"Tremolo," as defined in professional music dictionaries including
"The Harvard Dictionary of Music" by Willi Apel, is the rapid
reiteration (or repetition) of the same tone, produced by rapidly
reversing the bow on stringed instruments.

"Vibrato" is the fluctuation of pitch.  Apel admits that while this
is the standard terminology for orchestral instruments, vocalists are
somewhat confused about usage and sometimes use "tremolo" when they
mean "vibrato."

In my entire orchestral musical upbringing, I never heard a musician
use the word "tremolo" to mean variation in pitch until I spoke with
organists.

Unfortunately, the mechanical music world has copied the technically
incorrect use of the word "tremolo" as used by pipe organ builders when
referring to an imitation of vibrato, produced by the pulsation of the
wind supply, which shakes both the loudness and pitch.

Many builders of orchestrions and violin-playing machines originally
used the correct term "vibrato," not "tremolo," to indicate the
fluctuation of pitch, including the Ludwig Hupfeld Company, maker of
the Phonoliszt-Violina and many different types of orchestrions.

The Mills Novelty Company of Chicago, maker of the Violano-Virtuoso,
used the incorrect term "tremolo."  Mills also used other questionable
terms, such as "damper on" to indicate "sustaining pedal mechanism off"
(or dampers resting on the strings), and "damper off" to indicate
"pedal on" (or dampers lifted off the strings).  No other manufacturer
ever used this reversed terminology.

Many dance organ builders used the term "tremolo" for two different
effects, and still follow this usage today.  In a dance organ with both
types of mechanism, "General Tremolo" refers to a device that rapidly
turns the wind supply on and off, in imitation of the orchestral string
instrument tremolo.  "Jazz Tremolo" indicates one of several types of
mechanism that rapidly vary the pitch of each pipe without varying the
air pressure.

In my writing, I stay with the traditional usage of "vibrato" for
violin machines and orchestrions, and "tremolo" for dance organs.

In the Mills Violano-Virtuoso and the Hupfeld Phonoliszt-Violina, the
strings are tuned with the vibrato mechanism at rest.  In each brand,
the vibrato mechanism raises the pitch above the correctly-tuned note
and never lowers it below that pitch.

In most solo violin pianos and sophisticated orchestrions that use
violin pipes to simulate the tone of a violin -- including the Weber
Unika and Maesto, all Hupfeld Pan Orchestras having bellows for an air
supply, and the Philipps Paganini -- the vibrato mechanism causes the
pitch to rise above the tuned pitch, not drop below it.  The pipes
frequently play without vibrato, so if they were tuned below pitch they
would be out of tune whenever the vibrato mechanism was not called for
by the music roll.

In dance organs, the jazz flute and vibratone pipes are also tradition-
ally tuned to the correct pitch with the tremolo mechanism off, and
waver above that pitch, not below it.

In most theatre organs, the tremolo mechanism momentarily exhausts air
from the pipe chest, causing the pitch to waver below the tuned pitch.
Because the tremulant (or tremolo mechanism) acts on the wind pressure,
it varies both the loudness and pitch.

Art Reblitz