can not set sampling rate and encoding bit rate for MediaRecorder

I need to record the user voice in good quality many times. I can not use AudioRecord-AudioTrack approach, because I got huge size files and it is not appropriate for me. 3gp format + nb encoder give me poor quality of recording. So I decided to use mpeg4 format with aac encoder, but their default bit rate is 8.000kHz and I want to raise开发者_开发问答 this value. I tried to use methods setAudioSamplingRate and setAudioEncodingBitrate, but they did not affect on record quality. I put different values for these method (16, 20, 16000, 40000, 44100, 96000) without any result. Maybe this is device specific behavior - I use Samsung Galaxy Tab. Does somebody know how to make the audio recording quality better?

Many devices only provide mono recording.