EDIT: Sorry if this is the wrong sub-forum to post on. Feel free to move this over to the audio forum if it should rather be in there!

Hi guys!

My name is Adam! I'm new here! I'm currently in the early stages of building a multi-effects "pedal" (more like a desktop effects box (inspired by the Dreadbox Hypnosis)) that's going to be Teensy based. This is my first Teensy/Arduino project, so I'm a bit wet behind the ears, so I thought I'd shoot my shot on this wonderful forum and see if I could get a little help! Please note, this might be a long thread and there will definitely be some noobie questions in here!

So, this effects box is going to have a mono/stereo input and a stereo output. It'll feature 3 rotary encoders, an LCD screen and some other goodies which will be described further down in the post. Its usage is primarily thought to be for synths, EPs and guitars, both for home studios/jam sessions and live performance. It's going to have a fixed signal chain that goes as follows:

input -> amp -> chorus -> delay -> reverb -> LPF -> output

The input will just be line in on the Teensy 4.0 audio shield (rev D). I'm guessing I just go directly from my jacks and solder them onto the line input "pins" on the audio shield, right? Or do I need anything in the signal path in between the jacks and the audio shield? I know that most synths and EPs (and other similar TS/TRS output instruments) output standard line-level signals, but I'm not sure if it's the same for guitars? I think it is, but please correct me if I'm wrong!

I have an amp at the beginning of the chain, which is for gain staging, but perhaps the mixers in the audio system design tool are sufficient for that? Is the amp unnecessary?

Each of these effects will have 3 adjustable parameters (dry/wet being the third parameter for each), that will be controller with three rotary encoders (I might add a fourth if I feel like 3 adjustable parameters, one being D/W, isn't enough). These rotary encoders will additionally "represent" each of these three effects, so that by clicking on RE1, for example, will select the chorus and all three rotary coders will then control the adjustable parameters of the chorus. Clicking RE2 will select the delay and clicking RE3 will select the reverb. Long-pressing (I'm thinking 2s) each encoder will toggle a "bypass" (instant 100% dry) for each of the respective effects.

After the effects, the signal goes through a low-pass filter, that the user can toggle on and off with the flip of a switch. This filter is a little interesting, because the cutoff frequency for the LPF will be controlled via a ultrasonic distance sensor (I'm thinking about going with the HC-SR04), so that you can intuitively and interactively play with the cutoff frequency with hand movements above the sensor. This might look/sound super gimmicky and tacky to some people, but I think it's kinda cool. The idea is taking from the old Roland devices, like the SP-555, which featured the D-beam technology, which is essentially exactly what I described, only using an IR sensor instead. I might opt out of the HC-SR04 and go with an IR sensor instead, like the Sharp GP2Y0A41SK0F, since all the ultrasonic sensors I've found so far are extremely bulky and take a lot of space. The filter will be toggled with a switch, as previously mentioned. The on-state will engage the ultrasonic/IR sensor and allow for the cutoff frequency to be change, while the off-state will disable the sensor reads and set the cutoff frequency to a fixed 20k (or somewhere thereabouts).

Output is just going to be straight forward L+R line-level output, so I just have to solder the jacks to the outputs on the audio shield. Now, I do however have a question about the output pins on the audio shield. There's five pins: two marked L, two marked R and one ground pin between those. Are the two L pins identical (and subsequently the two R pins), or are these +/- pins for balanced L+R line level output signals? I can't seem to find any details on that.

Additionally to all of the above, I'll also have a little joystick (neat black joystick, like off of a Playstation controller) that I intend to incorporate into the device that'll work somewhat like an X/Y pad. I haven't decided exactly what stuff I'll be mapping to the joystick, but the Y-axis will be mapped to the dry/wet of all of the 3 effects, so that moving the joystick upwards will increase the dry/wet of all of the effects to 100% wet, while moving it all the way down will bring them all to 100% dry. The x-axis will work in a similar fashion, but with other parameters (but at least 1 parameter of each effect).

So far, I have gathered all of the parts, save for the sensor for the LPF and the switch to toggle the LPF on and off. I'll order that once I've decided between an ultrasonic sensor and an IR sensor.

Here is the "schematic" I have for the program, so far. It's early stages, so I haven't started writing the code yet. I think this schematic should work, but I'm new to this, so I might be wrong.
Click image for larger version. 

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I'd be immensely grateful if anyone could take the time out of their day to help me out with these questions I have! Also, if anyone has any comments/suggestions about this project, please let me know! As I said at the beginning of the post, this is my first Teensy/Arduino project. The development and execution of this product is my Major Project for my B.A.-degree in audio engineering, so I want to do this right and do it well!

TL;DR: I'm building an effects box with a couple of effects and stuff to control those effects and I need a little help!

Thank you so much in advance to anyone who's down to help me out with this project! I'm super excited for it and can't wait to get properly going with this.

Best regards,
Adam Murtomaa