What are various AMR Encoder modes?

MR122 : 12.2Kb/s

MR102 : 10.2Kb/s

MR795 : 7.95Kb/s

MR74  : 7.4Kb/s 

MR67  : 6.7Kb/s 

MR59  : 5.9Kb/s 

MR515 : 5.15Kb/s 

MR475 : 4.75Kb/s 

references:

https://books.google.co.in/books?id=767W1gWhj_oC&pg=PT363&lpg=PT363&dq=what+is+mr122+in+amr+encoder&source=bl&ots=sZEUJbMCW9&sig=_xVA4FxKQuEakBsTes_ZnxnIx0A&hl=en&sa=X&ved=0ahUKEwiK2IiG9qDTAhUFqo8KHRh8AFEQ6AEILjAC#v=onepage&q=what%20is%20mr122%20in%20amr%20encoder&f=false