Harmonization

jungledmnc wrote:
> Hey guys thanks a lot. Anyway I know something about harmony, so that's not
> the issue here. The problem is how to "harmonize" an arbitrary sound - add
> some more frequency content, so the sound "sounds" different (more "full"
> if possible). I thought that simplification into octaves should ease the
> problem.
..
> Ok, let's say a simplify the problem even more into a single note. Then it
> will be X Hz and I want to add 2X Hz just as you said. But how to do that
> without DFT? The first idea presented here was to interpolate the block
> into a half-long block and double it. But how to make it connected? The
> fact that the note is X Hz does not mean, that there is not an additional
> frequency content above it, which I also want to move by an octave. And
> what if I want to use it on any signal - I mean more notes or some
> arbitrary noise-based sounds like drums or even a complete mix?
> 

This is different again, and not what musicians call "harmonizing". It 
sounds closer to what is called "exciting", after the Aphex "Aural 
Exciter" effect that dates back to 1975 or so. It added small amounts of 
(somehow) synthesized higher harmonics in order to brighten up the 
sound. The method is patented, and was claimed at the time to have been 
discovered by accident when an engineer incorrectly wired up a circuit. See

http://en.wikipedia.org/wiki/Aphex_Systems

So it is closer to a general waveshaping method than to anything 
involving explicit pitch shifting. To add harmonics (= distortion, 
albeit very controlled) you need some sort of non-linear transfer 
function. The Aphex effect adds some phase shift and compression as 
well, and is level dependent.  To clone it would almost certainly 
require some sophisticated dsp (e.g. analog modelling).

It is not something I have ever done, so cannot advise on how to create 
the effect. It would be well worth asking on the musicdsp list, as there 
will very likely be folk there who have done it more than once. A 
frequency-domain (e.g. pvoc-based) approach could well prove a good 
route to an at least plausibly similar effect. I have indeed added an 
octave pitch shift to a flute recording to get a sort of enhancement 
effect, but note that this shifts everything, including fundamentals, so 
it is much more like adding a 4ft organ stop (or simply doubling flute 
with piccolo!) than an "exciter" effect.

NB: to make a sound more "full"  (in the vague way musicians define it), 
the standard method is to use conventional EQ to boost the signal in the 
(vaguely) 1KHz to 2KHz region. Might be lower range for drums, etc.


Richard Dobson