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Alchemy: FM question


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Hi, looking to better understand how FM works in alchemy.


Particularly how the parallel and series filter routing affects the modulator/carrier signal flow.


Here's a screenshot of what I think is happening. Is this correct?






Or is there a kind of 'virtual' source duplicated for each filter?

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I'm not 100% sure, but your image makes sense to me. I would guess that's how it works. In parallel the first modulator would affect the carrier, then the second modulator would affect the already affected carrier and the 3rd would be the same thing. In series, I guess maybe the 1st modulates the second and then the combination of them will affect the 3rd and those 3 combined would affect the carrier. 
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I was just trying and Series really produce more audible effects even with the Freq on all 3 being the same, unlike the Parallel where the effects are only more audible when all 3 filters have different frequencies. I guess it really depends on what you're trying to achieve. I believe this follows the same principle of FM8 from Native Instruments where a Modulator can modulate itself or another modulator.
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I'm assuming you downloaded 3ple's great template from this thread?: https://www.logicprohelp.com/viewtopic.php?f=8&t=132304


Technically, Alchemy doesn't do (digital) FM synthesis in a traditional sense.

3ple's template shows a hybrid technique that incorporates some FM-like elements / filter features to create a pseudo-FM synth. This is more akin to the FM synthesis of analog synthesizers, than the FM synthesis of Yamaha's DX synths.

Alchemy is limited by the fact that it's only the self-resonating filters that are used to modulate the sine wave (carrier) - or output signal of the preceding filter - when doing this type of FM synthesis.


Ideally - and hopefully this will be incorporated in Alchemy at some stage - you would be able to use the Additive analysis method (or simply draw in) to create an ADD "waveform" source (the carrier). This would need to generate an interpolated representation of the source material (a series of partials in the ADD editor, set to the same amplitude, but with different phase and tune values - which the editor already offers).

You would then perform a second analysis - or do both in one analysis step (or draw in) - to create a second ADD source (the modulator)...and use this to cross-mod the carrier frequency. As above, an interpolated representation would be created.

Alchemy can perform similar types of cross-mod/synthesis now, but not in a "pure" digital FM sense.

As examples of where you could experiment with other FM techniques:

- modulate oscillator pitch/frequency (or filter frequency/res, etc.) with any of the bazillion mod options, so you can approximate carrier waveform modulation in this way as well....but again, not as you could with full-on digital FM synthesis.

- envelope control of each harmonic partial available in the ADD editor, which again can approximate features found in the Synclavier FM engine, for example.

These, and other methods, won't necessarily lead to typically "FM" sounds, but can certainly yield interesting results.


Ultimately, if the Alchemy team implement something that allowed full cross-mod of partial timbres with other partial timbres (using just sine waves), they'd have the uber-FM synth (not that you'd need them...but up to 512 partials for each, with individual envelope control per partial!!!! (for the masochists and anally retentive) - way more than the Synclavier's 24, which only offered a single envelope for ALL modulator partials)....and on top of that, being able to perform this type of thing with more complex waveforms would make it very easy to do DX-style sounds.

In the meantime, you can experiment with Alchemy's FM-like features, but if you're more interested in getting "DX" sounds or simply getting a handle on how digital FM works, the EFM-1 and Retro Synth are the first place to look.

Having said this...and although the approach is massively different, Alchemy's ADD synth engine is very powerful and can readily generate a number of "classic FM" sounds.

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Thanks for your thoughts @3ple and @oscwilde


I’m not after a specific sound but was getting a little confused when making sounds from scratch. I have a habit of reaching for FM as shortcut to get somewhere quickly and started to wonder about the implementation. Especially when in series - the way the freq knob also seems to act as a cutoff for the preceding signal. But your explanations make sense.


Very interesting read @oscwilde. What you describe would be incredible. I’d settle to be able to modulate one VA source with another VA source. But as you say there are endless ways to arrive at  fm-y and other interesting timbres.


A little modulation of freq/mod/feedback knobs opens things right up. It’s kind of possible to emulate the way FM8 has seperate envelopes for each operator. The modulation + the additional waves result in sounds I haven’t made in FM8 before, even with the limited implementation.


Yes I must admit I haven’t gone too deep on the additive engine yet. I had an a-ha moment the other day when I realised each partial can have it’s own envelope. With only a few partials a lot is possible.


I've not downloaded @3ple FM template but will make sure I do!

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