From time to time I have some files which I need to transcode for my personal mp3 player to play it.
They may be recordings in other formats or even videos.
I like to use VBR, as it gets the best quality/size ratio, but much of the times I really don't really know the input audio quality, so I don't know what quality to use - I don't want to use VBR0 for a poor quality input (and waste space) nor do I want to use a low output quality for good recordings.
So, the question is: how can I know what VBR quality would best fit the source file's quality?
Is there a way to know what is the highest MP3 bitrate that a file would need to [almost] not loose quality?
I've heard about things like frequencies analysing, but really don't know what they are nor how to do them, so if that's the way, I appreciate any further info.