Back from a family holiday, I'm really looking forward to testing out some ideas on this project.

One thing I require is to either have polyphonic output to allow the pads to trigger simultaneous sounds, or at the very least simulate it to the human ear.

I've written several test code scripts for the Arduino board and shield I had in mind for this, but find that I can't really get close to the effect I had in mind. More likely to be my execution rather than the board itself.

Before I went on holiday I threw together a quick novelty project at work; an ESP8266-based webserver to allow triggering of soundclips in the office (all for the proverbial shits and giggles :-D ). This project used the DFRobot mp3 board, and it was a doddle; controlled via software serial and complete with an arduino library, the thing worked great. Also, it was really cheap!

I'm going to order a few of these boards to test an idea - if it works, great, if not I'm sure the boards will work their way into other projects ha ha!

The plan is to add two or more of these mp3 players into the project, with an arduino or ESP8266 reading the pads and connected to the players, and a DIY mixer to blend the outputs of the players.

Two strategies - one would be to check whether the first board is busy playing a sound file and send the request to the next available board. The other would be just having a player per pad. There's only 4 pads so 4 players would be doable.

If the multiple players work together then this will be great for the project. The only drawback would be the need for multiple SD cards but, once the sounds are added to them this shouldn't pose an issue.