I have always used maps that give IQR, ALG, Cspeech, ASR, TTS, & HNR. ie - 5412 in the latest release of maps.
I choose this version because I prefer to listen to Serena advanced human voice for instructions that has road numbers and street names.
I will visit the USA shortly and the only USA map available at the moment is 5447 which only has IQR, ALG, TTS, & HNR. No Cspeech!
I assumed that TTS gave a digitized voice and Cspeech gave a human voice to the same information?
Can anybody clarify - what is the difference between Cspeech and TTS?