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Pure Data on Raspberry Pi 2 with real-time kernel and Cirrus card?

dmlandrum

I'm aiming to create a Korg Wavedrum-like project. The idea is to have a tensioned drum head miked with two piezo contact mics (one at center and one at edge) feeding into the Cirrus card so the signals can be processed by PD into something more interesting. I'm not talking about just using the piezos as triggers: the audio they capture can be part of the final sound.

 

I know people have said the RPi is not a good platform for DSP, but I think for this application it will be good enough. The problem I'm having right now is with how to set up a real-time kernel on the RPi 2, which is what I'd like to use as it has more RAM and processor power. I've tried Google and the search here, but didn't find anything I understood. Is this possible, and does anyone know where some good information can be found on it? It's been a long time since I've used Linux, so I'm really rusty at the moment.

 

Thank you very much for your help.

  • 0

    Hello Darren,

     

    This post TrainingSphere - 4 - Installing Realtime Raspbian is a well explained how-to for the raspbian installation procedure. I think that it is what you are searching for; in the post there are also the links where you can download the RT distribution.

     

    I have also used a RT raspbian for the use with the Wolfson audio card on the Raspberry PI B+ (but it works fine also on the version 2). You can find information on this alternative in the following post I have published some times ago: Meditech: Microphonic stethoscope This second post is more oriented to the usage and performances of the RT Raspbian with the DSP than the installation method of the RT distro. So I will add something below about the use. If you need more details and information don't exitate asking for details.

     

    RT Image: rpi-linux-rpi-3.18.y

    Where to find it: This point made me crazy as the documentation mentions links that are not available at the date. Is you want to make things simple, I can send you a copy of the image view wetransfer.

     

    Enrico

  • 0 in reply to balearicdynamics

    Thank you much for the information. My Google-fu is normally better than this.

     

    In all honesty, I have yet to buy the parts. I just wanted to make sure I could do what I need with the parts I was planning to buy. It's looking like I should be okay. I also have to figure out how to make the drum part of this project, but that's another story...

  • 0 in reply to dmlandrum

    Hello Darren,

     

    happy to be helpful image Keep us updated on this project, it sounds interesting. There is a "warning" to pay attention to this; as the RT kernel is non-standard, you should be very careful to NOT update / upgrade the operating system as if you advance the kernel features to the last updated components the system goes wrong.

     

    Personally I am interested to the approach you are following as I have a project in queue to make a computer controlled analog synth.

     

    Enrico

  • 0 in reply to balearicdynamics

    Thanks, Enrico! As I learn to use the Element14 features, I'll create this as a project. Right now, I'm just trying to get my feet under me. Also, thanks for the warning. I'm building this to be a standalone embedded project, so it won't be hooked up to the Internet, only occasionally to my local network for me to update certain parts manually.

     

    This whole idea stems from seeing some videos of the Korg Wavedrum (just do a search on Youtube if you're curious) and thinking that I quite like it but it's not quite what I would do with the idea. Korg is using the audio from the head not only to mix in with the synthesized signals, but also analyzing it to determine how the final signal will sound. However, in the end, they're just using it to control a sample playback machine (to be fair, that's not trivial). I want to use the audio from the head more like an impulse input for a synthesis network, but also mixing the straight audio in as well. From there, the sky's the limit, and the synthesis network could be anything, including sample-based.

  • 0

    Ooh, something just occurred to me...

     

    I want to use the new 7" touchscreen as the main interface and display for this project. However, that requires updates to be applied, something I can't do with the RT image, or it'll break. So now it looks like I'm staring down the barrel of doing this the hard way. I was really hoping to avoid that. It's been way too long!

  • 0 in reply to dmlandrum

    Hello Darren,

     

    I had the same problem with some libraries. Then I discovered that it is true that you should not upgrade the sys due the risk to alter the RT components that are a sort of non-standard and unfortunately are not supported by the RT kernel system. But in the meantime, if you can apt-get install components without upgrading the system it continue working fine. So I suggest first to try to install the new components needed by the touch screen display and reduce to the minimum the apt-get install operations, eventually installing manually the needed components the make a test. It is the worth because if the specific parts does not affect the existing kernel and RT involved libraries it continue working fine.

     

    Let me know it this works for you. If not the last chance is to manually install the packages downloading the debs instead of using the apt-get install command. Something that can also be helpful to see exactly what are the dependencies is the aptitude command - similar to the synaptic but more complete and detailed at low level that you can launch from the terminal.

     

    Enrico

  • 0 in reply to balearicdynamics

    Well, at this point, I guess I'll just have to get the parts and see if I can figure it all out. Thank you for your help!

  • 0

    I'm not so sure the Cirrus card will work for me now. It looks like they combined the mic input and audio output together into one connector. I need both available at once. I've tried looking up documentation for what the header pins are connected to, but I can't find anything (the link to the schematic is a 404). Can anyone help me with this? Thank you!

     

    Honestly, it looks like they're not using anything close to the full potential of the chip, unless those header pins let me get at it.