Bandwidth extension of speech signals: a catalyst for the introduction of wideband speech coding?

The restricted audio quality of today´s telephone networks is mainly due to the narrowband (NB) limitation to the frequency range from about 300 Hz to 3.4 kHz. Meanwhile, codecs for wideband (WB) telephony (50 Hz to 7 kHz) exist with significantly improved speech intelligibility and naturalness. However, the broad introduction of wideband speech coding requires strong efforts of both network operators and their customers because many elements of the networks (i.e., terminals and network nodes) have to be modified. An intermediate step to overcome the narrowband limitation can be achieved by applying artificial bandwidth extension (BWE) in the receiver. In this article we review the basic principles of bandwidth extension, and discuss several application scenarios in which both wideband coding and BWE complement each other. The introduction of BWE methods in terminals and networks may help to speed up the introduction of true wideband speech coding in the near future