Bass pedalboard?

[R.G.]

How much use is a bass pedalboard? An octave of bass notes from, say 41Hz to 82Hz? Foot presses a key, you get that bass note.

How much use is that if it can be set to drone the note until the key is pressed again?

There may be a single-chip solution.

[mremic01]

The thread title makes me think you mean a pedalboard for playing electric bass, but do you mean something like a keyboard that you can play with your feet?

[slacker]

If it could drone I'd definitely be interested, imagine the fun you could have with that and a harmoniser or arpeggiator.

[psychedelicfish]

Something like the foot pedals on an electric organ?

At that kind of frequency polyphony wouldn't be too important, so I guess it could be done using an XR2206 or the like, using the foot pedals to switch a timing resistor. Even better, an arduino could be used, with the pedals switching the various digital inputs to V+. Then you'd have up to 5 analog inputs to control volume and various other things.

It's a cool idea!

[R.G.]

It's actually an offshoot of my thinking about a single-chip electronic Highland bagpipe.

[pappasmurfsharem]

Sort of like a limited moog Taurus pedal.

I for one would love something like this.

I assume your thinking of a noise generator with different pitches?

[deadastronaut]

as a Rush fan...YES PLEASE.

very interested too.

[pappasmurfsharem]

as a Rush fan...YES PLEASE.

very interested too.

My thoughts exactly sir.

[R.G.]

In my copious spare time ( ) I've been pondering top octave generators and bagpipes. Not your usual sort of blue-sky thinking, I realize, but what can I say? My spare time processes run in the background (for all you computer architecture majors out there) and surface occasionally when something related pulls them up.

A fellow with the moniker "old crow" did a top octave generator in a PIC a ways back. It was OK ish, but not great. Years later, thinking about top octaves got me to top note generators, where one chip makes all the octaves of one note, instead of all the notes in one octave. This orthogonal slicing makes programming easier and in some cases possible. And I've always been curious about the idiosyncratic scale of the Great Highland Bagpipes, which are not your normal even tempered scale.

What pulled this together was the need for a single chip tuner reference, a replacement for the onboard LC-tuner in vintage Vox guitars; that was easy enough, but i got asked whether it could be modified to do all of the strings. It could; with a different note constant in the software, it could do any of the even-tempered notes, and probably most of the scales you'd like to do. And give you all the octaves of one note.

This is interesting because a resistor summer on that kind of thing converts multiple octaves of square wave into either a stairstepped sawtooth or triangle wave, which are the fundamentals of old pre-VLSI organ technology. So you can get decent sounding things out of one of these chips, and do formant filtering for voicing.

The final step was when I ran onto a trick to read many switches with one pin of a PIC. This relieved some pin limitations, and let everything fit into one 14 pin DIP plus outboard resistors.

So the PIC looks at a number of switches, nominally 12 in even tempered music, and when no switch is made, mutes the output. When a switch is made, it cross references the switch to a table of "how many times do I have to count my toes before flipping the output bits?" and starts making frequency. It actually makes about six octaves up from the lowest, and then presents all of the bits in those octaves simulataneously on output pins. These pins are then summed to a representation of a sawtooth and can be smoothed, filtered, and amplified.

The hard part, as always, it the mechanics. The last time I was offered a free old electronic organ, I took it; I unbolted the pedal board assembly from it, took the rest to Goodwill, and kept the pedalboard. However, it is possible to make a pedalboard with wood and microswitches. It's also possible to just make a hand board from tactile switches.

Given that there's interest, I'll do a bit more on it.

Oh - limitations. It's strictly monophonic. It will look for and sound the lowest note of any key hit, in common with many organ pedalboards.

[deadastronaut]

''It's also possible to just make a hand board from tactile switches.''

sounds cool to me, i just butchered a sky tv  box, loads of those switches in it...

a friend of mine butchered an old organ and just kept the foot pedals too...he jerry rigged each pedal to the midi controllers  keys..pretty cool through midi as you could have a bass drum, bass notes etc etc..

but a standalone bass drone octave would be nice, just to jam over too.

[amptramp]

Instead of a normal top octave generator, why not try a solid-state Hammond tone wheel?  Use a PLL and dividers to get a 185/196 and 196/185 division ratio and use successive ones of these starting from a 55 Hz oscillator for the A key.  The neat thing about this is if you program a PIC to do a divider, you only need one design for 185/196 and another for 196/185 and you might bea able to fit both functions into the same device so you can daisy-chain the higher and lower notes separately.  Pedalboards don't have that many keys (the one on my old Minshall Model E has 27 pedals), but you don't need that many.  You could just pepper a board with low pin count PICs and maybe outboard CD4046's.

Now here is a diabolical idea: to each PLL, add a narrow-band phase UNlock loop to keep the frequencies slightly off phase lock for true independant tuning to get rid of that phase-locked Thomas organ sound.

[R.G.]

Instead of a normal top octave generator, why not try a solid-state Hammond tone wheel?  Use a PLL and dividers to get a 185/196 and 196/185 division ratio and use successive ones of these starting from a 55 Hz oscillator for the A key.  The neat thing about this is if you program a PIC to do a divider, you only need one design for 185/196 and another for 196/185 and you might bea able to fit both functions into the same device so you can daisy-chain the higher and lower notes separately.  Pedalboards don't have that many keys (the one on my old Minshall Model E has 27 pedals), but you don't need that many.  You could just pepper a board with low pin count PICs and maybe outboard CD4046's.

Now here is a diabolical idea: to each PLL, add a narrow-band phase UNlock loop to keep the frequencies slightly off phase lock for true independant tuning to get rid of that phase-locked Thomas organ sound.

Yep, decent place to do some work.

I was frustrated with the ability to get a single top-octave generator out of a PIC. Accuracy suffers at places where the respective notes have transitions around one instruction cycle time. The solution to that is to use VERY high clock speeds. The idea of slicing the musical note matrix vertically instead of horizontally removed that issue, as you only have to generate one note and a bunch of binary divisions, which is trivial in a uC. Typical organ practice was to generate the full top octave across the top octave, then use many dividers to generate the lower octaves. Generating one note and all octaves from a single IC actually saves an IC - the top octave generator!

I'll look at some math to see if doing a 196/185 output is possible. It may be.

For the other readers: notes are spaced at ratios of the twelfth root of two. This is about 1.059463094..., and 196/185 is 1.059459459...; this is very close, a ratio of 0.999996569 to one another, which is close enough for rock and roll.

It's possible to do a detune in the chip by wiggling the dividers slightly, or using a second chip with a few counts of offset on the dividers to im-perfect-i-cize the output frequencies a bit. I'm pretty sure I can get a "de-tune it a bit" input in there.

One of the aims was to see if I could get it all in one chip. What was lost in doing that was polyphony - more than one note. Bass chords and drones are hardly ever polyphonic, so I thought it was a good trade-off.

I had a couple of hours last night to do some code. It's really funny - the code to do the switch reading is easily three times as long as the code to do the notes. It just goes to show you, the old programming maxim is true: 20% of the code takes 80% of the time; the other 80% of the code takes the other 80% of the time.

[amptramp]

A long time ago, National had a MOS databook (for other readers, this was NMOS and PMOS) that had some PMOS top octave generators in it that had various division ratios.  If you still have that book, you may find the listed division ratios suit your needs.  For monophonic use, you can nudge the oscillator a bit to avoid the lame locked divisor sound.  (But it probably doesn't matter as much on mono.)

Polyphony should be avoided in a pedalboard.  If you hit two adjacent notes, which is easy to do, you may be remembered as the person at the epicentre when the earthquake struck.  If you want to do pedal chords, that may be an interesting exercise in getting one key to play four notes.

You have some choices in switch priority: high note priority, low note priority or latest note priority, to avoid polyphony.  Would it be too diabolical to suggest that you could make that selectable?  If you are satisfied with high or low note priority, there is always a 74148 priority encoder and it can be cascaded.  That takes a bit of effort out of the PIC - it just gets a binary input telling it what divider to take the output from.  You can also poll the switches to make high or low note priority possible just by changing the polling shift direction.  A pedalboard doesn't have a lot of notes - you can afford to be a little more lavish in your chip budget.  You could easily fit enough PICs and CD4046's on a board to make it worthwhile and for mono, dividers from the top octave would be enough.

[amptramp]

I just had another thought: why not use period rather than frequency as your starting point?  This is sometimes used in VHF frequency generators where a PLL would have to be too fast for the technology available but having a high frequency divider with selectable shift reset points may give you as much accuracy as a tone wheel divider with a lot fewer parts - but the parts run at high speed for good resolution.  The old AD9500 digital delay generator (now obsolete) was used that way.  It was only eight bits, but at music frequencies, you can afford lower frequencies and longer divider chains.

[R.G.]

I don't have the MOS databook, but I do have the magic divisor ratios from some work years ago. In making a top octave generator chip, the trick is to come up with divider ratios where the ratios differ by twelfth-root-of-two rather than being twelfth-root-of-two themselves. It gets tricky.

And you're right - period is easier than divider ratio. I'm actually using a period-counting scheme to do division by 1800 to 4500 in one count-down step instead of divider math. It amounts to division by subtraction and counting, but is more suited to large random divisions if hardware divide is not available.

Another challenge is the choice between being fast enough to have some spare cycles every loop and writing isochronous code, which is quite tricky again.

In the one-chip case I'm using, priority is either high-note or low-note, and inflexible once chosen because of the severe restrictions of the key polling method chosen, which was itself a fallout of restricting the number of pins on the chip. The current target is a 14-pin DIP. Some of the 18 and 20 pin parts could scan a key matrix and convert them to logical switch settings then impress any priority you want on it. I did similar software once before and have the code canned somewhere.

Hmmm. I guess it could actually be made random-note priority. The assignment of frequency to key is done in software, and can be anything.

But the priority of which key gets to tell the uC what to do is hard wired, again a consequence of the extreme simplicity of the keyswitch hardware. The keys merely ground various points on a string of resistors. The uC reads one point at the top of the string and gets analog voltages to read. The resistor values are chosen to put the analog voltages in the middle of ranges in the 0-255 bits of an 8-bit conversion, so one A-D read tells the uC the highest (or lowest) key in the string. Other keys may be made but only the highest key voltage is sent to the uC.

I haven't given myself permission to go beyond one chip and passives yet. If the first version on a single chip works well, I may do a fancier version. I had in mind doing a two-chip version to give two low octaves as a first embellishment.

Part of the challenge is to make it dead-simple to make for someone who doesn't have a lot of skills yet, or who is daunted by multi-IC projects.

[amptramp]

Good luck with the project - I would have gone 74HC series CMOS with it because I have found that it is easier to design random logic than to program anything.  Early in my career, I had a job where I had to fix someone else's software.  It was the warning I needed.  Although I was successful, it gave me the aversion to software that remains to this day.  But if you are going into production, the PIC is a small fraction of the cost of random logic, so I understand your situation.

[R.G.]

Not production at all.

There is a huge hump to get over with programming, and for it to be done well, it has to be done with attention to documenting and structuring the code. In my somewhat checkered day job career, I wound up doing programming and eventually managing programmers. I tried to get across to people the importance of "code hygene". It's easy to write dirty code. Dirty code only gets hard when you ever have to touch it again.

Once you get over the hump of writing well documented, well thought out code, it's about as easy as hardware. CMOS logic is easy - until one starts playing tricks with it and using side effects, especially undocumented ones, or depending on the quirks of one manufacturer's products. Then it gets dirty too.

Back when I first took FORTRAN, about 1970, I thought the program statements were the program. It took a few decades to come around to the view that the program exists as a set of operations free of any programming language, very nearly the stuff of thinking itself, and that written-down programs are just more-or-less accurate translations of that set of ideas into one or another language. Accordingly, if the thinking is clear, the translation is easy and straightforward. If the thinking is muddy, no language will help.

[deadastronaut]

this is obviously a much more crude approach..

i used the 74hc14 on my light theremin, i used ldr on one osc, and a pot on another...you can get really nice low drones out of it....and have 6 oscillators per chip

if you used 2 chips you could have an octave....just tune each oscillator...just thinking aloud for really simple drone stuff.

http://www.youtube.com/watch?v=rn16DMoTEPw

heres the info if anyone wants to try it...what a dude..  
http://www.youtube.com/watch?v=fbdWwcEbTwY

as you were...i'll get my coat..

[R.G.]

Got some inspiration on the design. As it sits now, it is one chip, one octave. I made the octave selectable, so it will do the lower four octaves, and that's just because I was lazy about how many octaves to make it do.  So it's morphed into an N-octave generator, one chip per octave. Two-octave pedalboard, two chips. Three octaves, three chips. Still monophonic. Added chaining signals to force higher octaves to mute lower octaves so you don't get one note sounding in each octave if you hit one key per octave.

Alas, there's still a bug in the code. First trial didn't work. Probably a forehead-slapper.

Here's a question - how to build the keyboard? Any clever mechanically-enabled guys got a better idea that
- salvage a pedalboard from a surplus organ
- make an on-guitar keyboard from tactile switches

Actually we need one of each.

[amptramp]

Please tell us what your approach is to the top octave - I love hearing about the various methods of synthesizing a top octave.  Unless, of course, you are doing something proprietary.