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Vibrato or Tremolo?
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A Layman's Viewpoint | A Technical Viewpoint
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A Layman's Viewpoint

The History of Tremolo and The beginnings of Vibrato

Simply put, Tremolo is a cyclic change in volume. Tremolo, a.k.a. amplitude modulation, is a very pleasing effect and probably the first built into an amp, starting in the late 1940's with Danelectro, Gibson, and Premier. In 1955 Fender introduced the Tremolux (model 5E9). This was Fender's first amp with Tremolo. Meanwhile, in nearby Inglewood, Magna Electronics known for student lap-steel/amp combos was manufacturing real professional amps that incorporated unique designs and revolutionary new features such as Stereo Vibrato.

So in 1956 Fender introduced the Vibrolux. The Vibrolux supposedly had Vibrato (pitch modulation), but in reality this was just another variation on the Tremolo already found in the Tremolux. In fact, NO Fender amp has EVER had true pitch-bending vibrato, regardless of catalog hype to the contrary.

Try this Experiment at Home

Plug your guitar into your amp and power it up. Now strum a chord and turn the volume control up and down rhythmically and repeatedly. You will hear Tremolo. This is what Fender and many others called Vibrato.

Now try this

Fret one of your guitar strings and rhythmically rock your finger back and forth in a sideways motion stretching the string slightly. Notice the pitch is changing, This is Real Vibrato.

Don L. Bonham's Patented Vibrato Circuits

Sometime in the 1950's, Magna Electronics Inc. started to manufacture the now famous Magnatone guitar amps. They were the first and only guitar amps with real Vibrato. Vibrato a.k.a. frequency modulation, is a cyclic pitch change. Magnatone amps had great tone and features, but were under powered, too heavy, and exspensive compared to the market leaders, Fender and Gibson. These other amp manufacturers probably knew this and were quick to change their amp labeling and advertising to indicate that their amps also had Vibrato. Even the Vibrosonic, made by Fender in 1959, had only a complex Tremolo circuit.

On June 13, 1961, Don L. Bonham was granted a U.S.Patent # 2,988,706 for his Vibrato circuits. By now the Estey Organ Company had bought Magna Electronics and redesigned many of the amps. Magnatone amps were still the only ones with electronic Vibrato but by 1965 Fender and the others had the bigger share of the Market. Well why not, their guitar amps supposedly had vibrato and were less exspensive. To this day the only guitar amp that effectively incorporated Real Vibrato, was the Magnatone line of Amps.

There are other acoustic and electronic ways to make Vibrato i.e. Leslie's Doppler effect and Hammond's distributor RC Network, but none is as magical as the "Golden" Voice of Magnatone. This is what the Vibroman 2.0 Stereo Tube Effects is designed from, using the very same Varistor arrangement as the Magnatone Model 280.

Written by Greg Zaccaria, Owner Zack Engineering © 1996



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SIMULATED SCOPE VIEWS

Whether the amplifier is labeled Tremolo or Vibrato, the truth is seen on the scope with a 1Khz sine wave. Scopes were provided courtesy of STEVE at TEKTRONIX Inc.
Simulated Tremolo
Animated Scope Tremolo will always show up as amplitude or volume going up and down. This is typical of most amplifiers. i.e. Fender etc., even some newer Estey/Magnatone amplifiers.
This is Real Vibrato
Animated Scope Vibrato, on the other hand, will always show up as pitch shift or the phase changing back and forth. This is the effect that some Magnatone Amplifiers were famous for, Real Vibrato.



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A TECHNICAL VIEWPOINT

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Tremolo and vibrato sound much the same. And to tell the truth, while some theoreticians will spend considerable time discriminating between the two, when referred to an electronic "signal" as seen on an oscilloscope before it reaches the loudspeaker and in terms of propagated waves (the kind we listen to and call sound) there is little absolute difference between the forms.

This can be shown by a frequency analysis of the two forms. Academically, tremolo is a fluctuation of amplitude applied to a sound of constant frequency. In traditional instruments it may be achieved by opening and closing a shutter that attenuates the sound passing through it. The old home harmonium of a few generations ago did this, with the name "vox humana" (not to be confused with the true stop of that name on professional organs). Vibrato is a variation of pitch, a fluctuation of frequency, applied to a sound of constant amplitude. In traditional instruments, the best known example is the way a guitarist achieves the effect by trembling his hand so his finger rolls the string at the point where it touches the fret board.

In an electronic organ, as well as introducing vibrato by changing the oscillator frequency, it can be achieved by moving the loudspeaker assembly or by using a baffle that has the same effect by changing the distance the sound wave has to travel to escape into the room. This kind of speaker is commonly called a "Leslie" after the first one of its kind to achieve the effect.

Suppose a frequency is modulated in one or the other of these ways, electrically or electronically, at a rate of 6 Hz, which makes a good vibrato or tremolo rate. Say the frequency is a concert pitch A of 440 Hz. The pure tremolo, or flactuating amplitude, (such as found in "Fender" amps) will add frequencies of 434 and 446 Hz, in equal proportions and phased so that together they alternately add to and subtract from the steady 440 Hz waveform, without shifting the phase of the resultant wave. So the frequency content of a concert A with tremolo is a dominant 440 Hz with smaller (and equal) amounts of 434 and 446 Hz.

Now assume the frequency is shifted at the same rate, in what is called vibrato. Frequency or pitch shift can also be interpreted as phase shift. When frequency is raised, phase advances; when frequency is lowered, phase delays. They are not the same but are related. They can be reguarded only in interchangeable terms so long as frequency is repetitively changing as happens in vibrato.

If the same frequency, 440 Hz, is alternately advanced and retarded in phase at a rate so that the complete variation is repeated six times a second, the frequency will wobble above and below 440 Hz while maintaining that average value. How far above or below 440 Hz the frequency swings will depend on how far the phase shifts from its median value in each one-twenty-fourth of a second (a guadrant of the 6-Hz variation).

Regardless of how far the frequency shifts, the fact that its rate or repetition frequency is a 6 Hz means that the phase movement repeats at that rate. Consequently, the most dominant effect in an analysis of the frequency content will be the same two frequencies produced by the tremolo but in different phase relationship.

To keep the amplitude constant, if more than a few degrees of phase change occur other sideband frequencies such as 428 and 452 Hz will have to be added. But the dominant ones will be still be 434 and 446 Hz. And in a practical situation, a warbling tone will seldom fluctuate only its amplitude or only its frequency without affecting the other.

Even when the tone generated is produced by pure frequency or pure amplitude variation, the acoustic wave it produces has to travel round a room with real dimensions before we hear it. Thus the wave delivered to the loudspeaker may be pure tremolo, for example, but before it has left the diaphragm very far, it will have components of vibrato in it as well because of the phase shifts that occur as the various component-frequency waves travel across the room, or vice versa.

Admittedly, vibrato can give a richer sound than tremolo, for a reason that should be fairly obvious from the foregoing discussion. In generating tremolo the only extra frequencies added are a single pair of sidebands. A deep vibrato can add quite a number more frequencies. But a shallow vibrato produces essentially the same frequencies as tremolo.

Where the tone being modulated has a relatively high frequency, a vibrato will cause the phase to "go round" a few times at least, compared to a wave of the same steady frequency. This means that tremolo cannot possibly have as many extra frequencies, although the fluctuation might otherwise be as deep. But where the tone being modulated is low in frequency, as in the bass notes, the phase shift corresponding to vibrato will be relatively small because there will not be enough cycles above or below the normal frequency to allow phase to shift very far. This means that for low notes tremolo and vibrato become virtually indistinguishable.

You might be able to tell the difference by looking at the waveform on an oscilloscope screen before it goes to the loudspeaker, but if you pick up the same sound with a microphone and put it back on the oscilloscope screen you would have virtually no means of knowing how it started.

From the musical viewpoint, a violin can be played vibrato, and it is not impossible to play a guitar that way. However, in order to get a pure rhythmic vibrato sound from a guitar - without getting hand cramps or using a whammy bar, it must be done electronically.

Courtesy of N.Crowhurst, Electronic Musical Instruments © 1977

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