[Peter Larsen[_3_]]

Neil Gould wrote:

Scott Dorsey wrote:

What makes you think so? The waveform not be centered around zero
all the time, sometimes that's just the way the waveform is.

Take every sample, sum them all together... and you won't necessarily
get zero either.

Well... this is an interesting thought exercise, if nothing else. I
would think DC offset would be represented either as a steady-state
level above or below zero when no AM is present or as an asymmetrical
waveform. If so, perhaps DAW software "removes" DC offset in the
absence of a steady-state level by re-centering the waveform based on
an average of the waveform values, and that creates an opportunity
for error, especially for asymmetric waveforms lacking DC offsets.

Re-centering would be an error. The mechanism is that the unlinearity of air
causes 2 harmonic distortion and second harmonic distortion causes
asymmetry. The asymmetry is in itself audible as an ""intonation or
chord-weight change"": take a recording of asymmetric vox humana or trumpet
and invert it and do something untraditional: listen! - or take a recording
of a speaker with varying asymmetry and listen for the difference in
perceived voice tonality with difference in asymmetry.

The asymmetry is "known and described in the literature" and it is an
established practice, at least for those that run AM receivers, to insert a
contraption in the audio chain that watches signal asymmetry and inverts
signal polarity to maintain positive asymmetry for optimum transmitter
modulation. The Elton John and Kiki Dee duet was bad news for those systems
.... one singer on each side on a fig 8, my recollection of Studio Sound is
that it was an AKG "the everchanging model".

What is less easily agreed on is that some, myself included, feel that
getting the overall polarity right is important for imaging and perspective.
Interestingly however it appears that just as some types of microphones are
more likely to deliver asymmetric audio than others also the audibility of
it varies with amount of second harmonic distortion added by the playback
transducers.

My observations - I do NOT want to call them "findings" - are that high
quality omni microphones tend to deliver recordings that are more symmetric
than some cardioids, applause does however always seem to have positive
asymmetry, also high pass filtering in post and/or the use of multiband
processing does tend to de-naturalize the waveform and can cause the
polarity to appear inverted.

Kind regards

Peter Larsen