There do exist dedicated transcription services and solutions, for example VoiceBase or Translator Professional that can transform the speech from an audio (such as .aiff) and save the words in a textual format (.txt mostly) It may not always be perfect and commonly requires manual editing done by human.
Found 2 different conversion types using the same filename extensions.
Conversion aiff to txt type 1:
Convert from Audio Interchange File Format to Simple text.
On-line services software - convert aiff to txt on web
VoiceBase is a commercial platform for converting voice audio files to text, voice search and transcription.
File type (from-> to)
Convert from aiff file
Audio Interchange File Format
to txt file
The tables with software actions are a good pointer for what a certain program does with various file types and often may give users a good hint how to perform certain file conversion, for example the above-mentioned aiff to txt. However, it is not perfect and sometimes can show results which are not really usable because of how certain programs work with files and the possible conversion is thus actually not possible at all.
Conversion aiff to txt type 2:
Convert from Audio Interchange File Format to Steinberg LM-4 bank file.
Multiplatform software - convert aiff to txt on any platform
Translator Professional is a great software for instrument conversion. Going on 15 years and 80,000 licenses later, Translator is the gold standard when it comes to converting software AND hardware instruments to different formats.