An app for additive synthesis with sine waves? Or a virtual DX7?

Hi

You could take a look at FM8 from Native Instruments

CCT

Well, this is really kludgy and labor-intensive, but presumably you could create any number of software tracks with sine waves at the fundamental and all other desired frequencies (using almost any synthesizer for each track) until you get the tone desired - this would be essentially a gigantic chord - then combine them into one audio track, and repeat, scaling the frequencies, and then create an EXS24 instrument from the audio tracks. For a given fundamental tone and all other frequencies (overtones only?), by converting the individual tracks to audio tracks, I believe (Ibut not positive) that you could even adjust the relative phases of each tone.

I don't know whether this may be of help, its something I remember seeing a while ago (there's a second part to the article still available) -

http://audio.tutsplus.com/tutorials/sound-design/an-introduction-to-self-oscilla tion-and-fm-synthesis/?search_index=10

+1 FM8 from NI...

Yeah, FM8 is a great synth of that type and can certainly be good as a virtual DX7, I'm not entirely sure what Mike is getting at, but I think its a way of explaining about the way that different frequencies combine to create the particular character of, well, initially a synth sound (all sounds in nature are built in the same way, ultimately), hence the reference.