Piano is indeed the toughest, and the greatest source of frustration for me
when listening to vinyl which I consider the superior medium in every other
respect. First of all, you may be particularly sensitive to this type of
distortion; not all listeners are. While the turntable is often a major
contributor to the problem, don't assume that the problem is ALWAYS your
turntable; and you should understand a few things:
Piano (and some mallet instruments) is the only instrument on which
vibrato (deliberate pitch variation used by the player for tone color and
expressiveness) is not possible. A struck piano note sounds with absolute
pitch stability; assuming good tuning of the instrument, of course. In the
case of a badly tuned piano the perceived pitch variation is not vibrato, but
instead, audible "beats" in the pitch caused by incorrect tuning
of the multiple strings designated for each note on the instrument. Every
other pitched instrument is generally played with at least some expressive
vibrato, and even when the musician plays it with a "straight"
tone (no vibrato) there is some pitch variation due to the nature of the
physical process involved in playing it. This very slight pitch variation is not
perceived as such, but simply as a contributor to the instrument's unique
sound, and allows for a bit of latitude when judging pitch compared to the
rock-solid stability of piano notes.
As John Gordon points out, even when a piano is "correctly"
tuned, there are artifacts of the tuning process that can cause perceived
pitch variation. Each string of a piano's note will have a different decay
rate. There is a phenomenon that comes into play that is
unique to the piano's decay characteristics: a piano note has two decay
slopes; there is a relatively fast initial decay and then a point at which the
note begins to decay at a considerably slower rate. Additionally, lower
frequencies have much longer decay rates than do higher frequencies on
the piano. If one considers the fact that lower notes on the piano audibly
"excite" higher notes due acoustic interaction and connection to
the same soundboard as a function of harmonic relationships, it is easy to
see how anything less than perfect tuning would cause perceived pitch
instability. Even with ideal tuning there can be some subtle perceived
pitch variation.
Having said all that, other things to consider when trying to judge your
turntable's contribution to the perception of pitch instability are, first and
foremost, the very real possibility that if the music was recorded with
analog tape what you are hearing is partly due to the recorded pitch
instability of the tape recorder itself. But, the bottom line for me has been
that, sadly, only DD turntables offer the kind of pitch stability that I would
consider above criticism. But I say "sadly" because they have
different issues which are the subject of a different discussion.
Dougdeacon, I am intrigued by your comment about the oboe.
