Task 1:
Speech is the ability humans have developed to communicate between themselves with the sound produced by their mouth and nose.
There are two types of speech sounds: The voiced and unvoiced one. A voiced sound is created when air pass through our vocal cord in direction of the mouth. This air vibrates in a certain frequency, normally between 50 and 400 Hz that produces the sound heard and desirably understood by the receiver ears. This frequency is controlled by varying the shape of the air channel, as changing the mouth position or the tongue, working as a filter, allowing the desired frequencies for the expected sound to pass; and by the speaker age and sex.
The unvoiced speech are created by making air go through an opening, not vibrating the vocal cords, and, consequently, not been as …show more content…
This process is done by sampling, quantization and encoding. These waveform coders do not have any previous knowledge about the signal being converted, meaning that, theoretically, they should be signal independent.
Generally, these coders work at sample rates above 16 kb/s, degrading the recovered speech quality drastically if it works below this rate.
They usually are Time Domain or Frequency Domain coders. The simplest coder is Pulse Code Modulation (PCM), which is a Time Domain coder. Its task simply involves sampling and quantizing the input signal. Its main problems are the requirement of a high bit rate around 96 kb/s and the high susceptibility to channel errors. Other types of Time Domain coders are the Differential Pulse Code Modulation (DPCM) and the Adaptive Differential Pulse Code Modulation (ADPCM), which uses the predictability of the signal to predict it, and quantize the difference between the predicted and the original signal making the bit rate to be transmitted smaller for the same