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Check this site out http://www.data-compression.com/index.shtml
its has every thing about speech processing its mathematical model lossy & lossless compression techniques explained and even source code of the algorithms are made available.
In this post i will define what exactly pitch is and remaining things later.
The speech signals of human beings are produced because of the excitation of the vocal tract with the exciation signal coming out of the vocal cords. The speech is mailny categorized in to voiced speech and unvoiced speech. The voiced speech is because of the periodic exciataion of the vocal tract. If we can model the VT as filter, the excitation signal(the input to the filter) is a periodic signal. The fudamental frequncy of this periodic signal is called pitch. As this signal is generated from vocal cords the pitch is dependent on the size of the vocal chords. For males the size is big when compared to that of the females and children. The one period of opening and closing of the vocal chord is called pitch period which is reciprocal of the pitch. Note that pitch and pitch frequency means the same.
For unvoiced case the excitation singal is noise like signal.