Logarithmic non-uniform quantisation that delivers a constant signal-to-quantisation noise ratio (SQNR) across all input signal levels. The benefit and price of non-uniform quantisation are also quantified in terms of companding gain and companding penalty.A comprehensive treatment of A-law and m-law PCM source coding standards, including derivation of the standards from the ideal logarithmic compression curve through piece-wise linear approximations, detailed SQNR analysis, and performance comparisons with linear ADC. Lossy data compression: A brief overview highlighting various categories of low bit rate speech coding, namely waveform coders, vocoders and hybrid coders. The discussion particularly focuses on speech quality measures and trade-offs in low bit rate speech coding, and on differential quantisation, linear prediction and various special cases of bit rate reduction, including ADPCM, ADM and LPC-10.