http://*.com/questions/6284651/avaudiorecorder-doesnt-write-out-proper-wav-file-header
http://*.com/questions/32312508/audio-file-format-issue-in-objective-c
https://developer.ibm.com/answers/questions/180732/seems-watson-text-to-speech-service-returns-a-wav.html
bit conversion相关：
http://*.com/questions/7332641/converting-nsdata-to-int
http://*.com/questions/8552864/bit-conversion-tool-in-objective-c