[Mxsmanic]

What does it mean when the waveform of a sound is essentially symmetrical,
except that the positive excursions of the wave are bigger than the negative
excursions, so that it looks a bit lopsided?

And what does it mean when a wave form looks as though it has been raised or
lowered as a whole, so that what would have been the zero crossings are now
above or below zero?

I've seen both occasionally but I haven't been able to determine what
circumstances cause them.

Someone here said something about trombones not producing symmetrical
waveforms, which reminded me of these anomalies. How or why would a particular
instrument produce a waveform that isn't symmetrical around zero?