I am looking to mix music from a smartphone (e.g. Pandora) PLUS voice from a microphone (e.g. person singing) and output the two “tracks” to headphones for somebody to listen to. Please see my simple hand sketch to get a bettery visual.
I am not interested in recording. I just want real-time mixing of the music + mic and output this to headphones.
This is almost like a Karaoke machine. But rather than broadcasting the music + voice to loud speakers, the output is ported to headphones.
They both have a single stereo input, I don’t think they will be able to do what you’re looking for. Even if you’re able to stack two shields, you still need to write the software that makes everything work and somehow connect it to your phone. I think it would be possible to do, but it might get expensive and time consuming to write the software that makes everything work. You might try asking on [PJRC’s forum, it’s possible someone there might have more advice for how to make this work.](https://forum.pjrc.com/)