Daniel Barenboim: Tempo

Singers, often ask me what tempo I am going to take. I answer that I cannot tell until I have heard them sing, and I often give the same silly but illuminating example: when you are going on vacation and have no suitcase, what do you do? Do you go and buy just any suitcase and then decide what you can put in it? Or do you first consider what you need to take - shirts, tennis racket, rollerblades whatever - and then buy a suitcase of certain size? most likely, you do the latter. The tempo is the 'suitcase;, and the music is the 'contents'. If the suitcase is too small, you can't fit in all your belongings, and if the suitcase too big, everything floats around. Once you arrive it does not matter if the suitcase is brown and round or square and black. The only thing that matters is whether you have what you need. The tempo is therefore to provide the correct speed for the content of the music; therefore it is the last decision I make.

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I think that there is something physical in one's feeling about tempo. You should feel uneasy when a tempo is not correct. This may apply to a particular moment, in a particular place, with a particular acoustic, tension and volume. in an over resonant church you are forced to take a slightly slower tempo than in a building with a dry acoustic, because the sound needs more time to come into being.
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The other extreme is that of slowness. If there is not enough intensity in the vibrato of the strings, or in the harmonic tensions of the music, even a relatively fast-moving tempo will sound too slow. When the tempo is right, all the different ingredients can correlate with each other in perfect harmony.
When you work at an opera house and rehearse with a singer at a piano, when the weight of the sound is considerably less than that of a full orchestra, you maturally take the music at a slightly faster speed. When the sound has weight, it needs time to move. The weight of the sound is a determining factor for the correct tempo. If you ahve an orchestra able to produce the necessary weight, you can take a certian tempo more slowly. With an orchestra lacking this weight the same piece has to be taken imperceptibly faster