Low bit rate coding of high quality digital audio: algorithms and evaluation of quality

Based on frequency domain techniques, coding of high quality digital audio with bit rates of down to 64 kbit/s is possible.The NMR (Noise-to-Mask Ratio) has been introduced for quality evaluation and optimization for low bit rate coding schemes. Real time implementations of low bit rate codecs and a measurement system have been developed. Several coding schemes (Optimal Coding in the Frequency domain (OCF), Low-Complexity Adaptive Transform Coding (LC-ATC), Sub-Band Coding (SBC)) are compared using NMR. Comparison results for different types of music and testsignals are presented.