If there is no sound in your call/surround voice recordings, then you need to set the voice recorder to "Stereo" mode on Samsung phones.
Samsung Galaxy S flagship devices support audio recording in stereo mode that makes your recording sound much better. On some devices it is called Interview mode. Of course it works only on models equipped with two microphones. Here is how to switch voice recorder app to stereo mode on Samsung Galaxy devices.
1. Open Samsung Voice Recorder - Settings:
2. Scroll to Advanced section and tap on Channel setting:
3. Select Stereo:
Now you can record audio in stereo mode and the call/surround recording will work.