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Esterline Research&Design
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Re: VCO
Esterline Research&Design   8/5/2014 1:56:04 PM
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Definitely the most FUN use of electromagnetic energy at least!

At a $300 price point, it's hard to go wrong.  Nice job Moog!

bcarso
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Re: VCO
bcarso   7/29/2014 12:37:54 PM
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Indeed not!  Moog was a clever circuit designer and exploited the then-recent availability of plastic-packaged transistors to come up with his series of modules for his patchcord-programmable analog syntheziser.  The VCOs were based around unijunction-transistor sawtooth oscillators and an overdriven transistor stage converted the sawtooth to a triangle waveform. Comparators allowed these to become rectangular waveforms and a nonlinear network converted the triangles to pretty decent sinusoids.

An exponential converter had a current output which determined the slope and hence frequency of the unijunction oscillators, thus allowing a conventional delta V in to octave of frequency output.


They were fun to use but had a lot of temperature drift. I knew this well as I was briefly the studio engineer at UCLA circa 1969.

 

Brad

resistion
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CEO
Re: Why use theremin example
resistion   7/27/2014 1:23:44 PM
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Yes exactly, and it can even be fretless stringed instruments or piano as well.

R_Colin_Johnson
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Re: Why use theremin example
R_Colin_Johnson   7/27/2014 1:06:23 PM
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An Ebow on a MIDI'd guitar could control a synth with more control over notes since you've got frets. Is that what you mean?

resistion
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Why use theremin example
resistion   7/27/2014 10:03:20 AM
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Ebow is a better musical electronic example. Of course, it's still analog, but the instrument it acts on can be MIDI'd.

elctrnx_lyf
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Re: VCO
elctrnx_lyf   7/25/2014 4:33:12 PM
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Probably the creative use of the electromagnetic energy of all time.

tiorbinist
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Re: VCO
tiorbinist   7/25/2014 11:22:07 AM
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Oh, there's nothing saying that it is physically impossible to play the melody of the Doctor Who theme on a theremin. I was just pointing out that such a rendition has never been used for theme music of the show itself.

With that said, though, it should be noted that playing the theremin is unlike any other instrument on earth, including many of the electronically- or acoustically- similar instruments. This is because there is _nothing_ to provide physical feedback from the instrument. 

You can (if it is properly designed or there is a sufficiently insulating material around it) rest your hand on the volume antenna, so you have a place to start from. But the pitch antenna is, in a tactile sense, never part of the equation. You literally "play the field". The field's shape in 3 dimensions is somewhat unintuitive, as well. 

On the violin (the instrument upon which Clara Rockmore demonstrated such prowess that she was admitted to the Conservatory at the age of 5), one has one's pitch hand anchored to the instrument as a reference, and can feel the curves at the ends of the neck, as well as the strings under fingertips. Wind instruments have holes or keys that you can feel, pianos have keys (quantized pitches in 8/7" divisions for the white keys!). Starting these instruments is not easy, but you have something to _touch_.

Not so the Theremin. Instead, you move your hand through an electrical field, adjusting the frequency of one oscillator, which beats against another, fixed oscillator, to provide the pitch as the beat between the two (radio frequency) oscillators. If any thing in the field moves, the field shape changes, and if the thing provides the same kind of capacitive effect as your hand, it changes the pitch for you. Thereminists need their personal space (to a radius of about 10'!)

Some theremin designs provide a linear field strength on a radial path from some point on the pitch antenna, where you'd like to have your hand. But if you move from your practice room to a stage, that particular path might also change. 

God forbid you should be on stage with 10 other thereminists! (It _has_ been successfully done, though!)

So the question of whether _you_ could play the Doctor Who theme on a theremin is not so much dependent on the theremin as on you.

Fortunately, there are some things that help. Because the Theremin oscillators are always on (the volume system is a controlled amplifier, rather than an on-off/level control for either of the actual oscillators) the pitch is _there_, somewhere, even when the instrument is silent. Some thereminists have made use of pocket earphone amps with sensitivity to the RF field's beat frequency to allow them to hear the pitch and get their hand in the right position before "opening the throttle" and letting the sound out. Others have developed systems that pick the pitch off before the volume-control circuit to provide this preview. (And, of course, some thereminists don't bother with specific note pitches, but use the theremin as a sound effect or as part of formally-composed "noise" performances.) But even then, moving from pitch to pitch with the right hand flailing in the air while crafting the volume envelope of each note with your left hand (which is recommended even for lefties, but not always adhered to!) requires a certain amount of physical stamina, agility and practice, while learning the notes really does require a certain amount of pitch acuity and, one prays, talent in music.

RCA advertised the theremin as the instrument that required no actual musical ability: "If you can hum (or whistle) a tune," the ads claimed, you can play the Theremin. 

 

In actuality, the theremin requires a lot of musical ability _and_ a lot of electrical engineering/RF knowledge, as well (as we've discussed on the LEVNET theremin discussion group) some knowledge of proper ESD protection strategies, all added on top of the basic electrical and electronic knowledge any rock guitarist needs to avoid electricuting themselves or having Mr. Edison humming along tunelessly.

Etmax
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Re: VCO
Etmax   7/25/2014 10:46:42 AM
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It never ceases to amaze me how far in life you can get with an untruth in your mind stored as fact because someone you thought was wise said something you thought was true.

I now stand thoroughly corrected on this subject and I thank you for your detailed insight into that legendary piece of music.

You've probably now also saved me the disappointment I might have had, had I built the theremin I wanted to, to be able to play that tune :-)

Truely thanks, it was interesting.

Douglas442
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Re: VCO
Douglas442   7/25/2014 4:04:27 AM
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tiorbinist said:  "Although Moog had been designing and making (and publishing articles in Radio-Electronics and selling kits for) theremins since the early 1950's, the Doctor Who theme did not use one.

Instead, Derbyshire and Mills used banks of oscillators and white noise, coupled with Music Concrete processes to make the theme music. They recorded each sound on tape, adjusted and rerecorded to get all the reqired pitches, hand-tuned oscillator dials to get the sweeping melody, etc, then literally cut and taped together the sounds to produce the master tape."

 

And, as if that weren't example enough of making creative use of "old-school" techniques... producing the TARDIS dematerialization-sound, originally created by one Brian Hodgson of the BBC Radiophonic Workshop, involved using a door key to scrape the strings of a mechanically gutted piano. 

The recorded sound was speeded up, slowed down, mixed, and embellished with some basic electronic effects, but it's still interesting to note that it's raw source involved some relatively simple, but clever, acoustical methods.

R_Colin_Johnson
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Re: Air Guitar V2
R_Colin_Johnson   7/24/2014 9:16:41 PM
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Cool demo! Thanks for the link :)

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