It's a simple multiplication.. there's nothing special to it. If it's 0.5 in one (image or envelope) and 0.1 in the other, then it's 0.05.

And when the timbre single cycle partials all are 1.0 ( adjustable with the ENV, right?), the sound is fully calculated be the IMG partial resynthesis?

yes

So partials common to both the Timbre wave and the IMG wave will be multiplied in amplitude, partials in the IMG wave but not in the Timbre wave will not sound at all (because they are multiplied by the 0 partial in the Timbre wave), and partials in the Timbre wave but not in the IMG wave will not sound at all (because they are multiplied by the 0 partial in the IMG wave)?

In other words, only those partials that are common to both the Timbre wave and the IMG wave will sound?

yes

see presets->image synthesis->gate
it's a simple 2-pixels wide bitmap (even if it doesn't look like, because displayed with interpolation), that acts as a gate.

(& you can change the interpolation method, with "block" it will be a pure gate, while with "linear" it will be all smooth)

Thank you.

Is there an easy way (as TabSel seems to suggest) to raise all of the remaining partials in the IMG wave to 1? Would this result in all of the existing partials in the Timbre wave to sound at their original amplitude (as they would be multiplied by 1), the partials common to both the Timbre and IMG waves multiplied, and none of the non-common partials in the IMG file sounding?

yes, you'd edit the image, select "all" planes (from the menu, it's gonna launch Paint or whatever you have installed), resize the image, fill with 100% green (amplitude) & 50% blue (sub-freq), and paste back in Harmor
http://www.youtube.com/watch?v=iqMgjeUXFe4

Thank you.

Another quick question, if anyone is still following this. I know that additive synthesis in general uses sine waves to build up to the ultimate waveform. The two waveforms in Harmor's timbre section, though, are a sawtooth and a square wave. Does Harmor generally not use sine waves, but whatever waveform is in the timbre section to build up to the ultimate waveform? What about resynthesizing a sample - are sine waves not used here, either? Thanks!

I'm sure in additive it's always sine waves.
There's just no other waveform that is as pure as sine. Sinewaves have no overtones and one wants to control each harmonic of the resulting wave so it has to be built up sith sines.

I'm really confused - why would neither of the two Timbre waveforms in Harmor be sine waves, then?

Harmor builds those timbres.. out of sine partials. When you click those timbre displays you get to the mapping where you can control each of the overtones.

OK - that makes sense. One question, then - when you import a sample for resynthesis, is it always multipied by the Timbre waveforms? In other words, does importing your own sample using the resynthesis template lead to the best resynthesis, or do you first need to adjust the partials of the Timbre waveforms to 1 as mentioned above (so as to prevent application of the saw/square waveforms of the Timbre)?

All you have to do is drag&drop a sample. But you can load the "resynthesis" perset first, which sets more suitable image parameters.

But is every sample you drag and drop for resynthesis automatically combined with the Timbre waveforms? If so, would the resynthesis be even better if the Timbre waveforms are set to something other than the saw and square waves they are on by default?