The file type is to some extent only relevant in terms the degree of support for the format used, ie how universal the format is required to be for playback on different devices.
The major determinants of file size are, in decreasing order of effect, Bitrate, Samplerate and to a small extent bit depth.
My recommendation would be use the audio file type that meets point 1, then carry out a series of tests adjusting (lowering) the Samplerate first to get it down to a usable level, then adjust (lower) the Bitrate, to the lowest level that the audio still remains usable.
This is a balancing act between Bitrate and Samplerate to maintain a usable audio file, getting 'one size fits all' balance btween the 2 parameters may/may-not difficult depending on the audio content.
HI John, I will play with different Bitrates to see if I can reduce the size of the files to be emailed. Simple audio files that don't require audio quality...voice message, phone conversation content, MP3 is good enough for my purpose.Mono is also an option. Thank you for your quick response.
Yes, a single-channel mono MP3 will have about twice the resolution of a stereo MP3 encoded at the same bitrate with roughly the same file size. For instance, a 64kps mono MP3 file will have the resolution of 128kps at the 64kps file size.Which is great for the above mentioned content and/or where spacial content is not needed.
FWIW, in my 'sum and difference' experiments, a spoken word 320kps mono MP3 and the PCM mono master file cancel out in excess of -60dBFS when the polarity is reversed on one.