reinventor

Archive for July, 2011|Monthly archive page

Guitar reInvention

In Uncategorized on July 25, 2011 at 8:03 pm

I’d like to share another reInvention created by myself and my buddy Are.  We imagineered this thing from scratch, built and tested it working properly on a real guitar, then of course discovered patents on the basic concept going all the way back to the 1930’s!  So it was one of the original ideas for an electric guitar pickup, but it was ahead of it’s time.

It took until the end of 2008 for us to reinvent it, and by then technology had evolved to the point that it became practical.  So practical in fact that I have the guitar in working condition sitting next to me right now as i type.  Although I say that the concept originated in the 1930’s – and also there were many other designs proposed over the decades – we put a little design twist on it that made it practical for use on modern guitars and other stringed instruments.

So enough about the origins of this reInvention, let’s talk about how it works.  It all starts when we put strong neodymium supermagnets in an alternating pattern under the strings.  I cut up a cookie tin to make thin little plates which i secured to the surface of the pick guard with double sided foam tape, right underneath the strings.  Then I stuck magnets under the strings.  See the photo below for a close-up of this arrangement.

Those are 9mm square magnets and the strings are 10mm apart, so the fit is close enough.  Note that the strips of magnets are snapped together as they run across the strings because the magnets are alternated like this:  NSNSNS.  That way the magnetic fields add up beneath each string instead of fighting with each other.  This is one of the keys to making this pickup system work.

What happens when you strum the guitar strings is that they vibrate perpendicularly to the magnetic field that they are located within.  According to physics, this creates a tiny electrical current that flows along the length of the wires.  These currents travel to the headstock where they end up at the tuning pegs and there they need a place to go so that we can collect them, boost them, and send them out to the guitar amp.  That’s where the following photo gets important.

Here I have shorted the tuning pegs together with lugs that were laboriously fastened out of tuna can lids with a Dremel tool, which tool forever and a half!  Once the lugs were created and soldered together carefully they formed a shorting block that electrically sums all six string currents together into a single combined current.

“Ah,” you say, “but how do you get that current back down the neck where it can be boosted and sent out the guitar jack?”  The simple answer is you use the truss rod inside the guitar neck as the return conductor.  That part is actually one of the main contributions to the state of the art that Are and I made.  Prior art in the patent record typically required an insulated bridge which is not standard equipment on guitars, so it is not manufacturable easily.  Our approach maintains the bridge at ground potential so no changes are necessary to the bridge.

So anyway, our tiny little electromagnetically generated currents have now gone full circle from under the strings, up the neck, down the neck, and back into the guitar body.  At this point we could just send the signal out to the guitar jack and put a gain pedal between the guitar and the amp to get our signal.  However that means super tiny currents traveling in the guitar cable which leads to noise issues.  So the solution is to boost the signal inside the guitar.

In our prototype we used a special microphone transformer with a mu-metal enclosure to accomplish the signal boosting.  The result is a signal strength about half as strong as a conventional pickup produces which is close enough for our purposes.  However we have since realized that an opamp gain circuit or similar would be the ideal choice here.

That means putting a battery in the guitar or otherwise delivering power to the guitar through the guitar cable or via solar cells with storage capacitors for playing in dark environments or other such complications.  This turns out to be worth the effort for the improvement in audio quality.

So how does it sound?  Clean, in the sense that it sounds like an acoustic guitar.  In tests with guitar players, I found that pretty much none of them like this sound, haha.  They are accustomed to the distortions created by the second order low pass filter that exists in conventional wound pickups and they don’t like the clean sound.  I tried many times to explain to them that we could introduce the characteristics that they preferred with additional circuitry and even make that adjustable without having to swap out pickups, but got zero positive response.  Not one guitar player likes this pickup system.

However, I feel that it’s great for certain styles of guitar play such as bluegrass or classical where the acoustic sound is preferred.  Also it would be useful for making an electric violin that was true to the violin sound instead of distoring it like conventional pickups.  It’s also great for any metal stringed instrument including custom instruments that people build for academic, industry, or hobby purposes.  So the guitarists do not have the final say after all.

One last thing I’ll mention is that this system should also be nice for hexaphonic guitar output where you capture all six string vibrations separately and send them out on a multiconductor cable to the amplifying equipment. That can be accomplished by not using the shorting lugs and simply sending six return wires down the neck in a separately machined channel in the neck.

So there you have it, from the 1930’s to today, about 80 years later an idea gets reinvented and made practical by the advancement of technology a a couple of hobbyist fiddling around.  Another reinvention bites the dust, so to speak.  Well, i should stay positive – perhaps some one will find this reinvention useful and actually tell me about it.  Enjoy your day.

Boolean Sequencer Basics

In Uncategorized on July 25, 2011 at 3:27 pm

There are many kinds of sequencers in the world of music creation, each with their own unique set of characteristics.  When I started creating music, however, I knew nothing at all about them not even what a sequencer was.  I could make lots of sounds with ChucK programs and make random notes and such, but I didn’t even know what the word sequencer meant.  All I knew was I wanted to make songs from these sounds.

To this day four years later I still have a limited understanding of all the fascinating variety of sequencers out there but there is one that I know very well:  the Boolean Sequencer.  That’s the name I chose for a technique that I later realized is as old as synthesizers themselves, maybe older.  Possibly a great deal older, historically, but let’s stick to modern day electronics versions.

So not knowing what to do, I got creative.  I remembered Boolean algebra and truth tables and Karnaugh maps and all that jazz from college, and I also remembered programming FPGAs with the Verilog language.  I imagined that there might be some way to take a logic truth table and step through it with a counter, producing a series of on and off signals.  This could tell me when to play notes.

I tried it and it worked, yay \o/ I was making songs – sorta kinda.  But these were one note songs but they had interesting rhythms, patterns of notes that caught my attention.  I was on to something good it seemed.  Then I wondered:  what if that series of ones and zeroes was actually a series of note frequencies?  How could I generate that?

Well long story short, I ended up with a very simple combined digital and analog architecture that I named the Boolean Sequencer, comically producing the acronym BS as a coincidental joke.  That thing is pure BS, I laughed about it!  Well the only real BS was that I thought I was inventing something when I was actually reinventing it, more on that later.

The architecture ended up as follows:  Tempo clock to binary counter to logic network to aggregation network, and out pops a Control Voltage (CV) that can be applied to any music making circuit that responds to an input voltage.  I played around with this BS thingie and learned a lot about it and I will share some of those findings with you shortly, but first let’s examine the stages:

The tempo clock is just an oscillator that produces a digital output.  If you want six notes per second you set the tempo clock frequency to 12 Hz.  Why 12 Hz instead of 6 Hz?  Because the clock will be fed into a binary counter which will divide it by two with the LSB flip flop.  Alternatively if you actually use the clock itself as the LSB you can make it be 6Hz for 6 notes per second timing.

The counter is usually one of the binary counters CD4020, CD4040, or CD4060.  These all count out a binary sequence and make most or all of the bits available on the output pins.  So we clock this counter and this produces a binary count N bits wide.

Next up we have the logic network which accepts the counter output bits as input.  It may be any logic function of the available bits from the counter, and may be any number of bits wide at it’s output.

Finally there is the aggregation network which is often just a set of resistors connected to the logic outputs such as a multiple input voltage divider or an R2R ladder.  I call it an aggregation network because it can be very aggravating!  Just joking!  Actually it aggregates the digital outputs into an analog signal, the CV.

Got all that?  Now let’s discuss some of the properties of Boolean Sequencers.  One is that they can have any sequence length that you like but normally you just set them for a binary whole number of steps like 8 or 256 or 65536 or whatever.  65536 steps?  Holy synthesizers Batman, that’s a lot of steps for a sequencer to have before repeating!  Yep, due to how quickly the power of 2 grows as you add bits, you can get amazingly long sequences.

And those sequences will be completely unpredictable!  Well actually they are very predictable according to boolean algebra and analog circuit theory, but the tendency is not to design for a specific sequence but rather tho just haphazardly hook up logic and aggregation networks until you like what you hear.  You can create by design or by exploration, that’s up to you.

I can say this, however:  AND and NOR gates tend to create sequences with gaps of silence especially at the beginning of the song and get far more active later in the song.  It’s the opposite for NAND and NOR gates, and XOR and XNOR gates tend to be active all the time, with no gaps at all or very few.

One last note about the characteristics of a BS is that it generates fascinating patterns within patterns within patterns.  Just stare at the counter part of the logic netowrk’s truth table (the binary count part) and your eyes will glaze over as you see all these fractal patterns nested at every level of hierarchy.

Well, the same is true of the logic output only in a more entertaining way.  As you listen to the song your mind will latch onto a phrase (pattern) and then hear it again a few times perhaps then again but a little bit different twice, then back to the first one just once, then another new one, and so it goes throughout the song.

I’ll finish up where I started and just mention that the Boolean Sequencer is not really a completely original idea.  In fact it has been created many times before as I have noticed diode arrays in step sequencers and other circuits that effectively implement a BS, and also I have heard what sounds like familiar old tunes in some of the BS programs that I have written.

In fact, I wouldn’t be surprised if the Boolean Sequencer was known well before electronic synthesizers even existed, maybe even centuries old dating back to ancient culture in woven patterns, celtic knots, or tiled art – who knows where binary combinations originally exited?  But that part is strictly conjecture.

Thank you for reading about all this BS stuff, heh, and I hope you enjoy listening to some Boolean Sequenced music or even make some of your own.

 

Percussion Karplus Strong Inspired

In Uncategorized on July 25, 2011 at 11:52 am

Ka-tish Ka-tish Ka-tish go the synthesized drums as part of your eChuck music circuit.  How did you do that with a NAND gate?  Why, you used the percussion circuit shown above – easy!

*** Edit:  Please note that this circuit works with the HEF4011EP surplus NAND chip, and not with the CD4011BCN new chips.  We found that out the hard way when some readers could duplicate the circuit easily and others could not at all.  You can purchase the HEF4011EP chips from Electronics Goldmine, or at least that’s where I got my chips.  This is an occasional issue with linear CMOS and I wish I had been enough of a perfectionist to see it ahead of time, but at least we know now.  ***

Here’s how I dreamed it up myself, though I’d be surprised if it was not an already discovered circuit (remember the “re” in “reInventor”).  Nothing new under the sun as they say, right?  Well I was working on a circuit design for the Lunetta Challenge at http://www.electro-music.com and I wanted something fun and uniqe for the next subcircuit.  So as I lay down to sleep I imagineered the above circuit as a super simple linear CMOS version of the famous Karplus Strong algorithm.

The what?  The Karplus Strong algorithm, first published in 1983 by professors Karplus and Strong, it is a simple algorithm involving a summing amp, a delay line, and a filter in a feedback loop.  You apply a burst signal such as a pulse or a burst of noise or somesuch to the summing amp and the circuit’s feedback loop rings out percussive or stringed instrument types of sounds.

I had worked with Karplus Strong for years and even sold a bunch of modular synthesizer boards to electro-music friends, so I had become quite familiar with it.  Well, I reasoned, if the NAND gate was behaving like linear CMOS then it could be like the summing amp.  Then for the delay and filter I used an RC feedback circuit to one input, and added an inverting opamp type circuit with feedback and input resistors to the other input for the gain control of the summing amp.

The whole thing was all smooshed together around one NAND gate, and I had no idea if it would work anything like a Karplus Strong loop, but I was willing to give it a try.  This is an example of the creativity process that I hope you enjoy designing with as well.  Take some ideas, sort of squeeze them together into a simplified version of a thingamajig and try it!  You can’t be afraid to fail when it comes to reInventing the wheel.

So anyway I didn’t have a noise burst or even a pulse, just a square wave, so I added an input capacitor to give me edge pulses at the input from the square wave.  I fired it up and gently adjusted the volume pot – tada!  Percussion emerged from my weird little circuit.

It was chirpy Ka-tish sounding synthesized percussion, and certainly not the very best kind of synthesized percussion, but lo and behold it was indeed percussion from a single NAND gate and a few passive components.  Well I wanted something a bit more interesting than just the same sound repeated over and over so I mangled up the input with an extra resistor so that two digital signals were mixing at the input and I ended up with a nice little percussion rhythm.

OK, sold you on this circuit?  You wanna build it?  Yes!  Of course you do, so I’d better tell you the values of the components.  Start with 100k resistors in all three places and 0.1uF capacitors in both places.  Then try doubling or halving the various components to see what kind of sounds you get.  Go to a wider range of values for even more variation.  Also I suggest using a 100k pot in all three resistor positions for full experimental adjustability.

I’m not giving you exact values for the circuit I ended up with because the input is more complex than the circuit shown and also I can’t see all of the color codes with these 44 year old eyes, lol.  Also my meter broke and I haven’t made it a priority to get a new one so I cannot easily measure the components that I used.  Plus I’m lazy like a lot of creative people, heh.  Well I do get industrious from time to time but not today.

Which, as a side note, I’d like to mention that these little eChucK / Lunetta circuits are so simple that you don’t even need to use test equipment other than amplified speakers to listen to the signals – if you know what you are doing that is.  By all means use all the gear you have if you do have it, I do not.  Designing music circuits blindfolded?  As Richord Pryor joked in the movie Stir Crazy, “That’s right we bad, that’s right we bad!”

LOL, just kidding!  As the legendary Jimi Hendrix said “Dont’ get mad nawawww…”  OK enough silly ramling, off you go – build your own homemade percussion circuit right now!  Go for it!

eChucK Spatializer Circuit

In eChucK, Music on July 25, 2011 at 6:33 am

An eChucK Lunetta Spatializer Circuit

We’ve all heard the sound effect of music wooshing from one side to the other, especially while listening with headphones.  Ever wonder how that’s done?  It’s easy:  just make the left channel signal amplitude reduce while the right increases.

Actually good spatialization as they call it requires a lot more fancy stuff that models the speed of sound in air as it travels from the sound source to your ears in two separate and unequal paths, but you can get pretty good results from just fading the signal amplitudes.  That’s what this circuit does.

I created this eChucK Spatializer circuit in software form first by programming it in ChucK, then imgineered it into hardware form using a 4000 series CMOS analog mux chip, the CD4052.  It provides four spatial positions:  left, left of center, right of center, and right.

What you do is you apply your music signal to the input buffer, then select the spatial position with the A and B input pins to control where the sound will appear to be.  It works by creating four voltages with a voltage divider made of three resistors, then multiplexing those voltages to the left and right channels.

The voltage divider provides voltages Vin, (2/3)*Vin, (1/3)*Vin, and 0*Vin.  We apply these four voltages to the four X channel inputs, then apply them in reverse to the Y channel inputs.  The result is output voltage pairs of (left, right) equal to (1, 0) or (2/3, 1/3) or (1/3, 2/3), or (0, 1) times Vin, thus crudely but effectively spatializing the monaural input signal on the stereo output channel.

If all those numbers just went wooshing over your head like a jet airplane, just think of it this way:  the digital control input selects the appropriate left and right channel signal levels to create the impression that the sound source exists at one of four places.  Changing the digital input value moves the perceived location of the sound to a new position each time.  So you connect time varying digital signals to the A and B inputs and you get sound bounding around inside your head (with headphones) or in front of you (with speakers).

To create that left-to-right motion effect, just put a two bit binary count into the inputs B and A, with B as the most significant bit and A as the least significant bit.  That way the left channel amplitude reduces while the right channel amplitude increases.  The sound will be stepped in four positions instead of smoothly changing, but hey what level of perfection do you expect from a humble logic chip?  Not a bad effort for the lowly mux, I’d say.  Well done little CMOS chip, you’ve earned soome well deserved electrons!   Now go forth and spatialize your audio.

 

eChucK Overview

In Uncategorized on July 25, 2011 at 4:39 am

You may be wondering:  “What the ChucK is eChucK?” and rightfully so.  eChucK is electronic ChucK, a hardware implementation of a music programming language modeled after modular synthesizers.  Now say that ten times fast!  Haha, in simpler terms eChucK makes music.

The way that eChucK makes music is we create very simple circuits and wire them together into a musical electronic system.  Each of the simple circuits is a distilled down basic version of a fancy expensive modular synthesizer module.

For example, we might use a 555 time oscillator to create a square wave clock signal on one little eChucK board, send that into a CD4017 based Baby10 step sequencer, and then drive a 40106 voltage controlled oscillator to create our music signal.  Send that into a pair of powered computer speakers and you’ve got yourself a simple little music maker for a barebones price (or free if you scrounge for parts).

So what about this ChucK music programming language?  Well, eChucK was imagined by a ChucK programmer, namely me, as a way of implementing the software pieces that bolt together to make music in hardware form.

The history here is that in the 1960’s the modular synthesizer was invented and existed as huge electronic monstrosities full of tubes and transistors and such.  Each modular synthesizer consisted of many modules that fit together into a rack, forming a monolith of music.  Patch cables wired all the modules together and the whole thing looked like an old timey telephone switch operator’s panel, basically a tangle of cables on a panel.  Once you wired it up you adjusted knobs and switches on the panels to make different sounds.

Fast forward to recent years and a young music grad student named Ge Wang gets the idea to model these modular synthesizers as well as other musical instruments in software form.  The famous quote from his professor was:  “Go for it!” and ChucK was born.  Today ChucK continues to evolve into more and more powerful forms as new versions are released from time to time.

We now bring you to October of 2007 and I am browsing through the downloads page of the Apple computer web site (don’t worry, ChucK is cross-platform to Mac, Linux, and PC), and what do i behold?  Why it’s ChucK of course!  Amazed that such a thing exists as a programming language that creates music, I quickly download it and give it a try.  Suddenly I am a ChucKist and begin to code away with glee.

Then I notice on the ChucK website that there is a forum for ChucK on http://www.electro-music.com!  Oh joy, i can share my excitement with others.  Well, long story short my background in programming and electronics gets me thinking and talking and pretty soon I envision an electronic version of ChucK:  eChucK.

So we’ve come around full circle from electronics to software and back to electronics, only now it’s 50 years later and electronics have gotten a whole lot smaller and cheaper.  So small and so cheap, in fact, that we can make little simplified versions of the bulky 1960’s modules on circuit boards the size of a large postage stamp.  Things now become not just smaller but easier, cheaper, and a whole lot more fun for the average person who could never afford to get their hands on the old monoliths.

Well that’s my story and I’m sticking to it as the song says.  Now you have a better idea of what eChucK is all about and how it came to be.  In another blog entry I will discuss more of the details of the eChucK implementation.  Happy reading!