Bringing back this old topic because I just come across some new, enlightening information. On page 63 of Mario Igrec's book "Pianos Inside Out", he writes:
The difference in the legato produced by playing staccato with the pedal, and connecting the notes with the fingers, is not merely visual.
He explains in detail, too, with two pages of writing in a section titled "Effects of Touch on Tone". It's too long to reproduce in full here. I will try my best summarize.
He acknowledged the tone from the string can only be varied by hammer speed and acceleration (more on that later). "Still, a distinctly different tone quality can be produced by varying one's touch, even at the same loudness level". And this, he explains, is because of the various noises, both in their loudness and their timing, that contributes, or "fill in", the tone.
The noises includes keyboard noise, and action noise. More importantly, these noises can transmit to the soundboard and get amplified. It can be demonstrated: "keeping the damper pedal depressed, depress a key, hold it loosely depressed at the bottom of its travel, then pound the key with the other hand. The noise is amplified and sustained for several seconds."
Thus, when player vary their touch, by using different part of the finger to press the key, or by changing the starting height of finger to the key surface, or by follow through vs releasing during aftertouch, they vary the loudness and timing of the noise, thus varying the tone.
So back to the original topic of how does playing staccato with sustain pedal depressed different from finger legato?
The pressure after the strike, although it appears to be a waste of energy, actually damps the noise and makes the sound appear slightly warmer.
In action noise, the tone can be affected by hammer acceleration. Although hammer do not accelerate after let off, the manner of acceleration before let off can put different level of flex and twist on the hammer shank. Even when the terminal velocity at which hammer strike the string is the same, a tensioned hammer head and shank can cause sliding at impact and produce a different tone than a relaxed one. He also writes: "Extra-stiff composite shanks, such as those made by Wessell, Nickel, and Gross, reduce hammer sliding and have a cleaner sound during loud playing."
I really enjoyed reading this section, and came away with newly gained admiration of this wonderfully complex acoustic instrument.
