You should be more specific: what kind of analysis are you interested in? For what language?
If you want to perform basic NLP tasks on English texts I suggest you the Stanford CoreNLP suite, which offers tools for POS tagging, parsing, NER and sentiment analysis.
Thank you Alex Mircoli for your kind reply. I am looking for a tool that could perform a NLP, historical analysis of keywords, and Sentiment analysis.
The object of my planned study are policy documents and Parliamentary archives. I am an amateur in Digital Humanities scouting for potential software tools.
I believe CoreNLP would solve most of my problems.
You should try out the Google text-to-speech/speech-to-text and see how you get on, that will at least help with one part of the problem: https://cloud.google.com/speech-to-text/
You could then do some statistical analysis of the text in something like Nvivo.