Full Spectrum Hearing

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Benefits of Full Spectrum Hearing

The study of the acoustical energy in human speech and voice communication has historically been restricted to the frequency range below ~5 kHz because that is the range the typical conventional hearing aid is capable of transmitting. Evolving research has begun to evaluate the benefits of incorporating higher frequencies (>~5 kHz) with the results suggesting that a full spectrum of sound may deliver more natural sound and improved speech understanding in noise.

Figure 1

In 2003, Moore and Tan1 evaluated the perceived naturalness of music and speech based on the frequency bandwidth of the signal. Normal hearing subjects were exposed to speech and music stimuli that were band-limited at various high and low cut-off frequencies.

The data yielded these observations:

  • As the lower cutoff frequency widened, the perceived naturalness of sound quality increased. As the higher cutoff frequency increased, the perceived naturalness of sound quality increased.
  • The most natural sound quality is achieved when there is a robust representation of low and high frequencies.
  • Widening the frequency bandwidth resulted in an increase in the naturalness of speech score. The largest increase occurred when the bandwidth was increased to cover 123 Hz to 10.9 kHz (Figure 1).
  • Full bandwidth affects how natural speech sounds to a listener.

Figure 2

Recent data by Levy and colleagues2 highlights another potential benefit of high frequencies: improved speech understanding in certain complex listening situations. This study evaluated the benefit of extending the audible frequency bandwidth out to 10 kHz for both normal and hearing impaired subjects.

 

Using the Hearing in Speech Test in both an asymmetric and diffuse-noise set-up (Figure 2), Levy et al. found that extending the bandwidth from 4 kHz to 10 kHz significantly improved the participants’ speech reception in the presence of competing talkers.

 

These results demonstrate that the addition of high-frequency information above 4 kHz can improve speech understanding in certain situations with spatially separated sound sources, a characteristic of many difficult listening situations. This shows a potential benefit of broadening the frequency range of amplification delivered to patients with hearing impairment.

1. Moore, B. C. J., & Tan, C. T. (2003). Perceived naturalness of spectrally distorted speech and music. J Acoust Soc Am, 114, 408–419.

 

2. Levy, S.C.; Freed, D.J.; Nilsson, M.; Moore, B.C.; Puria, S. (2015). Extended high-frequency bandwidth improves speech reception in the presence of spatially separated masking speech. Ear Hear, 36, e214–e224.