Playing with 4Pockets Harmonic Exciter -- Technical question:

OscarSouth

I had a good play around with the Harmonic Exciter this morning, running a sine wave through it and into apeFilter while manipulating just about every moving part of the Exciter in as many combinations as I could think of. Got a good feel for it now but there was one thing I wasn't sure of, so if anyone has some insight then please share it!:

It seems obvious that the different bands are the ascending order overtones of the harmonic series, though I'm not really sure what the difference between lifting the fader (towards +64) and dropping it (towards -64) has, on a technical level. It seems to affect the same overtone (which is logical) but the sound is definitely different depending on which way you go -- definite timbral differences seems to change the proportionate strength of the fundamental in different ways.

I thought that maybe it's something to do with phase or something like that, but I'm not sure. Does anyone have any accurate info about this?

Cheers,
Oscar

LinearLineman

Haven't a clue, Oscar, but I think @McD would be interested in this.

CracklePot

Nothing accurate, but logically thinking, it would be a boost/cut control for a specific harmonic. So you could boost it, which seems like what you expect, but can also suppress it, if that gives you more desirable results.

OscarSouth

@CracklePot said:
Nothing accurate, but logically thinking, it would be a boost/cut control for a specific harmonic. So you could boost it, which seems like what you expect, but can also suppress it, if that gives you more desirable results.

I don’t think so, I would have assumed that too but raising or lowering still adds the overtone (audible and very clearly visible on apeFilter), however the timbral quality and proportionate loudness of the fundamental differs.

LinearLineman

What's the dev say?

cian

It definitely adds overtones. I think they do it through a combination of altering the phase and distorting the signal. But I'm not 100% sure. So I think they change the signal in such a way that harmonics are added (but there are also other effects)

CracklePot

I checked the faders’ effect on some simple oscillator signals, and they do different things based on the input signal. Sometimes they boost/cut like I mentioned, sometimes they boost both ways, sometimes they do an inverted boost/cut, sometimes they don’t seem to do hardly anything.

And to make it harder to understand, the graph display doesn’t seem to reflect what is happening very accurately. I got different, and seemingly more accurate feedback from the apeMatrix oscilloscope.

Until someone can explain this weirdness, I will carry on adjusting this by ear primarily. But now I will apply the fader adjustments more liberally since I can’t predict what position is going to sound good.

McD

This is a cool App. You won't be boosting a existing frequency like an EQ does.
You are generating a new sine wave of that's an integer multiple of the detected root
frequency.

To literally go negative it seems to be acting as an EQ which is likely. But it's possible to
use positive and negative sines with respect to the fundamental. I wonder it this is the basis
for EQ algorhytms to use extra plus of negative synthetic waveforms.

I have enough Engineering training to understand that any wave form can be created by
combinations of "overtones". A pure sine wave has no overtones. Just a sine wave of root the frequency.

Over tones are:
2
3
4
5
6
7
...
times the root frequency.

So, when I play with Harmonic Exciter I try to think:
1 is an octave up
2 is octave + 5th
3 is 2 octaves
4 is 2 octaves + major 3rd
5 is 2 octaves + 5th
6 (this is a gem) is 2 octaves and a minor 7th (usually just called the 7th)
7 3 octaves
8 3 octaves major 2nd (i think)

These are the notes a bugle can can. Trumpets are bugles with extra plumbing to drop it by
6 1/3 steps to cover all chromatic possibilities.

Those sliders on Hammond Organs are drawbars for extra overtones to be added to the fundamental of any note played. Pipe organs of course started this. Making a pipe organ play in tune in any key is impossible... thanks math. They say music is math but it's full of rounding errors. But computers can do the right thing anyway. Air in a pipe cannot.

I was hoping folks would start discussing the Harmonic Exciter because I found it to be very subtle and the overtones are not in your face like on a B3. I expect an injection of a discernible pitch but it appears to be using a lot of EQ techniques. Probably based upon the
electronics in the classic studio "Harmonic Exciters" and not what I think it would mean like the B3 Drawbars.

Someone with studio chops will set the record straight since my view is based on that
acoustics theory and the Fourier Series. I'll bet Khan Academy has some details on one or more of those topics. Not that most would care.

(Cut and paste to the "Knowledge Base". The @LinearLineman is on a mission and has
moderator authority to manage it. I fear his wrath so I'm going to act accordingly... insult him in very subtle ways. I have this thing about authorities. Fight the man.)

cian

Actually I'm fairly sure it's using Chebyshev polynomials - which are a special kind of waveshaper that add harmonics.

Definitely not EQ.

McD

Duh. (Thanks for knowing this... I love the details for about 45 seconds.)

aquasloth

@McD said:

Duh. (Thanks for knowing this... I love the details for about 45 seconds.)

Well, now you're just making shit up.