The literal definition of the Italian word ‘Rubato’ is ‘robbed time’, which doesn’t seem to be a particularly attractive way of describing something that adds such emotional meaning to a piece of music. In essence, it is where music is slowed down or speeded up to create an expressive effect. When done with artistry and musical sensitivity, rubato can subtly ebb and flow but without distorting the rhythmic pulse. What is taken away is always added back, rubato would never slow a pulse down and then not regain it later on, it is in a sense elastic.
In the studio, the only way of effectively playing rubato in an ensemble is through playing ‘live’, where all the session musicians are actively listening to each other and making minute adjustments as they play. It would not be possible to achieve a natural ‘pulling up’ or quickening with a click track. A click track is frequently used in recording situations, especially where string parts are to be added over existing instruments or vocals – it takes the form of a metronome beat heard only in the headphones of the session musicians who are working on the track. A click can be speeded up or slowed to suit the beat of the music players are working on and can even accelerate or slow down, but this rarely sounds very natural.
When music is of a metronomic nature (such as rock or pop music), then a click track can be highly effective and when used well, will not be betrayed in the end result. Recordings can sound perfectly natural where a click track has been used and often can have a tightness and accuracy that could only be achieved with a lot of rehearsing. Of course, if multiple overdubs are used then a click track is an essential tool and will cut down the studio time needed.
In more sophisticated music which is ever changing, the use of a click track can be more of a hindrance than a help and in that situation, musicians opt to use their ensemble skills and the end result will hopefully be far more natural.