To record sound from volca keys and tinypiano

I want to record the sound sample and use in my piano app. 

211214 best is usb sound adapter with otg. Then use caustic editor to reduce noise and amplify it. 

The below method does not work. I find that the usb sound adapter does work. But the sound is do soft. 

Direct to mac, there is back ground noise. Direct to android via otg is louder but still soft. Iphone does work with usb camera connector but is still soft. 

1. 3.5 mm stereo out cable from korg tinypiano and volca keys. 

2. 3.5 mm mono to mac usb. 

3. Stereo cable does not work on the adapter. Need to convert to mono. 

1. I need a stereo to mono converter plug. The stereo cable cannot connect to microphone input. Does not work.

2. I need a 3.5mm splitter for audio out and mic in. It actually works on iphone. The trick is only feeling the connection. I have push too much into the adapter that it breaks.  Does not work. 

3. It is also possible to record on PC.