Description
ITU-T companding standard used in the conversion between analog and digital signals in PCM systems. A-law is used primarily in European telephone networks and is similar to the North American mu-law standard.
Complete Definition
An A-law algorithm is a regular companding algorithm. For optimizing or modifying the dynamic range of an analog signal for digitizing, it is utilized in European digital communications systems. It is fairly akin to the mu-law algorithm used in Japan and North America. The wide-ranging active range of speech does not lend itself well to proficient linear digital encoding.
A-law algorithm encoding efficiently lessens the dynamic range of the signal. Thus, the coding effectiveness gets increased and results in a signal-to-distortion ratio which is advanced to that obtained by linear encoding for a particular number of bits. A-law algorithm is an audio compression scheme defined by Consultative Committee for International Telephony and Telegraphy or CCITT G.711 which constrict 16-bit linear PCM data down to 8 bits of logarithmic data. By restricting the linear sample values to 12 magnitude bits, the A-law compression is defined by its equation. In the equation, A is the compression parameter and x is the normalized integer to be compressed. It is a linear estimation of logarithmic input/output relationship. It is put into practice by using 8-bit code words. 8-bit code words permit for a bit rate of 64 kilobits per second.
By multiplying the sampling rate by the size of the code word, this is calculated.A-law algorithm breaks a vibrant range into a total of 16 segments. There are 8 positive and 8 negative segments. Each segment is twice the length of the preceding one. Within each segment, homogeneous quantization is used. For coding the 8-bit word, 1st (MSB) identifies polarity. Then, bits 2, 3 and 4 recognize segment. The final 4 bits quantize the segment.A-law algorithm has certain edges over the mu-law algorithm. The A-law algorithm provides a somewhat superior dynamic range than the mu-law algorithm, at the cost of substandard relative alteration for small signals. For an unvarying PCM, A-law algorithm calls for 13-bits. For using A-law algorithm, a worldwide link is mandatory.The application of A-law algorithm has been observed extensively
Both a-law and u-law are companders for the G.711 voice codec
A-law Compander formula (from Cisco's Waveform Coding Techniques )
Also useful is the : ITU website and search on a-law