Send it a +/–1v modulation signal, and its pitch would be shifted up to 440 + 500 = 940 Hz, and down to 440 – 500 = …what? Math would tell you -60Hz, but most analog VCOs won’t go below (through) 0Hz, flat-lining at any attempts to drive them lower. Let’s say we turned up the attenuator on our linear FM input to where its range was now 500Hz per volt. It could be, but then you start running into the Through Zero problem. So what’s the downside? Linear FM is often implemented in a way that it does not go as deep as exponential FM. No re-tuning! Even better, it stays in tune while you envelope the modulation depth, so you can create some really cool “plucked” sounds. In our example with a +/–1v modulation signal, the VCO would be shifted up to 540Hz and down to 340Hz, still averaging 440Hz – so it should keep the same pitch (as long as the modulating waveform was perfectly symmetrical*, with no DC offset). Let’s say we turned down the attenuator often found on FM inputs to where its response was 100Hz/V. Linear FM ( starting at 10:03 in the video above) typically uses a separate input for a VCO where its frequency is offset by a certain number of Hertz (instead of octaves) per volt. This problem exists with all forms of frequency modulation, and is why the linear FM input on some oscillators is AC-coupled – to try to remove this offset. This means it will spend more time shifting the pitch of the VCO up rather than down, causing further pitch shifts and errors. * What if the modulation waveform was not perfectly symmetrical? Say it was a pulse wave that was 90% wide, meaning it spent 90% of its time at +1v and 10% of its time at –1v. But if you envelope the modulation depth (a cool effect), the pitch will bend during the envelope. If you keep the modulation voltage level steady, the pitch will remain steady, and you can re-tune the VCO. The problem is, the average between those frequencies is 880 + 220 ÷ 2 = 550 Hz, not 440, so you will get a pitch shift. That means its pitch will go up to 880Hz and down to 220Hz: 1 octave up and down. Say you’ve tuned the VCO to 440Hz, and send it a perfectly symmetrical* modulation waveform that goes + and – 1 volt. through-zero FM (TZFM) stays in tune regardless of modulation depth (as long as you don’t bump up against the tuning limits of the carrier oscillator)Įxponential FM ( starting at 02:06 in the video above) typically uses a 1 volt/ octave input to modulate the frequency of a VCO.linear FM stays in tune for shallow modulation depths (tip: the higher the carrier is tuned, the deeper you can modulate before it starts detuning).exponential FM goes out of tune as soon as you start increasing the modulation depth (fortunately, once you stop changing the depth, it stays in tune).The short answers to the differences between FM types are: Well, modular synths are nothing new, not even in software I ran into Audulus some weeks after learning about the open-source modular synthesis system PureData.(If you’re interested in learning more about the Furthrrrr Generator, click here for an overview of the entire module.) Modular Madness: Building Blocks for Music NerdsĪudulus is a software representation of a modular synthesizer, basically the electronic musician’s Lego: Instead of a monolithic device, you have little bulding blogs you can wire and rewire any way you like. Even though the guy that answers may be some lone code warrior who does all his coding (and his customer service) from a mobile home he’s traveling the world in – you will get help. You may even, after posting some especially ludicrous ideas, find yourself being beta tester for a smart little thing like Audulus. The software is growing up.Įven more brilliant is this: You’ve got some question, or some idea, or some issue, so you go to the developer’s forum and let off steam. Most of the things that drove me mad then just is gone now, and all this in less than a year. But this is the brilliant thing: you can see the software mature. Not too long ago, I wrote a rant about how music software on my iPad didn’t really live up to its promise: the developers tended to get little things like MIDI wrong, apps wouldn’t work together, designs were flawed.
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