Slightly inharmonic piano partials create the instrument’s characteristic timbre

Evidence

It is not at all clear that stretched partials are a bad thing musically. The mildly out-of-tune partials give the piano part of its characteristic color, and any synthesizer that leaves out the effect winds up sounding rather dull and unreal. Of course, this is a matter of habituation; there is no right or wrong here. — Eric J. Heller, Why You Hear What You Hear- An…, 1821

Categorization

• XREF: Ties to the reader’s audio/synthesis interests — explains why simplistic synthesized pianos sound fake.
• SHARE: Worth sending to anyone who builds synthesizers or samples pianos: the reason naive synthesis sounds dull is missing stretched partials.