L vs. XL pianos

[easplund]

What is the actual difference between the L and the XL pianos, in layman's terms? The something is "fully mapped" jargon doesn't mean anything to me.

[NightSkyStudio]

Fully Mapped means there are more recordings (samples) of more piano notes. I don't know what Nord does, but a fully mapped piano would mean there is a recording of each and every note on the piano.

To save memory, the smaller pianos use fewer unique note samples and "stretch" the recording up and down a few semi-tones to account for the "missing" samples.

[analogika]

There is also a difference in the string resonance, which describes how other notes' strings resonate sympathetically when the damper pedal is pressed.

[hector space]

Reading Nord's description it is hard to decide if they mean that it is the string resonance samples that are only fully mapped across the entire keyboard in the XL versions.
Nord's approach to acoustic piano sampling nearly always includes some measure of ambiance from the frame and cabinet. These sound artefacts together with the hammer sounds become what is known as formants in the sample. They are fixed in pitch. So if you use one sample to play several notes you will get an unnatural shift in these fixed artefacts. It has been the practice over the years to remove much of these formants from the samples so you can use one sample for several notes. But this destroys the distinctive character of the instrument. To my ears Nord's sample sets do not do this! They have all the character you could want, even too much at times!