1. A microprocessor controlled speech synthesizer for generating the audio information of a set of characters which includes a first subset of lower case letters and a second subset of upper case capital letters so that the operator can audibly distinguish between upper and lower case letters from an external input, said synthesizer comprising; a microprocessor unit connected to a first memory for the storage of speech data and to a second memory for the storage of externally originated input characters, said microprocessor unit comprising control means responsive to said speech data from the first memory for forming a speech pattern corresponding to said input characters; a speech generator connected to said first memory and controlled by the control means of said microprocessor for producing audio signals representing said set of characters; said microprocessor unit further comprising a character recognition means connected to said first and second memories and to said speech generator for recognizing from the externally originated input characters those characters which belong to said second subset of upper case capital letters and for introducing a first modification in the speech pattern for said characters belonging to the second subset; said first modification comprising a changing of at least one pitch component or a changing of a voice characterizing component of the speech pattern while maintaining the identity of the second subset of upper case capital letters; said microprocessor further comprising a position determining means for determing the position of at least one letter of a word made up of characters presented and for introducing a second modification in the speech pattern for said letter while maintaining its identity, said second modification comprising a modification of a pitch component and/or a voice characterizing component of the speech pattern.
8. A device as claimed in claim 1, characterized in that said second modification of a pitch component of the speech pattern comprises a lower pitch with respect to a mean pitch component of the speech pattern.