I wonder whether Ilio (US distributor of VSL, Spectrasonics, Gig Performer, others) still has any of these?




Nick, is that your Digitar?!? Or just a photo you dug up?

If it's yours, me so jealous. I call dibs if you ever want to sell it!


----------



## Nick Batzdorf (Aug 14, 2018)

It is mine - I took the photo. I forget why it's been in my closet instead of in my room - it's been a long time.

Will have to try it again.


----------



## pmcrockett (Aug 14, 2018)

The closest mass market device to this that I've seen is the Artiphon Instrument 1, which is an almost-guitar with a touch sensitive fingerboard and a strum sensor that simulates six strings. Dunno if it can be easily rigged to accept keyboard input, though.


----------



## charlieclouser (Aug 14, 2018)

Nick Batzdorf said:


> It is mine - I took the photo. I forget why it's been in my closet instead of in my room - it's been a long time.
> 
> Will have to try it again.



I've had a flurry of email conversations with Miroslaw, the designer of the StrumPad, and we brainstormed some slick refinements to the software side, but he (and I) are really curious about the features and options of the Digitar. Any chance you could photograph or scan the manual and upload or PM it to me? I've only messed with one about a decade or two ago and I can't remember anything about it other than I thought it was cool as heck, and I promised myself I'd buy one but somehow I forgot..... until now.

Did you ever see the Charlie Lab keyboard with integrated Digitar? How did I not buy one of these? It has my name right on it!


----------



## Saxer (Aug 14, 2018)

Just found this buried under a bunch of cables... didn't use it for years (royal dust collector). I'm not a guitar player so it doesn't really help if it doesn't groove when you move. I used it for some arpeggios here and there but I'm much faster editing Midi for such kind of stuff in Logic.
Don't know if it still works but it was stored dry and warm and untouched. No cable and no manual but I think the connection cable between the device and the Midi box is a standard network cable?

@*https://vi-control.net/community/threads/arduino-strumpad-any-builders-out-there.74053/members/charlieclouser.3876/ (charlieclouser) *interested?


----------



## charlieclouser (Aug 14, 2018)

Saxer said:


> Just found this buried under a bunch of cables... didn't use it for years (royal dust collector). I'm not a guitar player so it doesn't really help if it doesn't groove when you move. I used it for some arpeggios here and there but I'm much faster editing Midi for such kind of stuff in Logic.
> Don't know if it still works but it was stored dry and warm and untouched. I think the connection cable between the device and the Midi box is a standard network cable?
> 
> @*https://vi-control.net/community/threads/arduino-strumpad-any-builders-out-there.74053/members/charlieclouser.3876/ (charlieclouser) *interested?



Oh hell yes. Even if it's only for research purposes. I love weird-o stuff like that. Where you at? How much you want for it? PM me and let's make a deal!


----------



## MartinH. (Aug 15, 2018)

Kyle Preston said:


> Seeing this thread, it's tempting to learn the Swift language & program an app for iPad/iPhone. I doubt it's _that_ difficult a language (it CANNOT be grizzlier than KSP). There's a Brian Eno app that _sort of_ does this with its own internal sounds, but this page would be a good place to start for a hungry developer. I got passed over for a gig due to my lack of Audio Middleware knowledge so I'm hunkering down with FMOD for the next few months... Would love to see someone (braver than I) take a swing at this though.



I don't know how hard swift is, but Objective-C wasn't too bad, and if you know C#, you could use the "Unity" game engine to develop for iOS. You'd have to learn different APIs and paradigms for how to do UI stuff etc., but you would get the advantage to easily be able to also deploy the app to other plattforms like android.
I don't have an iPad, but afaik there are these pressure sensitive pens for drawing as input devices, that could be used for inputting velocity of notes.


----------



## wst3 (Aug 15, 2018)

couple observations from a former hardware designer...

The software is still the key for a device like this. And as Charlie points out, once you have the hardware and basic operation in place you (or the programmer of your choice) can extend the capabilities almost without limit. The only limit is the hardware.

The DIY site provides links to what appears to be all the software, and a schematic, and even PCB layouts (wish they were gerber files, but you can't have everything!)

Based on the schematic this is one of the simplest projects I've run across, and even a novice could build this in an evening.

No such thing as a free lunch - I suspect getting the capacitive sensor part right will be a little tricky. Most board houses that do prototypes will offer "do-overs" at a very reasonable price. After the first one of course.

And there's the rub - the cost of a single PCB will be significantly higher than the cost if several are purchased. Single run PCBs are expensive, even from the "discount" houses. I do not think you will see a meaningful break on the cost of the parts until you hit a much higher number, so the savings will come from getting enough PCBs ordered.

It's probably no more than a half a days work to translate the PDF of the layout into a CAD package that can output the necessary files, so you don't need a ton of orders to cover that.

Seems to me this is a very do-able project for the group, but it would require quite a few people showing interest (e.g. paying a deposit) to bring the cost down.


----------



## chillbot (Aug 15, 2018)

Sprechen sie Deutsch?


----------



## MatFluor (Aug 15, 2018)

chillbot said:


> Sprechen sie Deutsch?



Do you need sections translated? Or anybody else for that matter?

Native German speaker here


----------



## Mike Greene (Aug 15, 2018)

chillbot said:


> Mike, not to play devil's advocate, but... if all you're talking about is six velocity-sensitive strings that send midi on/off and velocity... I can do that with any six notes on my keyboard. OK it may not be super accurate but I can definitely roll my hands back and forth essentially "strumming" the keys in rhythm in an up-down manner. It's the scripting on the other end that is the super hard part, voicing it like a real guitar on six strings. And the muting or semi-muting of certain strings and hammer-ons and harmonics and geez it goes on and on. But I don't know what I would do with a midi-controller that just let me strum and nothing else... I have 11 of those at the moment that I refer to as keyboards. And let's be honest, if any of use could actually strum well enough for it to make a difference we would just pick up a guitar and plug it in. Hey there's also midi guitars and add-on midi guitar pickups, so what am I missing here?


The appeal (to me, at least) of a separate controller is that you can brush your finger(s) across the "strings" and the timing of the MIDI notes will be authentic. Even someone who isn't a guitar player would be able to do a basic 1/8 note up/down strums for a rock/pop song, or a slow strum for a pretty song ending. It also wouldn't take long for a non guitar player to discover they can strum just the high (or low) strings for some of the strums, which will add more variety/authenticity to the pattern. Granted, that can be done with a keyboard by moving/deleting notes, but this is better.

Also, this device is set up so you don't need to know chord fingerings or anything like that. The chords are set by the keyboard controller, so you hold an E chord on that keyboard controller and the software figures out what fret/note each string on the Stringpad should be assigned to. (Shameless plug - just like RealiBanjo or https://realitone.com/fingerpick/ (Fingerpick).)

One other thought - I'm a decent guitar player myself, but for a lot of work, using a plug is preferable to using a real guitar. For starters, tuning is always an issue with real guitars, which makes it take longer. Even if the guitar is in tune, once you start playing further up the neck, it's easy to be out of tune on one string if your finger is pushing a little too hard/soft. Over the years, I've probably done thousands of re-takes because of tuning.

Also, MIDI has the advantage that you can try lots of guitar quickly. For acoustics, that's especially relevant because they sound so different. Plus with acoustics, you have to set up a mic, which for a lazy guy like me ... ugh. And you can tweak performances more quickly with MIDI.


----------



## Saxer (Aug 15, 2018)

Mike Greene said:


> Over the years, I've probably done thousands of re-takes because of tuning.


I could save a detuned rhythm guitar recording recently by using the polyphonic algoritm of Melodyne. Great time saver!


----------



## burp182 (Aug 15, 2018)

This is kind of a flyer, but I wonder if there's a way to adapt a Suzuki Omnichord for this use? Years ago I sold 3 of them to Dolly Parton (she loved them because they'd still work with her acrylic nails) and I hadn't thought about them in ages. But I seem to remember a version with Midi out and it did what the StrumPad appears to do, with the addition of chord selection. (It works kind of like a zither.)

Just wondering...


----------



## MartinH. (Aug 15, 2018)

As cool as I think all the custom DIY hardware stuff is, I still love efficiency slightly more and I feel I have to ask: why does it have to be this custom PCB hardware solution that might cost 200$+, when you theoretically could just buy a ~70$ android smartphone and just use the touch display of it with some custom built software? It would be much more versatile because you could put other optional functions like faders etc. in there as well. And you have more dimensions of data that you can input. E.g. you could use two-fingered swipes where the distance between the fingers controls the velocity of the strummed midi notes. And if you need some kind of haptics, you could try cutting strips of display protection foil and put them on the display where the touch zones for the individual strings are. 
Just a thought... of course custom hardware is cooler and has more "wow factor" and possibly also better durability.


----------



## wst3 (Aug 15, 2018)

The touch screen on a phone is a pretty flexible device, but it still can't do everything that a custom hardware interface can do.

For some that is a benefit, for others, maybe not.


----------



## charlieclouser (Aug 15, 2018)

MatFluor said:


> Do you need sections translated? Or anybody else for that matter?
> 
> Native German speaker here



I was about to say, "yes, please translate" but the StrumPad developer send me a link to a Google Translated version, which I will upload here. But thanks anyway for the kind offer!


----------



## charlieclouser (Aug 15, 2018)

wst3 said:


> The touch screen on a phone is a pretty flexible device, but it still can't do everything that a custom hardware interface can do.
> 
> For some that is a benefit, for others, maybe not.



Yes, it seems that a big issue in using a smartphone / tablet for music creation is velocity sensitivity, and how to simulate it. Some EuroRack modules have FSR or capacitive touch panels to generate control voltages, and these are very sensitive and great to operate, but apparently this isn't possible with current smartphone and tablets - and I'm not clear if it's a limitation of the hardware or just the operating system and how the OS polls the surface. Some of those EuroRack modules are not actually sensing pressure per se; they appear to derive a pressure value by measuring the area that the fingertip covers on the surface - the harder you press down, the more you fingertip "squishes" and the more area it covers. 

Pretty ingenious.

At one point I thought there was an MPC-style drum machine on iPad that was simulating velocity sensitivity with a similar method - like if you hit harder your finger will squash more on impact - but others have told me that the iPad (or iOS) can't actually measure the area occupied by a single touch, only derive a center point for each touch - so i may be mis-remembering that part. Not sure how accurate that info is, and whether this can be changed with an OS update or would require different hardware behind the touch sensing system. Either way, I hold out hope.

But the way in which StrumPad solves that problem, with a 99-cent piezo sensor, is ingenious and seems to work well. Indeed, the casual manner in which the StrumPad is played in the demo video, and the ease with which "sloppy" results can be achieved, were exactly what piqued my interest. It's not that I "need" a strummable guitar controller, but interesting and innovative solutions always make me prick up my ears. So I'll get one - and I might finally be able to use all of those 20-gigabyte ukulele libraries I bought on black friday!


----------



## MartinH. (Aug 16, 2018)

charlieclouser said:


> Yes, it seems that a big issue in using a smartphone / tablet for music creation is velocity sensitivity, and how to simulate it. Some EuroRack modules have FSR or capacitive touch panels to generate control voltages, and these are very sensitive and great to operate, but apparently this isn't possible with current smartphone and tablets - and I'm not clear if it's a limitation of the hardware or just the operating system and how the OS polls the surface. Some of those EuroRack modules are not actually sensing pressure per se; they appear to derive a pressure value by measuring the area that the fingertip covers on the surface - the harder you press down, the more you fingertip "squishes" and the more area it covers.
> 
> Pretty ingenious.





charlieclouser said:


> At one point I thought there was an MPC-style drum machine on iPad that was simulating velocity sensitivity with a similar method - like if you hit harder your finger will squash more on impact - but others have told me that the iPad (or iOS) can't actually measure the area occupied by a single touch, only derive a center point for each touch - so i may be mis-remembering that part. Not sure how accurate that info is, and whether this can be changed with an OS update or would require different hardware behind the touch sensing system. Either way, I hold out hope.



I stopped actively doing iOS development many many years ago, but back then, the info for surface area covered per touch point was available as an undocumented low-level api function, so something that the hardware can do, but you wouldn't be able to actually release an app using it on the appstore, because using the undocumented api functions wasn't allowed. What that tells me is that it might be possible on android, but I don't know for sure. 

What I did when I prototyped a painting app on a first gen iPad, was poll data from the accellerometers and use that. If you press harder you are usually also moving the device more as you swipe (doesn't work if it's on a super stable mount, strapped to your midi keyboard). I believe this technique is also how Garageband on my old iPad simulates velocity sensitivity on the drumpads. 

If you use a touch display you could also use the y axis position to input velocity, if the x axis is the strumming direction. So instead of doing a different sound if you strum closer to the "bridge" of your virtual guitar, it would just be quieter. 

I really don't want to talk you out of the hardware solution, I'm just sharing what little knowledge I have and hope it might be useful for someone, possibly on another project.


When I was younger I wanted to have a Boss HM2 pedal because I was chasing the oldschool swedish death metal sound like the holy grail. So I downloaded the schematics from some site, ordered the parts, and tried to solder one together... I must have done something wrong or ordered the wrong parts, it didn't work and I lacked the skill to fix it. In the end I just bought one used off Amazon, and later Behringer released a clone of the pedal. Also I found out that the pedal alone gets me nowhere near that sound .


----------



## pmcrockett (Aug 16, 2018)

If you're going the DIY iPad route, another possibility would be to use a graphics tablet instead, which would give you pressure sensitivity. I've managed to capture and process graphics tablet input to produce MIDI output with Pure Data, and I think Wacom has an actual API available for their stuff if you want to do it properly.


----------



## charlieclouser (Aug 16, 2018)

MartinH. said:


> If you use a touch display you could also use the y axis position to input velocity, if the x axis is the strumming direction. So instead of doing a different sound if you strum closer to the "bridge" of your virtual guitar, it would just be quieter.



Hey, that's a good solution for sure. That would totally work.

In my situation I'll probably be playing the chords with my right hand and "strumming" with my left hand - even though it's a little ass-backwards as I play guitar right-handed, my left hand is crap on the keyboard - and since my left hand is probably also crap at strumming, doing it your way would probably be easier for me to control than trying to get accurate velocities from striking the StrumPad with consistent force.

I also wonder if a MIDI Scripter plugin in Logic could be made that would let you use the touch-strip on things like Dave Smith synths or those NI Kontrol S-88 keyboards as a sort of strum pad. Obviously the velocity sensitivity thing would be out of the question, but maybe aftertouch could be used for that. 

The Script would need to sample the touch-strip position, while capturing and blocking keyboard note input, transposing the keyboard notes to the appropriate octave for each "string", then releasing the notes for each "string" as the touch-strip value passed each of six equally-spaced points - while using aftertouch (or foot controller) to generate the velocity values for the note events as they are sent. If you had a keyboard with poly aftertouch it would be even more expressive. Since the touch-strip is basically a mod wheel, you could also strum from a mod wheel on any keyboard - although this would probably be a little more awkward than a touch-strip.

I know I'm putting way too much thought into this, especially as I don't really use strumming type of sounds, but I just like exploring the possibilities. 

I also realized that my Linnstrument already has a "strum" mode. Now where did I put that thing?


----------



## MartinH. (Aug 16, 2018)

charlieclouser said:


> I know I'm putting way too much thought into this, especially as I don't really use strumming type of sounds, but I just like exploring the possibilities.



I can relate, these clearly defined creative tech problems are compelling to solve. Earlier today I was contemplating whether I should try to use a software-side programmable keyboard for triggering autohotkey scripts, or search for an arduino based hardware usb-key-remapper that I can use with any type of usb numpad or keyboard.


----------

