POP: The Programmable Open Pedal



Very cool this project.

With an application to configure the effects would look formidable. Too bad that mod-ui is possibly very costly processing for C.H.I.P

Thanks for sharing the article. I chose C.H.I.P. for POP because of its size and its capability of capturing audio out of the box.It had all I needed and nothing else, and fitted into a stompox pedal that had to contain some other components.

But you are right, processing power is inferior to that of Raspberry PI. Anyway, I’ll give a chance to mod-ui and let you know about the results.

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I am trying to integrate mod-ui in POP pedal. I have seen that with mod-ui (really cool!) I can generate some .ttl files for a pedalboard. But I cannot find the way to load that files in mod-host so the configuration runs without the UI.
My idea is to configure a pedalboard in “maintenance mode”, and then launch that pedalboard without UI, so I give all the C.H.I.P. power to sound processing.

I have browsed the documents but cannot find the way to do it, can anybody please help me?

Thanks in advace,

I have seen a perl script called pedalboard2modhost that could do the trick, where can I find it?

Hi @manolonte!

Currently Zynthian uses MOD-UI to load the pedalboards. It doesn’t use MOD-HOST standalone because we need to get information about the pedalboard (controls, default values, wiring, etc,) and MOD-HOST philosophy is to be as minimal as possible. MOD-UI is the way to go. It’s really lightweight and easy to interface.

The pedalboard2modhost script was removed from source tree, but you can find it in the zynthian-ui repository if you move the pointer to an older revision, by september or so:

Best Regards!


I’ll give a try to mod-ui, I didn’t understand how it integrated with mod-host at first. I have done some tests in my laptop and it seems to work quite well.
Are people at moddevices really happy with using their software?
At least I mentioned their project in my article, because I am already using mod-host:

Thanks a lot!


Hi @manolonte,

In fact this is a problem…
On one hand mod-host and mod-ui are open-source-software. Also the LV2 plugins. On the other hand they are doing a great job and had a great idea of creating and using this software. They need to make money to invent and improve the software. So what to do?

I own a Mod-Duo - and I can only say it it a really nice equipment for musicians! At the moment I think it is more fucused to be an (guitar-)effect pedal than a MIDI-synth (my personal view). As I started to use their software I asked Gian from MOD what they think about this and I showed him a working version of MOD an a Raspi. I think they were not really amused about that - but they also were not surprised about this.

I must say (from my musician view): a MOD-Duo is currently the more stable and stage suitable system. They have a quality management and are focused on stability. You have also a waranty for the soft- and hardware. There are much advantages for musicians.

I think that the open-source-community-users should have the following in mind when using MOD:

  • Think about support of MOD (buying a MOD-Duo, writing/testing LV2 plugins, …)
  • Don’t annoy them with support questions. Also they wrote the software - the support for this should be done from the responsible project! If you want support: buy a MOD-Duo and you get support for the Duo. If the problem don’t occurs on the Duo: try to fix it by yourself!
  • Support by finding bugs (via github)
  • Tell the world that MOD created this software and released it as open-source

Regards, Holger

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Making open source software has that side effect. You have a community contributing and testing your software, but on the other hand, others can use it and modify it for their own purpuses, they have to understand this.

From my side, I’ll promote as much as I can their work, because I think (even if I don’t have a MOD Duo YET) it is a fantastic job, and very valuable for its price. But I am a maker, and I need to design and make a pedal myself. I was about to make that software (mod-host and now mod-ui), but it is already done and available. I think I’ll do a favor to them by using, testing and promoting their software and products. My project is not a commercial one at this moment, if someday it is, I will ask for permission to use mod-host and mod-ui, or will develop my own software (open source, of course :slight_smile:)

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I have been testing mod-ui in my C.H.I.P. based pedal. I have several problems:

  • if I keep my already installed mod-host version, jack ports are misnamed from mod-ui (monitor:in_1 instead of mod-host:monitor-in_1) so it does not work.
  • if I compile and install last version of mod-host, it does not register any jack port ¿?
  • Anyway, I am about to desist and not using mod-ui at all because it is really slow running on C.H.I.P, and one of my goals was not having wireless network at all when playing through the pedal, in order to keep it cooler and having enough CPU to keep latency as low as possible.

I’ll try the other option, having mod-ui (or maybe a home-made gui) generate commands for mod-host.


Hi @manolonte

Yes - this is a special thing with MOD-UI: The MOD-Duo need the output level, so they use a simple software T-fitting named mod-monitor before the output. mod-monitor connects automaticly to the system out ports and provides his ports as monitor-in_*.

You can choose:

  1. Use a jack alias: jack_alias system:playback_1 mod-monitor:in_1; jack_alias system:playback_2 mod-monitor:in_2
  2. Start the program mod-monitor in background - or load it as a jack-module (jack_load mod-monitor)

Ok - that’s strange. You have used jack_lsp for looking which ports exists? (BTW: jack_lsp -a lists all aliases, too).

Using MOD-UI on a PC and than converting/transfering pedalboards? But this maybe no really nice - you don’t hear what you are doing on the web-screen…

Regards, Holger

I’ll try the other option, having mod-ui (or maybe a home-made gui) generate commands for mod-host.

Hi, Manuel.

I am Paulo Mateus. I’ve already contacted you earlier via email. I’m glad you’re making good progress.

If you want to make a lighter version of mod-ui, I would recommend using PluginsManager. I recently posted it on pipy, if you have interest.

I’m doing my version of mod-ui. It’s called apk and you’re using Ionic 3 so you can generate apps for Android, iPhone …

A suggestion in case you want to communicate directly with TCP with the mod-host. You can use android adb to communicate with an Android application via USB. This is an interesting alternative to take advantage of that old cell phone that has been stored for a long time.

I have already written a code for this, maybe it will be useful for you as a source of inspiration


Hi SrMouraSilva,

Have you an .iso image of your system that I could try to use with a Raspberry Zero W?

I’m having troubles starting mod-host… it’s says that no Jack server are available, but I’m sure I’ve started it before!

Thanks in advance,


Hello @maoz !
The Raspberry Pi Zero W just came to my country (Brazil) officialy in this month. Their purchase is on my list.

The error is like this?

Forking... child PID: 13986
Cannot connect to server socket err = No such file or directory
Cannot connect to server request channel
jack server is not running or cannot be started

Did you started the jack with a command line like this?

jackd -R -P70 -t2000 -dalsa -dhw:Series -p256 -n3 -r44100 -s &

A option for start the jack with a UI is using qjackctl for “RASPBIAN any WITH DESKTOP” Operational System.

# Connect to the Raspberry with -X command
ssh -X pi@pi address

# start qjackctl
qjackctl &


Out of curiosity, what audio interface are you using?

Yes, it’s the error I have. I’m using a WM8731 proto board (I2S), and the command I use is:
jackd -P90 -d alsa -dhw:sndrpiproto -p512 -n2 -r44100 -s &

I’ve try also with qjackctl, but I’ve the same problem…

Could you report Jack’s log?

I’ll try this afternoon (GMT +1)… Where I can find the jack’s log? I need to add -V to the command?


By the way I want to restart the entire procedure, 'cause I have installed so many version of Jack (self-compiled, from autostatic repository…) and I don’t know what version I’m actually using… Sorry but I’m a newbie :sweat_smile:

I recommend you to re-burn a new SD card and update several times. After that, you can make a copy of the updated SD card to avoid having to update after re-burn :wink:

I will try to upload an updated image in the next days/weeks.



You are right… By the way there is a very new .iso for raspbian, with all upgraded! :slight_smile:

This afternoon I’ve worked hard, and I’ve re-installed all… now I can start Jackd, mod-host and mod-ui (almost…) without problem !!
There are two big challenge now for me… Understand how to load .lv2 on mod-ui… Have you any ideas??
On the other hand I see two wire connected, one from hardware capture 1 to hardware playback 1, and the second one from hw capture 2 to hw playback 2… but when I try to disconnect one of these wire I read on the log: “Unknown destination port is attempted (dis)connection src_name [system:capture1] dst_name [mod-monitor:in2]”… have you any ideas? probably the name used in mod-ui are different from those used in jackd?

Thanks in advance!!

Edit: It’s possible that I’ve to put the .lv2 compiled in /usr/lib/lv2/ ?? I hope today to have time for try it!

I’ve resolved the problem related to the connection between mod-ui and jackd… but at the moment I can’t load any lv2 on mod-ui! Have you any ideas how to load plugin on mod-ui? where I have to put the .lv2 files?