A computer system used for speech synthesis is called a speech computer or speech synthesizer, and can be implemented in software or hardware products. A text-to-speech (TTS) system converts normal language text into speech, the quality of a speech synthesizer is judged by its similarity to the human voice and by its ability to be understood clearly. Panopreter Basic is a text-to-speech and text-to-mp3 freeware program, it reads text files, rtf files, web pages and word documents with natural voices, it also converts these files into wave and mp3 files, so users can import the generated audio files to portable devices such as iPod and mp3 player, and listen to them while walking, jogging or commuting to work. A speech synthesis tool can be used as language learning tool, students can improve pronunciation and listening skills with it in language study. Microsoft provide their text to speech voices on Windows operating systems. On Windows 8 or 8.1, there are three text to speech voices available: Microsoft David (US male), Zira (US female) and Hazel (UK female). On Windows 7 and Vista, the text to speech voice is Microsoft Anna (US female). On Windows XP, Microsoft Sam (US male) is the only text to speech voices. These are standard American or UK English, Microsoft provide a wide variety voices in other languages too, such as French, German, Spanish etc..