Tags: posts polarity-music OpenSource VST-Plugin Physical-Modeling

Resonarium: Free Open Source Waveguide Synthesizer

Tutorial | Jun 08, 2025

Resonarium is a free, open-source synthesizer focused on waveguide modeling, allowing users to create complex resonator-based sounds with varied exciter and filter options. Currently in alpha at version 0.0.1, it features a straightforward interface but is prone to bugs and heavy CPU usage when using multiple resonators. Users can experiment with impulses, noise, samples, or external audio, and while it has no manual yet, it is powerful for those interested in physical modeling synthesis.

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Short Overview

I checked out Resonarium, a free and open source VST synthesizer that’s still in a very early alpha stage. You’ll find the download links and source code on GitHub, and it runs on a GPL 3.0 license. The synth is based on waveguide modeling and resonators with a feedback approach, which means the sounds can get wild or even screechy, so take care and use a limiter when you try it.

The interface is straightforward if you’re familiar with physical modeling or waveguide synthesis. You can choose between different sound sources like impulse, noise, sequence, samples, or even external audio, then shape the sound through a series of resonators and filters, with options for key tracking, pitch, decay (which is basically feedback), and dispersion. Multiple resonators can run in parallel, cascade, or interlinked modes for more complex sound design, but using many of them can eat a lot of CPU.

There’s also onboard modulation, a matrix for routing, and a post-effects section with filters, chorus, phaser, distortion, delay, compressor, and reverb. Modulation sources like envelopes and LFOs are included, though you might use your DAW’s modulators too. There’s a selection of presets and different exciter types for varied sounds, from plucks to winds. It’s definitely very alpha with some bugs and quirks, but it’s promising, visually nice, and totally free to experiment with.

Introduction to Resonarium

Today I want to introduce you to a free and open-source synthesizer called Resonarium. In Germany, it’s pronounced the same way. This is a very early-stage synthesizer that is entirely open source under the GPL 3.0 license. You can find binaries for Windows and MacOS, or you can download the source code from GitHub and build it yourself for Linux. It’s still in version 0.0.1, so keep in mind that it’s highly experimental and there will be bugs and unexpected behaviors.

First Impressions and Safety Warning

When you first load up Resonarium, you are greeted with a cautionary warning about the unpredictable nature of sounds produced by waveguide modeling. This kind of synthesis can lead to screechy, loud, or uncomfortable output, so there is also a warning dialog in the VST to protect your ears. To be safe, it’s recommended to use a peak limiter set to minus 1 dB after Resonarium in your effects chain. The user interface itself is visually appealing and straightforward if you have some experience with physical modeling or waveguide synthesis.

Key Concepts: Waveguide Synthesis

Resonarium is based on waveguide synthesis, a form of physical modeling synthesis. This technique simulates the behavior of physical resonators, such as strings or tubes, using digital delay lines and filters. The sound begins with an excitation (impulse or noise), which is then fed into a network of resonators that shape the timbre through feedback and filtering.

Sound Sources and Inputs

On the left side of the UI, you can select from several types of sound sources:

Anatomy of a Resonator

Each waveguide tap in Resonarium consists of eight resonators, each with independent controls. These resonators are made up of three filters and numerous parameters:

Some filter settings are somewhat unclear, such as the “mode” parameter on the post-filter, which seems to alter filter type but without clear documentation.

Routing and Advanced Structure

There are several routing options for how these resonators process the sound:

Each waveguide tap can be mixed with the exciter or the previous tap using a mix knob, granting flexibility in building complex, layered patches. The routing of signals can become very intricate, allowing sound designers to craft unique and evolving timbres.

Modulation and Effects

Beneath the main sound engine, you’ll find various modulation sources like envelopes, MIDI-triggered controls, and a modulation matrix. These let you automate or modulate nearly any parameter for dynamic and expressive sounds. Additionally, a post-effects section includes filters, chorus, phaser, distortion, delay, compressor, and reverb, which can be applied either per-voice or globally.

Note on CPU Usage

Resonarium is currently not very CPU-efficient, especially when using multiple resonators or waveguides, so you might need to limit the number of voices or simplify patches to avoid performance issues.

Presets and General Usability

Despite its alpha status, Resonarium includes some example presets to explore. It also supports resizing of the interface and offers helpful tooltips when you hover over various controls, though a full manual is not yet available. Some controls, such as the gain knob, may be buggy or behave unexpectedly. The plugin supports up to 16 voices, though this setting may not always function correctly.

Sound Examples and Practical Tips

Experimenting with the different sound sources reveals a wide sonic palette. The impulse exciter is great for percussive and plucked sounds, while the noise exciter excels at producing wind or brass-like timbres. The sequence exciter is more advanced, suitable for shaping rhythmic or evolving impulses. By carefully combining resonators, filters, and modulation, you can create everything from physical instrument emulations to abstract, evolving textures.

Final Thoughts and Caution

Resonarium is a powerful, promising open-source synthesizer for those interested in waveguide and physical modeling synthesis. However, it is still in alpha, and you should use it with caution. It can be buggy and occasionally unpredictable, both in sound and in stability. Always protect your ears and equipment by using a limiter and low monitoring volumes.

If you are adventurous and willing to deal with early-stage software, Resonarium is worth exploring. You’ll find the download link on GitHub, so try it out, give feedback, and help shape its development.

Conclusion

Resonarium is a compelling new open-source synthesizer powered by waveguide modeling, with a flexible, modular structure and wide sound design potential. It is visually appealing and conceptually straightforward if you have some knowledge of physical modeling synthesis. Expect bugs, high CPU usage, and occasional lack of documentation, but also a great opportunity to delve into unique synthetic sounds. If you have thoughts or suggestions, leave a comment or get involved in the project’s community.

Full Video Transcription

This is what im talking about in this video. The text is transcribed by Whisper, so it might not be perfect. If you find any mistakes, please let me know.
You can also click on the timestamps to jump to the right part of the video, which should be helpful.

Click to expand Transcription

[00:00:00] Yo, folks, welcome back today. It's about this free or open source synthesizer called Resonarium or
[00:00:06] Resonarium how it's pronounced in Germany and it's like I said completely open source synthesizer
[00:00:13] There's a link in the description below to this github page so you can just download here. Maybe the
[00:00:18] binary for
[00:00:21] Windows and Mac OS and maybe you can download the source code and you can build it for yourself on linux
[00:00:29] It's
[00:00:30] The GPL 3.0 license. It looks very good, but it's also very alpha
[00:00:35] But the version here it says it's 0.0.1 so expect a lot of bucks and you know
[00:00:41] Kind of odd behavior
[00:00:43] It also gives you here some kind of caution warning the sounds produced by waveguide modeling can be unpredictable
[00:00:49] So it's basically all based around resonators and feedback and you get sometimes screechy sounds and so on
[00:00:56] So it's in a very early state and it also when you open up here the VST. It gives you a warning protect your ears. I
[00:01:03] Understand I have taken appropriate action. Okay, so we do basically here
[00:01:09] peak limiter
[00:01:11] after the
[00:01:13] device minus 1 dB, okay
[00:01:15] So this is how it looks like in my opinion. It looks very nice and it works very in a very straightforward manner
[00:01:24] So if you know how
[00:01:26] Physical modeling works or waveguide synthesis works. It's basically built upon this concept. So on the left side we have some
[00:01:34] Impulses or sound sources. We have here impulse exciter. You can activate this or we have a noise exciter or sequence exciter
[00:01:43] Or we can use a sample if you want to or we can use external input
[00:01:48] So you can feed in audio signals into this synthesizer
[00:01:51] so here I'm going just for impulse exciter and this one gives us some kind of
[00:01:57] Dirac signal or just a very short burst or even crackle or snap
[00:02:04] I don't know how to call it a very short sound burst and then we feed this into the first waveguide tap here and
[00:02:11] each waveguide tap has eight resonators as you can see here and
[00:02:18] each resonator has different options and is also
[00:02:22] built out of
[00:02:25] one, two, three filters, I would say that's that's the structure and then we go here of course into an
[00:02:33] Post FX section and we have some modulation sources down here. So it's a very straightforward
[00:02:40] Structure of the synthesizer, so let's listen to this here
[00:02:45] So we have now here an impulse and we go into one
[00:02:49] One resonator and we have key track
[00:02:53] We have pitch so we can offset basically the key track or we can disable the key track here and just dial in a Hertz
[00:02:59] Fixed frequency, but we go for for key tracking here and then we have pitch
[00:03:05] So there's a semitones. We can also disable this and then it's basically ratio
[00:03:09] So this is one times the frequency. This is you know two times the frequency and so on
[00:03:15] So two times the frequency is basically one octave higher
[00:03:18] So let's go back to zero here. So this is one resonator
[00:03:21] And then it's here decay and this is more or less like feedback
[00:03:26] So with zero decay, we can basically hear the exciter signal
[00:03:31] You can change the density of the exciting signal
[00:03:35] And of course we can filter this here additionally also with the filter
[00:03:43] So you can go into the first resonator here and we tune up the decay
[00:03:48] This is like a normal just delay with the feedback and then we can dial in here dispersion
[00:03:59] Which is more or less like how frequencies travel
[00:04:02] through the strings
[00:04:04] If you want to call it this way, but it's more or less like the overtones or the tune from the root
[00:04:10] So the overtones are basically yeah offset in a slightly manner
[00:04:24] Then we have a second filter here
[00:04:27] Which is called loop filter
[00:04:30] So you can also key track this or keep here this at the fixed frequency
[00:04:39] So it's basically a low pass filter with the resonance, which is also just feedback
[00:04:44] You can also switch this to a band pass
[00:04:50] And you can also enable here key tracking so then cut off here is not fixed frequencies anymore
[00:05:02] It's just in semitones so we can also offset here this by a certain amount or just keep it at the root position
[00:05:10] So the key tracking is basically when I when you play different notes on the keyboard
[00:05:16] It's the frequency of the filter goes up or down accordingly to the note
[00:05:20] You can already hear it sounds very in tune
[00:05:26] Let's go to 12 maybe here like this
[00:05:42] You get some overtones there and then at the end we have another post filter
[00:05:53] Which can also be key tracked here. There's a cutoff frequency
[00:05:57] There's also resonance, which is the feedback and here
[00:06:02] There's no mode in terms of low pass band pass and high pass here
[00:06:06] It's kind of a number and I'm not sure what exactly does this does
[00:06:11] Maybe you go from a low pass to a high pass over a band pass or maybe it's like a peak
[00:06:18] thing where you just you know
[00:06:22] Do certain type of high pass and you do a resonance at the certain frequency?
[00:06:28] I have no idea what exactly this mode does here
[00:06:31] There's also no description and by the way, you can hover over some of these knobs here and you can see there's an help
[00:06:38] So this is here set the gain of the input signal of the waveguide bank
[00:06:42] And you get some helps here help functions there what everything means
[00:06:51] So, yeah, that's pretty pretty nice to have I don't think there's an Emanuel at the moment
[00:06:56] But like I said, it's an alpha and see this here. It's an alpha and by the way, we can also resize this here
[00:07:03] Do it Lee nice
[00:07:06] So this is the first resonator we can also use multiple resonators with different different settings
[00:07:19] Just mix it in so we have this and this in parallel and
[00:07:22] You can also switch here on the right side from parallel to interlinked and to cascade and interlinked it says here
[00:07:30] It means
[00:07:32] Interlink mode the output of all resonators is fed into the input of each resonator
[00:07:38] so every resonator feeds into every other resonator and
[00:07:43] Yeah, it's like I said, it's just a filter basically then we have cascade and it says here
[00:07:50] The output of the end resonator is fed into the input of the n plus one resonator
[00:07:57] So for me, it sounds like this resonator output goes into this resonator
[00:08:02] And then it goes into this into this into this and this is and so on so it's basically cascade and
[00:08:06] You can filter and filter and filter down until you end up with a nice signal
[00:08:13] also
[00:08:16] Problem I have here with this at the moment is that it uses a lot of CPU when I use multiple of these resonators or waveguides and
[00:08:23] By the way, these settings here also just for one tap
[00:08:28] So you can say here the coupling is cascade and here it's been parallel and then you have here a mix knob
[00:08:35] That says mix between the exciter signal and the previous waveguide
[00:08:40] Which means you can take the output of this waveguide tap and bring it into this tab here and
[00:08:47] You can say at zero we get only the impulse exciter here signal and at 100% or one
[00:08:55] Yeah, it's 100%
[00:08:58] You get not this signal anymore. You get the signal from the waveguide one output tap, okay?
[00:09:06] so you can make it very complicated and
[00:09:10] nested in a way
[00:09:12] Make another one here
[00:09:17] This cascade let's go back to parallel
[00:09:24] Disable this one
[00:09:30] Go to band pass here
[00:09:34] Oh
[00:09:36] Maybe let's go to seven. Oh, what does the wrong thing? Yeah, let's go to seven here
[00:09:52] You have to play around
[00:10:15] So you can play around with this and get different harmonics out of all of these resonators and play around with it
[00:10:39] I don't want to go too deep into this. I'm just playing around for two hours and they end up in so many different places
[00:10:46] We have also here some modulators in there
[00:10:50] Maybe you don't need it in bitwig because you can just attach modulators on the device itself
[00:10:55] But you can also just use here the envelope
[00:11:00] Enable this maybe, you know, just drag it onto this and you can change the strength there
[00:11:06] So
[00:11:08] You can do this we can use an msec one msec two a lot of modulation sources. There's also a matrix down here
[00:11:32] So like I said very straightforward, then we go from the output of these waveguides here straight strict or straight into
[00:11:40] Post fx section. We have filters. We have corals
[00:11:44] phaser distortion delay
[00:11:47] Also time synced here
[00:11:54] Compressor reverb, probably not the best reverb, but you can use it
[00:12:20] Yeah, also a second filter here and some global options pulley fx, it's interesting
[00:12:28] So you have like for every voice or when you play multiple notes
[00:12:31] You have then and post fx for every note separately or just one
[00:12:38] For every of all the notes at once the gain knob has some problems in my opinion
[00:12:48] Yeah, I ran into many issues just using this here when I use multiple resonators for some reason
[00:12:55] We can also reduce the voices here from 16 voices to one voice. I don't know if this actually works
[00:13:00] So, yeah, this is basically the synthesizer
[00:13:04] It it sounds very good it kind of works but there are some bugs here and there and there are also some some nice presets here
[00:13:15] Yeah, I also wanted to show you here the other noise sources. So this is the noise exciter
[00:13:34] This is probably what you want to use if you want to make bad sounds
[00:13:38] So I have like a longer noise type of sound
[00:13:45] And also filter this down
[00:13:47] If you want to make flute sounds or trumpets or stuff like this you probably want to use here the noise exciter
[00:13:54] And we have something like a sequence exciter here
[00:14:08] [Music]
[00:14:37] So you can shape the
[00:14:39] The sound or the impulse here in every kind of way and like I said, you can also use a sample here
[00:14:46] I haven't tried this out yet, but I just want to show you the synthesizer
[00:14:50] Because it's completely free and open source. So why not show it, right?
[00:14:55] But like I said use it with caution. It's in alpha very buggy use it on your own. Yeah
[00:15:03] Be cautious the link is in the description below. Thanks for watching leave a like
[00:15:08] Let me know what you think in the comments down below and I'll see you in the next video. Bye