How to improve the quality of AMR audio recordings in Windows?

What are you recording? I guess you are talking about the material you were referring to in your previous questions. If so, then you can't really improve the quality.

To be more general: You can't improve the objective quality of a recording after it is done.

You could improve:

• The microphone used for recording
• The signal chain altogether (cables, shielding)
• The analogue to digital converters
• The file format (i.e. using uncompressed WAV instead of AMR or MP3 files)

If you have a small voice recorder, as I would guess from your questions, you obviously can't change anything of this except for using a directional external microphone which would help make voices stand out from ambient noise.

A super-cardioid microphone is similar to a hyper-cardioid, except there is more front pickup and less rear pickup. These three patterns are commonly used as vocal or speech microphones, since they are good at rejecting sounds from other directions.

In my previous answers however I mentioned equalizing as a proper technique to filter noise out and improve voice recognition. This might help you subjectively improve the quality.