Vibrato and Tremolo
The terms vibrato and tremolo are sometimes used interchangeably, although the strict definitions of each describe them as separate effects: vibrato is a periodic variation in the pitch (frequency) of a musical note, whereas tremolo usually refers to periodic variations in the volume (amplitude) of a musical note. In practice, it is difficult for a singer or musical instrument player to achieve a pure vibrato or tremolo (where only the pitch or only the volume is varied), and variations in both pitch and volume will often be achieved at the same time. Electronic manipulation or generation of signals makes it easier to achieve or demonstrate pure tremolo and/or vibrato.
There are some instances where one of the terms (vibrato, tremolo) is used to describe the effect normally associated with the other term. For example, vibrato is sometimes referred to as tremolo, notably in referring to the vibrato arm of an electric guitar as a "tremolo arm", which produces variations of pitch. Conversely, the so-called vibrato unit built in to many guitar amplifiers produces what is known as tremolo in all other contexts. See vibrato unit for a detailed discussion of this terminology reversal.
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