Saturday, February 15, 2003

Sign of the times

I went to Sam's Club yesterday to pick up a few things when I saw a special offer. For $12 I could buy a set of three large maps - one of the US, one of the world, and one of Iraq.


A Baha'i visits Haifa.

Friday, February 14, 2003

I'll support animal rights when:

Possums are traffic cops (no, not this one)
Bugs are air traffic controllers
Birds wash cars
Bears use toilets
Dogs teach etiquette
Deer run auto body repair shops


No despots allowed

Ya know, that Saddam Hussein guy is disgustingly rich and can do pretty much anything he wants (as long as it's 50 feet underground or on the run). Kim Jong-Il lives in obscene luxury while his country starves. And although he is reviled wherever people bathe, think, and respect human life, the late (?) Osama bin Laden is revered by uncounted hordes.

But despite all their wealth and fame, there is something they simply cannot have. They can't come to Midwest Blog Bash IV next Friday. (Well, I'm being a bit presumptuous here. This is a Charles Austin production, so he's in charge of guests, venues, call-ins and whatever else. As of yet he hasn't told me exactly where it's going to be, so I may be sitting home like Saddam & Co. myself.)

Are YOU good enough to share the exalted company of Austin, Juan Gato, Chris Johnson and your humble author? Or are you going to piddle away your time, say, seeing 'Les Miserables'? Past events have drawn guests from as far away as Australia, and this time promises visitors from such exotic places as Arkansas.

For more details, keep an eye on Austin's site. Past practice has been that to let the host know if you're going to show so he can make the right arrangements (it can be tough to book the Edward Jones Dome on short notice). Just send him an email (charlesaustin at earthlink dot net), if only to congratulate him for his 1st blog anniversary, 29th birthday (?), 77th Scourge of Richard Cohen™, and 4th place finish as "Best Fisker".

See ya in Kirkwood.

Guitar science 103 - the pickups

So what happens from the time the guitarist picks strings to the time the sound comes out the amplifiers?

Problem number 1 is that we don't know how to amplify sound waves directly in a way that permits much control. So we must convert the vibration into something that can be controlled more readily. The obvious choice is an electric signal, if only because it is the most easily manipulated, several phenomena can be used, and transducers are readily available.

So what's a transducer? For our purposes it's a device to convert one type of signal to another. Microphones, speakers, light meters in cameras, speedometers and countless other devices have or are transducers.

I already mentioned a transducer that could be used for the guitar - a microphone. But look around and you'll rarely see it. The problem is that they can pick up a lot of things besides guitar strings, leading to noise. To avoid this, we want something with "tunnel vision".

OK, we can measure other things about the string that aren't likely to be influenced by other signals. They are simple, but in fact their lengths, displacements, and tensions are varying in time with the vibration. We have we have common types of transducers for all of them.

The length could be measured dynamically in various ways. An electrically conductive string's resistance would vary over a narrow range, but that means you need a power source inside the guitar to power the ohmmeter. If the string could function as a fiber optic cable, the relative phase angles of the light transmitted and received could be used to measure the length changes. I suspect that all would pose amplification problems too - each string might need its own electronics to make sure that their signals all had the same relative strengths. Give me the money and I'll cook something up for you, but in fact to my knowledge neither of those offers enough additional benefits to justify the added costs and inconveniences.

How about the varying tension? For this we have piezoelectric devices, which respond to pressure changes. The resulting signals are unlikely to be contaminated with extraneous data. They may need a bit of cleanup and reinforcement first, but then they can be sent to the amplifiers.

The last alternative is the varying position or displacement. For this again we could use optical or other phenomena to measure, but in practice what has been most practical is to use magnetic pickups. This limits the materials we can use for our strings, and some would prefer materials that won't work such as gut or nylon. But it so happens that the materials we can use, such as steel, have virtues of their own, and if you go to buy strings the steel ones are far easier to find.

A typical magnetic pickup consists of a set of small permanent magnets wrapped in wire and connected together. Accordingly they impose a magnetic field on the surroundings. As the strings vibrate within that field, they cause the field to vary in the vicinity of the wires wrapped around them. When you vary a magnetic field in a conductor, you induce voltages in the conductors. These tiny voltages are sent to the amplifier for reinforcement.

Given that the magnetic pickups sense the relative motion of the guitar and the strings, and they are intended to measure the motion of the strings, it is important that they are rigidly mounted to a stable base. Otherwise you're also measuring the vibration of the guitar body too. This is especially important at high volumes, or else feedback can be uncontrollable. So guys who play loud, with exceptions like Ted Nugent (who else?), generally play guitars with solid bodies.

Terrific, we have a signal that varies with the frequency and the power of the input. But we're not through yet - hook this straight to a speaker and you'll get jack squat. What you need is more power. And Joe Schmoe on the street can guess that that calls for amplifiers.

Alright, this is long enough for now. It was going to be about all of the electronics at first, but it kept growing even faster than this sentence. Stay tuned for more boundless excitement as we venture into the wonderful world of Amplification! and Strings!

Tuesday, February 11, 2003

Just asking...

Celebrities say stupid things all the time, but they always seem to outdo themselves around Oscar time. Am I wrong in suspecting that they think it will increase their chances of winning?

Be in style...

Get your Gross Anatomy clothing here, from Beth.

Sneeze hustling?

Right here.


Dodd for President

Guitar science 102 - the bodies

I have to wonder just how long people fooled with the design of guitar bodies before they came up with the modern acoustic guitar. There are so many things to get wrong. The type of wood, the aging, the dimensions including thickness, the finish, the gluing and bracing, the size, shape and location of the soundhole(s), the joining of the neck, placement of the bridge....

All of this is critically important in creating the mechanical amplifier that is an acoustic guitar. Variations will deaden the sound, lose the amplification, change the tone or intonation, or might even cause the guitar to collapse under the stress of string tension.

The overall shape of the guitar is intended to be shaped like a woman. Mercifully, they fed their women in those days, and the early guitar makers (known as luthiers because in times of yore they made lutes instead) built them accordingly. Fortunately Kate Moss wasn't around back then. (Although she could have inspired the dulcimer).

Anyway, this complex shape results in complex vibration patterns in the guitar body. The result is a vibration pattern that needs two dimensions to describe it, and it defies neat analysis. The result was that building guitars right required a fanatical attention to detail by people who weren't always sure exactly what they were doing right.

Then along came a guy named Charles Kaman. He was a guitarist and an aerospace executive who possessed the talents and the resources to analyze good-sounding guitars in great detail. By using sophisticated instruments, he was able to determine exactly how good guitars vibrated, and then was able to recreate this behavior in mass production. Eventually he came up with Adamas guitars, with their historically strange body designs and soundhole patterns.

But acoustic guitars were doomed because of their low volume. Big bands would drown out guitars, so they needed sound reinforcement badly. So people like Charlie Christian started using amplification.

Then they ran into another problem. Recall that everything has a fundamental frequency for vibration. As a result, when they are subjected to sounds at this frequency, they start vibrating themselves. Under the right conditions, this "feedback" builds on itself, causing screeches and worse and possible destroying equipment and eardrums.

The amplification of a acoustic guitar depends in part on the guitar's body vibrating readily at the frequencies a guitar produces. Thus they were highly susceptible to feedback when played near their amplifiers. What to do?

Then came Les Paul, a guitarist and recording pioneer. He realized that if you were going to use electric amplification anyway, who needs acoustic amplification? Electric guitars needed to eliminate this vibration as much as possible, and one way to do this was to make the body very stiff and dense. This ultimately resulted in the famous Gibson Les Paul guitar which is manufactured to this day.

Thus the shape of an electric guitar has little to do with its sound. Most continued to follow the general outlines of an acoustic guitar only with necks mounted at a higher fret and cutaways for better access in the high ranges. But then there were Flying V's, Explorers, the Stick, and many more oddball shapes to come.

OK, but how do you amplify them? Stay tuned for guitar science 103 - the electronics.

Guitar science 101 - fundamentals

Any good-sounding stringed instrument is an engineering marvel. So much has to be right to achieve the right sound. Yet to this day scientists have things to learn about it.

Anything made to vibrate in the air will cause the air to vibrate too. The degree of vibration we perceive as volume, the fundamental frequency of the vibration is what we perceive as pitch, and the higher harmonics of the fundamental combined with the mechanical amplification produce what we perceive as the timbre.

Fundamental frequency? Give anything a whack and it will start vibrating and continue until the energy of the whack dissipates through sound energy and the internal friction or damping within the object itself. This vibration is a function of the density, stiffness, geometry and various other characteristics of the object - whack it again, and if you don't bust it the pitch will sound the same. The loudest and lowest sound you hear is the fundamental frequency (although you may not hear anything - nominally humans can't hear anything any lower pitched than 20 cycles per second, or any higher pitched than 20,000 cycles per second. Actual humans do far worse, including a lot of guitarists.)

A guitar string is about as simple a case to analyze as there is, but it's not trivial. For analytical purposes we act as if it is stationary at the bridge (which holds the strings off the body) and the nut (which holds them off the neck) and it is "taut". So how many different ways can it vibrate?

Well, for starters we can vary the tension. As we tighten the string, the forces tending to pull it back straight again after it is plucked become stronger and thus pull it back faster. The result is a faster vibration and a higher pitch.

Or we can shorten the string, perhaps holding it down against the neck with our fingers or a capo, or holding a stiff slide against it. As the string shortens, the vibration rate increases and the pitch increases, and vice versa.

Alright, suppose we keep the tension and length constant - now how many ways can it vibrate? Believe it or not, there are an infinite number of ways. It can vibrate such that the string forms half a wave, a full wave, 3/2 of a wave....n/2 of a wave. Each of these has a different pitch. The lowest pitched of these, corresponding to half a wave, is called the fundamental frequency, and all of the rest are called harmonics.

The fundamental and the harmonics can all occur at once, in various relative strengths depending on where we pluck it. Close to the middle emphasizes the fundamental (it sounds more like the tones from a phone), close to the ends emphasizes the harmonics (it sounds "brighter").

Actually you can kill the fundamental and other harmonics in certain ways. If you lightly touch the string halfway down (12th fret) as you pluck it, you'll hear the 1st harmonic dominate. It is twice the frequency of the fundamental, and musically is one octave higher. (If you're not a musical person, think the "Hi Ho" when the elves sing in Snow White). If you do this 1/3 of the way down, (the 7th fret), you'll get a note that vibrates at 3 times the rate of the fundamental, and in musical terms is an octave and a 5th higher. At 1/4 of the way down (5th fret) you'll get one 4 times the frequency, or two octaves higher. And so on - higher octaves don't land exactly on frets.

You'll hear some of this in a number of Eddie Van Halen solos ("Spanish Fly", for one), and Steve Howe's solo at the beginning of "Roundabout" by Yes.

You can also kill the fundamental by striking the string with the thumb and pick at the same time - Billy Gibbons does a lot of this at the end of ZZ Top's "La Grange" and Gary Richrath of REO Speedwagon did it a lot too. They often bend the string at the same time, producing a whistling or squealing sound.

Yes, you can bend the strings, pushing them slightly to the sides. This lengthens the bent string but also tightens it. The tightening effect predominates so as to raise the pitch of the resulting note.

The tightening can be done in other ways too. Some players will push down on the strings behind the nut. Others will bend the neck of the guitar or shake it. And there are vibrato arms (aka wang bars, whammy bars) that can be used for various loosening and tightening effects like "dive-bombing".

When a note is held for a decent length of time it is usually given some vibrato to make it more "interesting". The string is alternatively bent and relaxed, which varies (modulates) the frequency. It can be subtle or very obvious, such as in "Who's Sorry Now" by Journey or "Back in Black" by AC/DC. (Frequency modulation - where have you heard that before? Uh huh, it's how FM radios work. You tune in to a "fundamental", and the FM superheterodyne circuitry deciphers the "vibrato" - wider variations=>higher volume, faster vibrations=>higher pitch).

You can also effectively vary the length of the string, usually by holding the string lightly against the neck or a fret. Vibrato can be achieved this way too, but rolling the fingertips along the strings instead of displacing the string parallel to the neck like a violinist.

Another way to vary the effective length of the string is to use a slide, usually of heavy pipe or glass like a bottleneck. With it you can achieve some strange pitch effects, like the bird chirping at the end of "Layla" by Derek and the Dominoes. Some of my favorite slide work is in the solos for "Like a Rock" by Bob Seger and "Fool for the City" by Foghat.

Of course this mainly applies to steel strings. Nylon or gut strings are too stretchy to bend well - you have to move them too far. That means subtler vibrato at best, and the music written for them usually has more strings being played at once and shorter notes.

Well, that about does it for the basics. Next - the bodies.

More rules to live by

Don't talk dirty to the Chief of Police.

Sunday, February 09, 2003

Doggie style

Michelle offers a gift to the leftists. Then in the comments the Cracker Barrel Philosopher posts a cartoon that fits the French and Germans to a T.