Harmonic error discussion

[bpb@bpbsn.cca.rockwell.com (Brad Baker)]

Before i bought my Micro-B i called VOCE and asked if it used natural
harmonics or equally-tempered harmonics (as the Hammond B3
approximates) for the drawbar overtone series. Voce told me that the
Micro-B uses natural harmonics for the drawbar overtones. This method,
as has been noted, should produce a beat frequency for certain drawbar
combinations and note choices.

Keyboard Magazine mentioned this (undesireable ?) effect in their review
of the Hammond XB2 and the Roland VK-1000  and stated that both of
these machines do this.  I'm not sure if the CX3 uses natural harmonics
for the tone generation. 

To test if the effect was audible I programed a TX-802 to algorithm
31 to simulate drawbar setting 888800000 and played two notes a fifth
apart.  I could hear the 3rd harmonic of the sub-fundamental (2nd
drawbar) of the lowest note beating with the equally-tempered note
played a fifth scale degree above. Other note combinations and drawbar
settings were worse than this particular combination.

After playing with the TX-802 through a Leslie I decided that I could
live with the difference in tuning for live performance with a module
that weighed substantially less than the real thing.

I received the Micro-B and could hear this artifact. But with the way
i use the thing, this audible characteristic is still just that... an
interesting artifact. I've noticed it only when specifically trying to
hear it.

I'd be interested if you XB-2 owners can hear it. Pull out drawbars 2
and 3 and play a fifth interval.

- Now the flip side of the coin -

A B3 played through a distorting amplifier should produce a similar
kind of effect since the distortion produces natural harmonics. The
natural harmonics of a distorted fundamental will be slightly
different in pitch from the equivalent equally-tempered drawbar
harmonic. Have i heard it? Nope. Prolly too much distortion would be
required.

Regards,

Bradley Baker
bpb@mlb.cca.rockwell.com