Subj : Theremin / Mellotron
To   : Martin Ridgley
From : MIKE ROSS
Date : Tue Nov 07 2000 03:47 am

"Martin Ridgley" wrote to "STEPHEN JONES" (02 Nov 00  16:47:00)
 --- on the topic of "Theremin / Mellotron"

 -=> STEPHEN JONES wrote to BRETT MCCOY <=-
 SJ> Is the Mellotron a keyboard instrument?

 MR> Yes.

 SJ> Also, is it related to the Theron (sp?) that they used to do
 SJ> weird sounds like in the movie "The Day The Earth Stood Still"?

 MR> 'Theremin' is the correct spelling and it's not related to the
 MR> Mellotron at all.  The Theremin was one of the earliest electronic
 MR> instruments - invented around 1920, IIRC - and it's a pretty unique
 MR> electronic instrument, unlike anything else I can think of.
 MR> You can hear one on the 1966 Beach Boys hit, "Good Vibrations".
 MR> It's the instrument making the spacey, wavering sound at the very
 MR> end, as the song goes into the instrumental outro and then fades.

 MR> I don't fully understand how they work, so I'd best leave that
 MR> for someone else to explain.  I *do* know that the original ones
 MR> were notoriously difficult to play with any accuracy, and that's
 MR> a big reason why the instrument didn't catch on.  They were used
 MR> mainly just for sound effects - often in sci-fi movies, like the
 MR> one you mentioned.

 MR> I've noticed the Theremin showing up on a few fairly recent pop
 MR> recordings, though - most notably, Matthew Sweet's latest album,
 MR> "In Reverse" (1999) where it's used on 6 of the album's 14 tracks!

The basic principle of the theremin is that of beating (sum and
difference frequencies) between two radio frequency oscillators. We've
all probably experienced this whistling effect when listening to a radio
while tuning the dial between stations especially on shortwave. This
beating of radio frequencies is also known as the heterodyne principle.

The theremin therefore consists of at least two beating radio frequency
oscillators which are mixed together in a detector circuit (heterodyne).
One of the oscillators has an aerial antenna connected to its frequency
setting resonant circuit. The proximity of any object will upset the
resonant circuit capacitance which will alter its oscillation frequency.

Normally the two oscillators are tuned to the same frequency or zero
beat but when a hand is brought near the aerial it alters one oscillator
frequency. This new frequency beats with the other oscillator to create
a difference frequency in the audible range. By varying the distance of
the hand the audible beat frequency can range anywhere in between a low
rumble to a fine whistle.

A refinement to the basic principle is in using a third radio frequency
oscillator, with similar aerial, to control the loudness or volume of
the first oscillator pair beat tone. Thus a theremin will have two
antennas, one for each hand, one controlling pitch and the other volume.

The performer then stands in front of the instrument and simply waves
his hands about in the air near the antennas (without touching). It's
apparently a rather difficult instrument to play since there is no
visual reference to the pitch like a keyboard or a fretboard gives.

I've found plans from one of the many internet guitar sites (Leper's?).
Similar instruments to the theremin have been made using light beams and
ultra sonic sound instead of beating radio frequency oscillators.

Hope this wasn't too long an explanation...

.... Accordion: A bagpipe you can't fold quietly.
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