Are you sure? Some accounts of Alicia Della Rocha say the same thing, but in fact (according to a completely reliable authority, pianist Dean Elder who interviewed her for his book "Pianists at Play") the stretching exercises she started doing as a child worked so well she can easily do 10ths.
I have trouble imagining anyone playing the repetoire Biret does if they can't even do 9ths. Could Hoffmann do 9ths at least?
Wait a moment
What Alicia said in the book is that in her 20s playing thenth was a real struggle while now after doing lot of exercises they're not a problem anymore
It doesn't specify though is she can know play full tenths or if finding a way to roll chord tenth is not a problem any more
In her 20s she could barely reach a an octave but stretching exercise can't add up three tones to your reach, because despite stretching how the length of your fingers remains the limiting factor in your reach
After all she is 4.9 feet tall and her hands are clearly small and under average size
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There are few really large concert pianists but a certain physical size is essential to guarantee hands large enough for the wide stretches and huge chords of the international concert repertoire. De Larrocha has had to work relentlessly to compensate.
"I do stretching exercises all the time," she said in a 1969 interview. "They're a mania with me. I play stretches, for example, between the second and fifth fingers, stretching my fingers apart with my other hand. I do these exercises mechanically, on the piano. And then I play chords with the biggest possible stretches, but never until the hand is tired. That's dangerous." Those stretches have stood her in good stead to this day.
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Laurence Libin, curator of musical instruments at New York's Metropolitan Museum of Art, says pianists such as Alicia de Larrocha, who is under 5 feet tall, have overcome the apparent limits of hand size by stretching their muscles and adapting their fingering of wide chords. Some performers, he says, simply don't attempt works by such big-handed composers as Sergei Rachmaninoff. Reimann's problem, Libin says, "is an imaginary problem."
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Dr. Tinka Knopf de Esteban, a pianist with expertise in working with small-handed pianists, was interviewed and videotaped demonstrating stretching exercises learned from her teacher, the renowned pianist, Alicia de Larrocha.
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De Larrocha performs frequently in the United States, having established her place as one of the world's most formidable pianists when she made her debut with the New York Philharmonic in 1965.
Regarded by many as the most important of Spanish pianists, she is an expert on the composers of her native country. The master-class performances are heavy on those names.
"It's extraordinary insight into this repertoire," Mazzoni said.
De Larrocha also is well known for her classical playing, as well as for overcoming a physical limitation — unusually small hands.
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I'm sure other variables come into play but what is the true objective of playing the keyboard? Is it to match the way Horowitz used to play in his later performances - wrists very low? Or match the way someone with small hands like Alicia de Larrocha plays - wrists high in stretching big chords?
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There was some discussion about choosing an instrument that suited the physique of the students, although it was admitted that several artists had succeeded in spite of physical limitations, Alicia de Larocha, Murray Perahia, Andras Schiff and Mozart having small hands, for example.
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