Communication acoustics in Bell Labs

Abstract

Communication aoustics has been a central theme in Bell Labs research since its inception. Telecommunication serves human information exchange. And, humans favor spoken language as a principal mode. The atmospheric medium typically provides the link between articulation and hearing. Creation, control and detection of sound, and the human’s facility for generation and perception are basic ingredients of telecommunication. Electronics technology of the 1920s ushered in great advances in communication at a distance, a strong economical impetus being to overcome bandwidth limitations of wireline and cable. Early research established criteria for speech transmission with high quality and intelligibility. These insights supported exploration of means for efficient transmission—obtaining the greatest amount of speech information over a given bandwidth. Transoceanic communication was initiated by undersea cables for telegraphy. But these long cables exhibited very limited bandwidth (order of few hundred Hz). The challenge of sending voice across the oceans spawned perhaps the best known speech compression technique of history—the Vocoder, which parametrized the signal for transmission in about 300 Hz bandwidth, one-tenth that required for the typical waveform channel. Quality and intelligibility were grave issues (and they still are). At the same time parametric representation offered possibilities for encryption and privacy inside a traditional voice bandwidth. Confidential conversations between Roosevelt and Churchill during World War II were carried over high-frequency radio by an encrypted vocoder system known as Sigsaly. Major engineering advances in the late 1940s and early 1950s moved telecommunications into a new regime—digital technology. These key advances were at least three: (i) new understanding of time-discrete (sampled) representation of signals, (ii) digital computation (especially binary based), and (iii) evolving capabilities in microelectronics that ultimately provided circuits of enormous complexity with low cost and power. Digital transmission (as exemplified in pulse code modulation—PCM, and its many derivatives) became a telecommunication mainstay, along with switches to control and route information in digital form. Concomitantly, storage means for digital information advanced, providing another impetus for speech compression. More and more, humans saw the need to exchange speech information with machines, as well as with other humans. Human-machine speech communication came to full stride in the early 1990s, and now has expanded to multimodal domains that begin to support enhanced naturalness, using contemporaneous sight, sound and touch signaling. Packet transmission is supplanting circuit switching, and voice and video are commonly being carried by Internet protocol.