Understanding FM #3 - Self-modulation, the trick you've been ignoring

If you want to start at the beginning of the series, there's a playlist you can follow: • Understanding Frequenc...
There's a simple little technique just waiting to played with on almost every oscillator -- feeding the output back into the FM input. We'll see what happens in this video.
There is also a second channel video that extends this one, looking at Triangle & Pulse waves, not just the sine wave here. • A bit more self-modula...

[@SousaphoneMusic]

this is the most excited i've been for a youtube series in years

[@SoundVoltage]

Wow, thanks! Glad you're enjoying it.

[@officialphazenoise]

couldn't agree more on this :D

[@super2thesam]

Damnit, I love/hate watching an awesome informative series in the middle of it being made!

[@jamesshawcross3656]

I think this is the best video series on FM synthesis on the internet. Great work!

[@bsbazzman]

oh man never thought to use an oscillator as itself for the modulation. Immediately tried it on Pizza in the external modulation source and immediately got totally diff vibes and it really sang once I combined some other things with it. Hell yea man this series rules

[@Yeebok]

Why the hell is KZbin only just recommending this channel to me? It's like a nerdgasm with catnip on it

[@SoundVoltage]

@Yeebok - That's officially the new tagline for the channel. :) Wow, thanks, I'm glad you're enjoying it. And yeah, KZbin seems reticent to put my content in front of more people. I'll just have to keep working at it.

[@Yeebok]

@@SoundVoltage in all honesty mate I learnt more about FM in the second video than anything else I've watched on here. The video it recommended me was only 5 days old but given your content I'm surprised I haven't seen your stuff before. I'm glad I have now and hopefully this burst of interest gets you some decent rewards for your efforts

[@forestine_]

excellent explanations! great visuals, love the duelling Datas

[@SoundVoltage]

@forestine_ - Thanks! It would be hard to make my videos without the Mordaxes...Mordacies?

[@LeoPerantoni]

You're so good at explaining these things! Im really loving this series!!

[@els1f]

7:26 Wait, there's a second, MORE NERDY channel?!?!😱🤯🔥😱🤯🔥

[@SoundVoltage]

@els1f - Be there *and* be square!

[@FelipeTellez]

loving your series, please more of everything!

[@vutroslavgandic]

Amazing channel, also this topic is interesting as fuck, can't wait for more maths

[@TiniCakes]

thank you!!!!

[@SoundVoltage]

You're welcome!

[@SyntheticFuture]

I had considered doing a series on this topic but I could have never done it this polished. Very insightful, beautifully paced and very clearly explained. This is the go-to reference for this topic 👌🏻

[@SoundVoltage]

@SyntheticFuture - Thanks! It's a big topic, and it took me like a month of trying to finally figure out how to structure it. But at least by then I had a bunch of this written already...

[@SyntheticFuture]

@@SoundVoltage haha yeah. I tried to work it out but all I really accomplished was writing down a giant tree of topics with a lot of question marks on topics where I lacked knowledge. Thanks for taking on this incredible challenge 😄

[@bowel_movement]

I've been messing around with FM for quite a while now, but could never intuitively figure out how to work with it. These videos are so incredibly helpful. I feel like I already understand FM so much better, it's truly inspring. Thanks for putting all of this effort into these videos. It takes a special type of person to be able to dive deep into concepts and explaining them in language that is understandable. I am already looking forward to the next video, keep up the amazing work!

[@nist00]

Love these videos. The structure and examples are super helpful.

[@SoundVoltage]

Thanks, I'm glad they help!

[@diegocano5756]

I love this channel!!

[@lorddulort]

nice consistency!!!!

[@emptycoast420]

all hail Jeff.

[@SoundVoltage]

@emptycoast420 - Finally! Someone gets it.

[@analogueghostmusic]

I'm here for the calc and diffy q's! Really loving this series. Any chance for random Firefly references throughout here too? 👉🏼👈🏼

[@SoundVoltage]

@analogueghostmusic - "My days of not taking you seriously are certainly coming to a middle." :)

[@analogueghostmusic]

@@SoundVoltage ❤

[@GillamtheGreatest]

i feel like this series with its references to previous or future or second channel videos is gonna be like exhausting all dialog options in a bethesda game. unavoidable since FM is weird i think haha.

[@SoundVoltage]

@GillamtheGreatest - Man, I tried really hard to get this into a form where it would fit into a single video with a coherent flow to it, but damn, it just goes everywhere. In the end I had to just admit that I was taking an arrow to the knee and go this route. Thanks for sticking it out. (like the arrow sticking out of my knee...)

[@shey87]

You can achieve the same effect by using a wavetable with a sine and sawtooth wave. Only that the sawtooth would be pitched higher. Right? Loved the series so far! Thank you!

[@modalmixture]

I assume this perhaps cannot be answered without digging into Chowning’s equations, but one thing I’ve always wondered is, why should modulating the pitch create sidebands at all? The distinction between “audio rate” and “lfo” seems arbitrary and dependent on human hearing, so why do the sidebands suddenly appear when the modulator gets into audio rate? Is this where the physics intersects with the phenomenology of human hearing?

[@SoundVoltage]

@modalmixture - You've hit on a question I have spent several hours trying to unwind! This will have to wait for a future video -- but this does give me an idea for something to look at -- but one thing that Chowning does look at is how the appearance of the sidebands is related to Bessel functions, and those are well defined in how they evolve -- it's not just a matter of modulation depth, but also modulating frequency. At certain low values, there just aren't any sidebands. But that's kind of just appealing to the math. Why aren't there sidebands? "Because math." isn't a very compelling answer, but it might be the only real answer in the end. Look for discussion about this in probably episode 5 or 6 :) Thanks!

[@modalmixture]

@@SoundVoltage fascinating. Thanks for your thoughtful responses. I’ve been following along on my OpSix.

[@mooseyard]

Great series! But something is confusing me: i expected self-modulation to be feeding the FM output back into the carrier as its modulator. But what you’re doing is feeding the carrier into the FM circuit twice, I.e. using it as its own modulator. Am I misunderstanding what self-modulation is?

[@SoundVoltage]

@mooseyard - If I am understanding right, I think you're saying the same thing in both cases :) The thing about self-modulation here is that the carrier and modulator are the same thing, so yes, "using it as it's own modulator". But to do that, I am "feeding the FM output back into the carrier as the modulator".

[@mooseyard]

@@SoundVoltage OK, I think I may have gotten confused - you said at the start you were feeding the sine wave output into the linear FM input. I assumed there was a separate modulated output and the sine out would stay a sine. But I guess that’s not the case.

[@user2048]

​@@SoundVoltage Sine out is a confusing name for the output in the diagram at 2:03

[@G.GordonMidi]

Oh man I am not looking forward to when the math comes. 🤞🏼I don’t check out haha

[@jonathanyoung6397]

This is really great but I’m a little unclear as to why when you’re self modulating the additional side bands aren’t symmetrical around the carrier?upwards from the carrier (to the right) the additional harmonics go down in both cases, but to the left it goes up not down when you self modulate (ratio of 1:1). I dont get it :(

[@SoundVoltage]

@jonathanyoung6397 - Well, they kind of are symmetric around the carrier, only the ones on the left (lower sidebands) go down to zero hz and are filtered out, or go to negative frequencies, and wrap around back on top of the positive sidebands. So effectively they 'aren't there', but their effect is still felt.