Bridging the gap. Extending MPEG audio down to 8 kbit/s

MPEG Audio is more and more becoming the "do-it-all"system for applications in speech and audio coding ranging from a few kbit/s to several hundred kbit/s. Originally devised for transparent coding of high quality audio the market place demands the application of the same ideas to "intermediate quality" audio or even speech coding at bit rates comparable to those of classical speech coding schemes. The paper gives an overview over recent developments regarding audio coding at bit rates below 64 kbit/s/ch. These include the MPEG-2 Low Sampling Frequencies mode, MPEG-2 Advanced Audio Coding (MPEG-2 AAC) and MPEG-4 audio.