How to get voice in raw format by using mic in linux

Here are some useful links that will teach you how to capture voice data using ALSA -

1. Resource 1
2. Linux Journal

Here is a link that will give you some insights about ALSA and its configuration.

This is the official ALSA API Reference.

This may be out of context but here is a list of recommendations that you should keep in mind while doing audio programming.

If you would like some alternatives to ALSA then I would suggest to take a look at Port Audio.