More than two octaves beyond the 3400 Hz limit !

During World War II researchers at the Psychoacoustic Lab at Harvard University determined that that the minimum bandwidth for adequate intelligible communication was 300 - 3400 Hz. More than a half century later the upper frequency limit of the phone remains 3400 Hz. Why? Do your customers prefer minimum bandwidth and just adequate intelligibility?

With the graying of the population and the increasing incidence of high frequency hearing loss in the younger population, the minimum bandwidth contributes to poor speech discrimination. Users confuse high frequency consonants as /s/, /z/ and /v/ because of their hearing loss and the limited frequency response of the phone.

The Virginia Solution

• Extract the time cues in the truncated phone signal
• Process these with proprietary algorithms
• Multiply the product by very high pitched carriers
• Combine the modulated speech with the phone signal
• Listen by air and bone to clear speech even in noise

		Figure 1 depicts the frequency spectrum of a sentence passed over a standard phone on the left and the same sentence simultaneously modulated by a high pitched carrier on the right. Both signals are fused into one perception by the brain. Figure 2. How do you get high frequency when the present filter phone band is used? The highest frequency time cues are extracted and multiplied by high frequencies. The high frequency speech sounds in the phone band are on the left and the same sounds are modulated on the right. The listener hears salient high frequency speech sounds missing from standard phone transmission. Figure 3 depicts natural speech with the full speech pass band along with the modulated speech. Modulation improves even natural speech in noise

			Lastly: 3 points to consider
			Loudness (volume) helps in a limited way because it adds some high frequencies due to cochlear nonlinearities, but it's outweighed by the distortion accompanying amplification. Bone conduction can deliver more high frequency cues than air conduction since it bypasses the low pass filtering of the middle ear. This is not the typical bone conduction telephone being marketed. It is a high audio frequency adjunct to standard air conduction telephones now in use. This technology is university developed, with one US Patent issued (4,982,434) and one in prosecution.
		For more information contact: Mr. Robert Guinta (800) 828-9687 Ext. 14

Page Content and Design : Dr Martin L. Lenhardt WebMaster: Alan G. Madsen Last update: Sunday, February 3, 2002