Is this possible using the Mozzi library

[feedthe octopus (feed.the.octopus)]

Hello,

since a few weeks I play with the thought of building a hybrid midi 'rompler' using the Mozzi library. But before I start wasting time in trying to code something that works reliable I wanted to ask here if you guys think if my plans are realistic. So my plan is to use 8 bit and 12 bit single cycle waveforms (of synths like Kawai K1 or the Korg DW 8000) and send them through a 24db analog VCF. An arduino would be to underpowered for my plans though I thought that I might want to use a RP2040/2350 board with a MCP4821 DAC for a 12 bit mono output. The synth needs to have at least 8 voices with an oscillator and a simple attack/release envelope generator per voice. I want to use a bit higher audio rate like 65khz but I guess that should be no problem with the mentioned MCU. So what do you guys think? Is it worth ordering some DACs and try it or will not be possible with the mozzi library?

[Staffan Melin]

For this project I would go for the Daisy Seed:
https://electro-smith.com/products/daisy-seed

Its quite cheap, has onboard HIFI DAC (everything you need in a tiny
package), and a lib that is very similar to Mozzi.

You can see some of my projects here:
https://friprogramvarusyndikatet.tv/c/oscillator_maker/videos

Cheers,

Staffan

On 2026-01-13 20:41, 'feedthe octopus (feed.the.octopus)' via

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[feedthe octopus (feed.the.octopus)]

Thanks for your answer Staffan. I thought about the Daisy Seed already, but since I want to make it open source (with gerber files and all) I thought I want to use something like the rp2040 that is available everywhere for cheaper than the daisy. Do you think it will not run on a rp2040 board?

[tomco...@live.fr]

Hi,

8 voices, with only an oscillator each should be no problem at all for an RP2040 running Mozzi. I have already made synths on similar chips (STM32 bluepill, which is single core, but around the same clock speed) with something like 16 voices, 4 osc each, and filters. The DAC might not be the best you could get for your money. RP2040 has native support for I2S (audio) DAC natively, there are a number of chips around there that should provide you 16bits audio for quite cheap (I think people have tried to work with the vs1053, I have been using PT8211 for now).

>  I want to use a bit higher audio rate like 65khz

Support for this in Mozzi is still experimental, the default on this platform is 32k but nothing prevents it in theory.

Good luck with your project!

[feedthe octopus (feed.the.octopus)]

Thank you for the insights! This sounds very promising. I have found a few MCP4822 in my pile of components, but I also ordered some PCM5102 boards already. But I should have mentioned that I am not looking for high fidelity soundwise. And sticking to 32khz shouldn't be a problem. One of my favorite romplers in my rack is the JV 880 and it runs at 32khz too. I don't mind if there is some aliasing if it is not super crazy loud aliasing noise. Do you maybe have some code of your synth you mentioned for me to check out?

[tomco...@live.fr]

For instance: https://github.com/tomcombriat/TES_10-knobs-synth/tree/master (there are a lot of code there, one made for a keyboard with 10 polyphony: https://github.com/tomcombriat/TES_10-knobs-synth/tree/master/10knobs_mono_16bits_PT8211/softwares/XORAND_mk3). Might be of interest for you, there are a few things done for a MCP DAC, for instance: https://github.com/tomcombriat/TES_10-knobs-synth/tree/master/10knobs_mono_24bits_MCP4822/softwares

Note that ALL these codes are done with Mozzi1, and some things might be to be adapted for Mozzi2 (but in the end, should be simpler). Documentation is also, and unfortunately out of date.

For aliasing, there are ways around it, for instance using the MetaOscil class (https://github.com/sensorium/Mozzi/tree/master/examples/06.Synthesis/NonAlias_MetaOscil).

Hope this helps!

Best,

[feedthe octopus (feed.the.octopus)]

Thanks alot! I will have a look at it on the weekend. 

[Martin Gerken]

Hmm... Let's not forget that we need 8x ADSR curves for the (digitally implemented?) VCA and 8 ADSR curves+DACs for the analog VCF. I'd love to see the circuit! Maybe look at the Shruthi-1.
Best. Martin

[feedthe octopus (feed.the.octopus)]

I don't know why, but it keeps deleting my posts right after posting it... Maybe because of the URL

Sorry I haven't explained it more precise. It will be paraphonic with a simple envelope generator for each oscillator voice. The DAC output will feed into a singe VCF and then into a final VCA. The VCF is roughly based on a Roland 703e filter and will look something like this: see post below!

The VCF will have it's own analog ADSR and LFO.

[feedthe octopus (feed.the.octopus)]

Here is the VCF: https://tinyurl.com/22ywuten