First step: a Raspberry Pi 3 screwed on to a 7" touchscreen. Using a version 3 here rather than the new version 4 because the 4 has micro-HDMI output, and I don't have a micro-HDMI cable to hand.
Next, plug everything together. A total rat's nest. Note that the sound card (top right) is at a bit of a funny angle. It works fine despite that, but it's not an acceptable long-term solution:
Power on and boot test. Works fine, no magic smoke escaping from the hardware... touch screen works out of the box, so I can unplug the mouse (which means that the jammed-together USB stuff will no longer be an issue):
Next, install and fire up Guitarix. Plugged in guitar and headphones. Getting the software working well was quite a lot of work; the normal operating system setup does not work at all well for real-time audio processing and initially I was getting about 100ms latency with any non-trivial modelling going on. That's 1/10s between hitting the string and hearing the note, which makes it really hard to play at all -- I don't even want to imagine how hard it would be to keep in time with the rest of the band with that.
However, with some tweaks to the OS setup, that came down to 5ms, which is -- at least for me -- perfectly playable. If there is interest in this thread, then I'll post about that, because there's some interesting stuff in there about how digital audio processing works.
Anyway, what I've got here is a horrendous mess that actually works pretty well as a simple modelling headphone amp -- kind of like Amplitube, but no need to pay lots for branded models. I think the whole thing could be shrunk down quite nicely -- the limiting factors are the size of the screen, and the power supplies that will be needed (USB for the computing stuff, and probably 12v or so for the power amp stage).
Only problem so far is that there's a lot of hum when I'm not touching the strings or bridge on the guitar -- I suspect that there's an earthing problem, which sounds plausible with this hacked-together mess.
Reply With Quote