These 2 different effects are probably the most confused effects with musicians and manufactures alike. What effects do is vary the outputted sound in some fashion, as for example the over-drive pedal which is excessively used in heavy metal bands. These effects both operate with the modulation or by changing the modulation of the sound waves. Sounds waves can be altered by natural means, or by a musicians technique or by using electronic devices to digitally distort and/or enhance the sound.
Effects have been around for many years, and are more common in certain types of music as opposed to others. For example heavy metal makes excessive use of both of these effects by using electronic filters to modify the sound. Effects can occur naturally, be created by an artists or musicians techniques or as the heavy metal example can be created by electronic aids or filters. Electronic keyboards, for example, have these effects and many others built in.
The purpose of an effect is of course to create a more interesting sound or vary the note or pitch in some minor fashion. Sometimes effects are over emphasized to create a shocking or noticeable sound change or are simply used to add more flair or interest to a musical song. Vibrato and Tremolo are two of the most common and most confused effects. This comes in part because of the famous tremolo bar on the guitar, as used by Jimmy Page among others, and especially preferred by blues artists.
The tremolo bar on a guitar is not really a tremolo bar at all, rather it produces a vibrato effect. A vibrato effect is something that causes the pitch to vary either higher or lower from its current pitch. This is basically a modulation effect which results in the pitch being varied in a modulated fashion by going higher and lower, but also produces a rhythmic effect.
Now the real Tremolo effect does not actually vary the pitch at all, it changes the amplitude and volume of the sound and is a constant repetition of a sound with higher and lower amplitudes. An air-raid warning siren would be an example of the Tremolo effect, where a sharp pitch starts at a low volume and then gradually modulates up to a higher and more intense volume, but the pitch and tone does not actually change.
Both the Tremolo and Vibrato effects work on changing the modulation of any sound wave-length, but the Vibrato effect changes the pitch modulation, while the Tremolo effect is a rapid variation of volume, or intensity.
Many common amplifiers on the market, as made by Marshal or Fender include both effects built-in as standard features. A musician can also acquire both types of effects in their respective pedals, for use with Guitars, or keyboards or any amplified instrument.
Many artists will combine both effects in different ways and various music styles make more use of one effect versus the other. For example, Blues songs, play a lot with bending notes or varying the pitch. This can be accomplished of course by bending the notes with the finger, or if its a wind instrument by bending the notes through air control or through the instruments valve control. Flamingo and Spanish music makes constant use of the Tremolo effect by rapidly repeating notes using the strumming hand, in an arpeggio fashion.
A vibrato effect pedal serves to bend the entire musical sound of all combined notes as a single entity instead of bending just a single note. The same can be said for the Tremolo pedal effect. A tremolo effect is more useful for creating a pulsating effect or cascading sound that goes louder and quieter in a pulsating fashion. There are also pedals like the TremOVibe that produces a combination Tremolo and Vibrato effect.
There is a certain overlap between the two different effects, and such they are often confused or used inter-changeably between musicians and music professionals. For example the Strato-caster whammy bar, is thought to produce the tremolo effect but it actually creates a vibrato sound.
Both Vibrato and Tremolo can be reproduced electronically, or by physical means, as in variations in a singers voice, or how the musicians plays his or her instrument. Vibrato adds flair to a singers voice, but not all singers can accomplish it, and it takes either a strong natural ability or strong classical training to develop the technique.
Vibrato can be achieved on the Guitar rather simply by just bending the notes with the playing hand, and is achieved on other instruments in different ways. For example pitch is bent on a trumpet with or without the aid of the valves by lip and breathe control. Pitch is bent on reed instruments as well by aid of the valves or by controlling the breathe.
Tremolo can be achieved in a similar fashion, for string instruments by the repetition of the strumming hand, and by wind instruments by breathe control.
There are many songs that may owe their popularity because of use or over-use of these combined effects. Some famous tremolo influenced songs are of course Crimson and Clover by Tommy James, or Give me Shelter by the Rolling Stones, or a lesser known song Crush with EyeLiner by REM.
Almost every song ever sung or every musical composition, makes use of the Vibrato effect because Vibrato is changing or bending of pitch. When these effects are amplified or over-used by the utilization of electronic sound modification systems as in pedals, or electronic effects, then they greatly distort the musical sound. This perhaps is most note-able in electronic music or experimental music that stretches the limits of listenable music to something that sounds like an alien invasion.
There is really no way to say which effect is better because basically each one has its place in almost all forms of music, both classical to modern. Vibrato exists in almost any type of musical sound, and tremolo is more of a produced effect either by technique or electronic filtering. The use and combination of these two effects makes for more interesting music or if improperly or overly used can also destroy a musical composition.