Simple question: What are the grey bars in the additive harmonics section of expanse?

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DoctoralHermit
Posts: 77
Joined: 13 Dec 2017

18 Mar 2018

I'm embarrassed to be asking a question that must have a super simple answer, but I couldn't figure it out by reading the manual. In the Expanse RE, what are the grey bars that seem to always be in the additive harmonics section? Are they editable? Thank you!

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Timmy Crowne
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Location: California, United States

18 Mar 2018

Hey DoctoralHermit,

Those gray bars represent the frequencies that are octaves above your fundamental. Filling in those partials will essentially duplicate your waveform at ascending octaves. No worries, I had no idea either when I started with Expanse!


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DoctoralHermit
Posts: 77
Joined: 13 Dec 2017

18 Mar 2018

Thank you! So does that mean when they are greyed out, they are inaudible?

WongoTheSane
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18 Mar 2018

If I may, they're not octaves but frequencies of the harmonic series. It's a bit of a complicated subject, but as simple as I can: imagine a piano string being hit. It vibrates along it's length to produce a sound, at the base frequency; but it also vibrates (to a lesser extent) at half its length; then (to an even lesser extent) at a third of its length, then a fourth, then a fifth, etc. The sum of these frequencies make up the sound. If you analyze each of these frequencies independently, for a base frequency of C, you'll get a C (base) then a C above, then G, C, E, G, Bb, C, D, E, Gb, G, Ab, Bb, B, etc. Actually, it's not exactly those notes because we're using equal temperament and nature isn't, so there is a slight deviation from those notes (for instance, the third frequency is 2 cents above a G, the fifth is 14 cents below an E, etc).

It may be easier to actually visualize what's happening. To do so, try this:

- Reset the device.
- Turn the "Pos" knob fully to the left.
- Check the display: you have one sine.
- Lower the first freq to 0, in the harmonic section, and raise the second one to the max.
- Check the display: you now have exactly two sine in the same period. This frequency is exactly double the previous one (so, it's an octave above).
- Lower the second and raise the third: you now get three sines, so it's vibrating three times as fast as the first one. This correspond to a G, an octave and a half above the starting C. Notice this one sounds ever so slightly sharp.
- Keep doing this: you'll get four sines, five sines (ouch, this one sounds very flat), six sines, etc.

In regards to sound design, it's a valuable tool because those harmonics sound "natural", particularly to reproduce plucked strings, or brass, winds, etc, and they would be really hard to design without. You'll find the exact same system in Jiggery Pokery's JPS Harmonic Synthesizer, inspired by the RMI synth, for instance.

I'm probably going to get killed for oversimplifying this, but if you start with a sine and raise each harmonic in a logarithmic way, you should get pretty close to a saw (similar to a violin sound):

close-enough.PNG
close-enough.PNG (30.24 KiB) Viewed 1046 times
It's a fascinating subject, I'd suggest starting with the Wikipedia page:

https://en.wikipedia.org/wiki/Harmonic_series_(music)

And to answer your second question, yes, they are editable, you can just drag them up and down. What's above the grey line is the volume of the harmonic; what's below is its phase (its starting point). Note that when all bars are at 0, the first harmonic still plays by default. In order to suppress it, at least one other harmonic must be > 0.

Also note that the grey bars are octaves of the base frequency, while the blue bars aren't. It's just a visual help.

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Timmy Crowne
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18 Mar 2018

Correct! They will only be audible if you manually draw white bars over them, upward for amplitude, downward for adjusting phase.


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ravisoni
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Location: Las Vegas

18 Mar 2018

Damn, Wongo, that was a really good explanation! Just begun Expanse, this is helpful!
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WongoTheSane
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18 Mar 2018

ravisoni wrote:
18 Mar 2018
Damn, Wongo, that was a really good explanation! Just begun Expanse, this is helpful!
Thanks ravisoni, glad you liked it! :)

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