Digital Radio Avoids Falling Off a Cliff

One of the classic problems with digital technology is what is known as the "cliff effect": when digital signals reach their limits, they don't fail gracefully like analog ones do---they go off a cliff and crash hard. Not only has the tendency for digital signals to exhibit their limitations noisily in the audio recording and playback environment been a problem for engineers and listeners, the effect on the digital broadcast industry has been tough to circumvent as well---until now.

Last week, Lucent Digital Radio, a wholly owned venture of Lucent Technologies, announced a technical advance in its In-Band On-Channel (IBOC) Digital Audio Broadcast (DAB) system that they claim solves the problem of providing high-quality digital audio reception over a coverage area equal to that of current analog FM stations. Lucent Digital Radio also announced that it will offer digital radio broadcasters royalty-free licenses for its IBOC DAB system, which will be field-tested this year.

Lucent Digital Radio's advancement, called Multi-Streaming, is based on what the company describes as "state-of-the-art capabilities in audio and wireless channel coding technologies" from Lucent's Bell Labs, and allows for the "best-quality" FM audio to be delivered over a wide coverage area, even under impaired channel conditions. "This new advancement with Multi-Streaming now makes possible a fully digital solution to IBOC even in the hybrid mode, eliminating the need for receivers to fall back on the analog signal," said Suren Pai, president of Lucent Digital Radio.

Multi-Streaming, developed recently by Lucent Digital Radio's technical team, is intended to allow new IBOC receivers to transparently reconstruct the digital signal to deliver the best-quality sound possible anywhere in the service area for a broadcast. So far, digital broadcast systems designed to operate during a multi-year transition period from analog to digital could be received in just a portion of the analog service area. With Lucent's new approach, the digital signal will be receivable throughout the current analog service area.

Lucent claims that with Multi-Streaming, the digital signal emulates the graceful degradation characteristics of analog signals, instead of the annoying "cliff effects" or "digital drop-outs" experienced by earlier digital systems. Lucent says this allows for high-quality digital audio even at the edge of analog coverage. The company further states that the Multi-Streaming approach works with both AM and FM IBOC systems and is integrated with Lucent's Perceptual Audio Coder. The PAC encoder converts analog audio signals into a digital signal, then compresses the data by a ratio of at least 15:1 at bit rates lower than 96 kilobits per second (Kbps).