Hello,
I want to build a hardware device running on pd but I just don't know how to physically bridge the gap between hardware and software. I'm not even sure what kind of hardware I need, or how to map pd's inputs and outputs onto physical inputs and outputs.

For example, if I wanted to make the most basic patch, where I just send three inputs straight into three outputs with a 100Hz hi-pass in between, how would I go about putting that into a hardware device that I could use away from my PC? and what kind of hardware would be most suitable for making a real-time audio processor (similar style to a guitar effects pedal)?

Sorry if this is really basic, I'm kinda new to this.
Thanks,
Dan

I've been using the Odroid to create a modular synthesizer programmed in Pd and Arduino. I've finally made it but haven't made documentation yet, it will come in the next month or so.
Another option is of course the very popular Raspberry Pi. You'll need an external sound card to get Pd's audio outputs into the real world. If your sound card has at least three inputs and outputs (which is not the most common thing, IMHO) then you're probably good to go. Otherwise you'll have to implement some sort of physical patching that can be translated into Pd language. One good example is the rePatcher by Open Music Labs. This is what I based my synthesizer on and turned it into a modular synth.

Depending on what you want to do there can be different approaches, but I would recommend starting off with a Raspberry Pi and an Arduino.

Ok, I've been looking into Raspberry Pi, Arduino and Odroid today, though my lack of hardware understanding is still leaving me a bit confused. However, from what I gather, Arduino is simply not capable of processing high quality audio (9.6kHz sample rate at best). Maybe I'm just reading things wrong. In any case, I'm looking for 24 bit, 44.1 or 48kHz sample rate audio processing.

If I use the Raspberry Pi or Odroid as the main processor, I'm still going to need analogue inputs because I want to process audio from actual instruments, as opposed to synthesising. From what I understand, I'll need to buy a 1/4" jack as the input, connect it to something like this http://www.ti.com/product/PCM1803A/description and then somehow connect that to Rasperry Pi/Odroid. Then do basically the same thing backwards with a DAC instead of ADC for the outputs. Is that the right way of looking at this? Am I overlooking anything?

@Lemon £uk 30 will buy you (on ebay...... there is one without bids 53 minutes left) a windows 7 laptop, with screen, keyboard, power supply, trackpad and a 320Gb hard drive.

You will spend more than £30 on a basic computer (raspberry Pi.....)......... when I say basic, I mean without a power supply, keyboard, screen or trackpad.
And if you are not familiar with Linux you will have some extra learning to do, and you will need to learn how to communicate with your small computer that has no screen.

If size and weight are important for your project you will find a lot of help on this forum with all types of computer
I would recommend learning about Pure Data, following some tutorials, and building your patch(s) on your laptop while at the same time you gather as much info about the options as you can..... before you decide.

A Pd patch will run on Linux, osx, and windows so you can just load it up on the small computer of your choice when (or if) you decide to buy one.

For 3 audio inputs or more you will need an external soundcard...... and there is a huge range at reasonable prices that will work with windows 7. You will need to research which ones will work well with the Pi and others.

David.

Apologies if this is totally outside what you're looking for, but have you seen the Axoloti Core board?

http://www.axoloti.com/product/axoloti-core/

It doesn't run Pd but it has 1/4" jacks and uses visual patching software that might have an easier learning curve, if you already know Pd.

There's also the Teensy family of Arduino-like boards, which have an audio board available and another visual patcher:

https://www.pjrc.com/store/teensy3_audio.html

I'm also hoping to build a Pd-based desktop synth. From my research so far, a Raspberry Pi 3 + some kind of Arduino (or a Teensy) seem to be the best bets in terms of support and documentation. Although as David says, they won't be as cheap as a secondhand laptop.

@whale-av yeah, being a portable effects processor for instruments, it needs to be very small and self-contained (in the sense that no peripherals should be sticking out like keyboards or audio interfaces) which is why I was wondering about implementing adc and dac with physical inputs and outputs into the actual thing instead of using peripherals.

@bmd the Axoloti core looks like pretty much exactly what I was going for with hardware! Although missing an extra input and output. That said, I plan on dealing with two mono signals so perhaps I could use the single stereo input and then separate left and right into input 1 and input 2... Having a quick look at this though http://www.axoloti.com/axoloti-patcher/ suggests that it isn't as versatile as Puredata with not many objects available but maybe I'm wrong again. Definitely going to research more into this. It also sounds like it has an easier solution to my problem of not knowing how to physically implement my patch onto some hardware. Thanks for showing me that.

Seeing as Raspberry Pi/Arduino/Puredata has a lot more support around it, plus the fact I wouldn't have to learn a whole new programming software for Axoloti, do you think I'd be able to make something very similar to the Axoloti Core using a Rasperry Pi? Or is this just overcomplicating things to the point where I might as well just learn how to use Axoloti? I'm struggling to find any appropiate ADC for the Raspberry Pi, but I'm sure there's got to be something high quality around, I mean, I find it hard to believe nobody has made a Raspberry Pi with at least 16 bit 44,1kHz audio input and output.

Also, @whale-av made me think... If I'm not having any peripherals sticking out of my signal processor, a touchscreen might be a reasonable idea for this to simplify things and not take up space. It looks a lot more difficult to do this on Axoloti than Raspberry Pi who have their own touchscreens conveniently available, or the Odroid @alexandros mentioned which has a HDMI port. A touchscreen might not be totally necessary but now I've considered it I kinda want it.

A decent ADC for the Pi is indeed something pretty hard to find. I've been using a Focusrite Scarlett 2i4 which I've ripped off its case and put it in my project's housing, and it works fine. This requires some hardware hacking though as you'll might need to remove some parts from the sound card's circuit board (like potentiometers) in order to bring them to the desired position in your setup.

@Lemon Just a thought...
I run a complete monitor mix in my laptop with Pure Data.
When I am travelling / working away I always have my laptop with me anyway, so why not? Maybe you do too?
It is win7, and I use a motu usb card with 32 inputs and 22 outputs..... which is too much for you of course...... and it allows the musicians to be completely wireless on stage (they have wireless packs and wireless in-ear).
They control their mix from their phones, or I provide tablets..... and we have used the system when accompanied by orchestras as well, to control all of the monitors.

The point....
You could run your laptop at the side of stage, as I do, and control everything from your phone using Osc over wi-fi... if you were thinking of a touch screen anyway.
The only problem I can think of straight away would be a "stomp" switch if you need one, although that could be analogue before the signal is sent off to the soundcard.....
You would have a greater choice of soundcard as well.......
David.

@lemon I thought of one other device that might fit your requirements, the Hoxton OWL pedal:

http://www.rebeltech.org/products/owl-pedal/

The hardware is open source.

You might also like this page on the Axoloti site where the designer compares his board to other products - useful starting point for research:

http://www.axoloti.com/more-info/comparing-axoloti/