Version for all android phones: https://play.google.com/store/apps/details?id=multimediasol.app.microphone
This version works best for android O and below supported Samsung phone only. From android P this app will work like the version for all android phones

This application will connect the microphone of your phone to headphone or external speaker. It allowed to speak in realtime with low latency no delay or lag like a professional microphone. You will hear your amazing voice instantly.
Version 2.0 added recording feature with high quality audio .
This version doesn't support wireless connection (bluetooth...) because of technical reason. Download the version at the link below to try bluetooth
https://play.google.com/store/apps/details?id=multimediasol.app.microphone

User has to connect the phone to wired headphone or external speaker for this application to work. Because the speaker of the phone doesn't have big volume.
Below are some common usecase.
- Sing karaoke with music in your phone.
- Giving speech in front of people (for example inside an office) like a professional microphone.

Version for android phones with mid-range hardware: https://play.google.com/store/apps/details?id=multimediasol.app.microphoneall