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Making a Basic Additive Synth in Logic


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Hi guys,



Today I’ll show you how to make a simple additive synthesizer that can make some really crazy sounds.


The Fourier Theorem states that every sound can be split up into individual sine waves. Additive synthesizers make use of this by placing sine waves (called “partials”) in their correct harmonic places. Different sounds create sound with different harmonics, but the math is (almost) always the same. A sawtooth wave has every harmonic lined up in a row, a square wave has only odd harmonics, and other waves have different assortments. With additive synthesis you control which harmonics you hear.


We will make it with 6 instances of the EFM1. Since we are making the synthesizer by synthesizing each partial with a separate synthesizer on a separate track, we can do some things that you can’t in things like Razor or Harmor (of course, Razor and Harmor can do things that we can’t with this little home made one). It’s been surprisingly CPU effective with 6 partials, but the one I made with 10 partials was not, plus it was a pain in the @ss to control effectively.




First off, make your first instance of the EFM1— don’t make all of them quite yet!





Now, once you’ve done that, open up your EFM1 and initialize it. All you need to do to have it work is have every modulation off, your FM at 0 and your ratio at 1:1 (it is important that it is not 1: 0, as this will create no sine wave. (Change your volume envelope NOW if you want to; it’ll be a pain to change later)






Now create 5 more EFM1s by duplicating your first track.






Now is when it’s important to use the EFM1 instead of a simpler synth that can only produce a sine wave. Set your carrier oscillator harmonic to its rightful place (2nd instance of EFM1 should be set to 2, 3rd instance to 3, and so on). Luckily, harmonic ratios are the same as FM ratios! This makes the EFM1 perfect for this job; it can produce a sine wave, and has control over the harmonic of that sine wave.







Once you’ve done that, you’re only one step away from the base of your synthesizer. Just put them in a summing stack and you can play MIDI info through all of them; they should all play at their correct harmonic. It should sound similar to an organ (the Hammond Organ is, in fact, an additive synth. it creates its individual harmonics by spinning metal plates). I suggest compressing really hard and lowering the gain, 6 synths together get quite unruly, especially if you’re playing polyphonically.







The basic synth is done (we’re not done yet though)! With a MIDI track on the summing stack you play all EFM1s at once. (In Logic 9 or earlier, I believe you would have to have separate regions for every track)







To get some really warm distortion, distort your even harmonics, especially your 2nd partial (I distort my 2nd and 4th). This makes lots of even harmonics, which leaves a warm, saturated sound.








Here’s my favorite trick in this synth, and usually the only reason I would make my own additive synthesizer. Go to your automation (preferably on a distorted partial) and select “Carrier Harmonic”.







Now automate it around gently. It sounds best in the lower harmonics, my modulation usually goes from 1 to 6 or even lower, never higher (unless its distorted and I want it to bite). It also usually only sounds good if the automation has a very simple pattern. You automate multiple partials to get crazy effects, but its hard to get it to sound good unless they’re running parallel in partials that are relatively close to each other.







Here’s another trick. With a few of your partials, especially the 1st, add an FM transient with the modulation envelope. This adds a lot of bite to your sound.





Another thing that can blow your mind is turning up the FM and changing the modulator wave on some of the partials (especially the 3rd). If you do this right you can make really big sounds. Detuning individual partials can also make big sounds and sound really good. Panning individual partials (generally not the 1st partial) in opposite directions can make sounds really, really wide without changing the actual timbre of the sound. If you want a filter you can add one to your summing stack. you can also add effects to any of your individual partials, which can sound really fantastic sometimes, even if they are just sine waves. Changing the amplitude of partials is the standard thing to do for additive synths, but with 6 partials you can't do that much.




If you have any questions post them here and I should answer unless I’m off saving Gotham from the Joker again (what a pain).



I hope you guys make some crazy sounds with your new additive synth!




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Thank You for this! I was able to make some amazing sounds using this trick. What I really like about this, Is you have endless possibilities to tweak your sound sets. e.g. I put a ring modulator on the 6th harmonic and it was beautiful. :-) BTW, can you do this on any other Logic synth or is the EFM1 the only one? Thx!
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Ring modulation is a great idea! I've gotta try that one. You could do it with other synths, but EFM1 is great because it has easy partial control and uses a relatively low amount of CPU. You could, however, do this in other synths if you would like. For example, in the ES2 you could set one oscillator to -12s, second to 0s, third to +7s, and continue up the partials with other instances of the ES2 (you can look up the placements of harmonics online). This way you have more control over the oscillators interacting and modulations, but you don't have quite as much control over each individual partial, which is fine depending on what sound you want. These types of manual additive synths are really good for experimenting; it's easy to make stuff that no one has ever heard before. (One more thing to keep in mind if you make these with something like the ES2, when you look up the increments of harmonics, search for cent increments in just intonation. If you can't find this, post something here and I'll figure them out for you).
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