(a 5 minute search and this will come up:)
Microsoft Agent uses by default the Lernout & Hauspie TruVoice Text-to-Speech Engines to produce speech. This engine comes in many languages (to be downloaded) and each language has his own voice. But for English there are 3 different voices:
Sam - Male Voice (English) 2.1MB (default one included in Windows)
Mike - Male Voice (English) 2.4MB
Mary - Female Voice (English) 2.3MB
There are also other TTS Engines from many other speech vendors, including versions of ATT Natural Voices, Digalo, Elan Speech, IBM ViaVoice, etc... The only requirement is that the TTS Engine is SAPI 4.0 compatible. SAPI 5.0 is not currently supported.
http://www.microsoft.com/msagent
http://www.microsoft.com/msagent/downloads
PS: of course, each voices can individualy be tweaked. You can alter the speed, tone, color, etc., so maybe you don't need another voice at all, but just tweak it a little bit (tool for this can also be downloaded. Search the MSAgent Homepage or Google it). A bad tweaked voice can sound very bad...
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