Electronic Design

Streaming Audio Connects With Tiny Hearing Aids

When I go to the movies with my wife, hearing and understanding the film’s dialogue is never a problem for me or for her. But when we watch a movie at home, the volume that I think is suitable is always too loud for her.

This led me to start wearing wireless headphones so we’re both comfortable with the sound while watching the movie. These headphones are big clunky things, though relatively comfortable. But it makes me wonder if I’m experiencing hearing loss or if my wife has exceptionally acute hearing.

Streaming for Comprehension

For those whose hearing loss demands the use of a hearing aid, watching TV can be tricky. Many hearing-impaired people report that they struggle to understand speech on TV, even after receiving new hearing aids. Part of the reason is that hearing-impaired individuals generally need a more positive signal-to-noise ratio (SNR) to have the same speech recognition as people with normal hearing.

Back in 2010, Pickart Hearing Service published an article that described an investigation of how well viewers understand speech on television using a hearing aid alone versus using a hearing aid and an Oticon TV adapter and Streamer. In this case, the hearing aids were Oticon Epoq devices.

Testing was conducted with unmodulated noise playing from two speakers at 45° and 315° from the subject. The noise was speech-spectrum-shaped unmodulated noise filtered to match the long-term spectrum of the television test material.

The noise level used depended on the individual’s speech reception threshold. The better the participants’ speech reception threshold, the louder the masking noise. The range of SNRs tested was 0 to +12 dB. The level of the masking noise was varied individually to avoid problems with floor and ceiling effects, which can be a problem for tests with a fixed SNR.

The test’s results showed significantly greater speech recognition with the TV adapter system over hearing aids alone. The range of improvement was between 15% and 66% with an average of 45% improvement.

The authors concluded that the key to improving speech understanding is improving the SNR. The TV adapter system improves the SNR for the television by providing a louder clearer signal that isn’t affected by the room noise. The signal isn’t affected by room noise because the digital signal is sent from the TV adapter to the Streamer, which then sends the signal to the hearing aids.

Add Smart phones to the Mix

GN ReSound has developed a hearing aid called the ReSound Alera. It employs Nordic Semiconductor’s nRF24L01+ chip, which uses Nordic’s proprietary 2.4-GHz wireless technology. The idea here is to wirelessly stream audio not only from TVs, but also from smart phones, PCs, laptops, tablets, and other devices via an audio streamer adapter or Bluetooth connection.

The entire ReSound Alera series is built around a miniature (2.0 by 1.5 by 0.6 cm) product form factor that has to embed an even smaller electronic module (1.4 by 0.6 by 0.4 cm) housing an antenna without groundplane (due to lack of space), Blue-tooth radio, the Nordic nRF24L01+ radio, plus an external microcontroller to perform the advanced audio signal processing—background noise cancellation and surroundsound processing—required in a hearing aid (see the figure).

“It was extremely challenging to achieve this ease of end-user functionality, along with medical-grade field reliability and real-time audio performance in a hearing aid as small as an adult fingernail weighing as much as a paper clip,” said Thomas Olsgaard, vice president of hardware platforms at GN ReSound.

Noting the power challenge, too, Olsgaard explained, “All of this functionality needs to run for several days from a replaceable ZincAir battery—a fuel coin cell that stores around three times more energy than a standard coin cell. This meant that the proprietary radio needed the lowest possible power consumption to enable the product to average 1.5 mA in operation and peak at 4 mA when streaming.”

As for me, I’ll be sticking with my clunky wireless headphones for now. But it’s good to know that these new hearing aids and others like them can provide such state-of-the-art capabilities.

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