How do i play this?

[healdie]

I have just started studying Schumanns Waltz in A Minor op124 and in Bars 21 and 23 the music directs me to cresendo and diminuendo on one sustained note, how do i do this? as it seems impossible to do on a piano i have experimented witht the soft pedal but the effect is inaudiable, so how do i do it?

[piano_ant]

Is this a hairpin?

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Beethoven does it in his last movement of his Op. 109.

It is of course impossible, but it's meant to help explain the quality, feeling, and dynamics of the notes leading up to and following it more than anything.

The best way to describe it would be to imagine playing the violin and actually forcing that sound from the piano. It obviously was important to Schumann that that note have significance.

[piano_ant]

Oh and on a second note, Schumann had lost his marbles by this point. 

[faulty_damper]

Immediately after striking this note, you gently apply pressure to the key and then gradually release.  For extra expression points, you vibrate your hand to add a naturally warm vibrato.  It really makes it sing this way.  Don't forget to look up and subtly shake your head like it's feeling the resonance.

[slobone]

Watch this clip of a Barenboim master class where he explains how to do a crescendo on a held note: