Question

a. what is digital code

b. explain why different types of codes are used to encode and decode data

c. discuss the reasons why hybrid codecs might be chosen over source codecs in voice over internet protocol communications

Answer 1

a. What is digital code

Digital coding is the process of using binary digits to represent letters, characters and other symbols in a digital format. There are several types of digital codes widely used today, but they use the same principle of combining binary numbers to represent a character.

b. Explain why different types of codes are used to encode and decode data

URL Encoding

URLs can only be sent over the Internet using the ASCII character-set and there are instances when URL contains special characters apart from ASCII characters, it needs to be encoded. URLs do not contain spaces and are replaced with a plus (+) sign or with %20.

ASCII Encoding

The Browser (client side) will encode the input according to the character-set used in the web-page and the default character-set in HTML5 is UTF-8.

In communications and information processing, code is a system of rules to convert information—such as a letter, word, sound, image, or gesture—into another form or representation, sometimes shortened or secret, for communication through a communication channel or storage in a storage medium. An early example is the invention of language, which enabled a person, through speech, to communicate what they saw, heard, felt, or thought to others. But speech limits the range of communication to the distance a voice can carry, and limits the audience to those present when the speech is uttered. The invention of writing, which converted spoken language into visual symbols, extended the range of communication across space and time.

The process of encoding converts information from a source into symbols for communication or storage. Decoding is the reverse process, converting code symbols back into a form that the recipient understands, such as English or/and Spanish.

C. Discuss the reasons why hybrid codecs might be chosen over source codecs in voice over internet protocol communications

Hybrid coding is an intermediate between waveform and source coding. Analysis-by-Synthesis (AbS) coding, which is performed in time domain, is the most famous type of hybrid coding. AbS codecs operate exactly as vocoders (source coding), but instead of using only two-state voiced-unvoiced model to determine the parameters of the linear prediction filter, the excitation signal is chosen by attempting to match the reconstructed speech waveform approximately the same as the original speech waveform. The speech signal is split into 20ms frames. For each frame, parameters are determined for a synthesis filter, and then the excitation to this filter is determined. This is done by finding the excitation signal which when passed into the given synthesis filter minimizes the error between the input speech and the reconstructed speech. Finally, for each frame, the encoder transmits information representing the synthesis filter parameters and the excitation to the decoder, and at the decoder the given excitation is passed through the synthesis filter to give the reconstructed speech. There are several types of AbS codecs. We can cite Multi-Pulse Excited (MPE), Regular-Pulse Excited (RPE), and the Code-Excited Linear Predictive (CELP) codecs. MPE and RPE codecs give good quality at rates of about 10 Kbps. CELP codecs can give the same quality at rates in the range 2.4 and 10 Kbps.