Question
I am new to dispensing wireless transmission systems. What is the difference between analog versus digital sound transmission?
Answer
For good speech perception, the sound should be transmitted with as little interference as possible. In other words, there should be no radio interference, and the sound transmission should be stable. The user should experience a constant sound, without interruptions or delays. The disadvantages of analog transmitting techniques include audible transmission noise and low dynamic range, caused by frequency and amplitude signal compression. The dynamic range of a system should match the dynamic range of the signal to be transmitted. Where speech is to be transmitted, the dynamic should range from 20 - 30 dB to 75 - 80 dB to cater for amplitude levels. The frequency bandwidth should be about 250-7000 Hz. If there is a low dynamic range in the transmission chain, loud speech may be distorted, quiet voices may be masked by background noise and drop-outs can occur. In these instances intelligibility can be negatively affected.
The input/output curve in Figure 1 shows the wider dynamic range of digital transmission of sound known as Secure Stream Technology (SST) in the Comfort Digisystem from Comfort Audio, as compared to a typical FM system. When there is insufficient dynamic range in any part of the transmission chain, the loud parts of speech may be distorted while the weaker sounds of speech may be masked by background noise, and speech understanding will be impacted.
Input-output curve of digital transmission Secure Stream Technology (SST) of Comfort Audio (red) with that of a typical analog FM system (blue).
SST transmits speech to a hearing aid listener, without transmission noise and with minimal distortion. SST technology provides crystal clear, eavesdrop-secure sound transmission, in less than half a millisecond, and with low energy consumption.
Thank you for your question. More information about the Comfort Digisystem with SST can be found at: www.comfortaudio.com/us/ or on the Comfort Audio web channel on AudiologyOnline.
August Pansell is a development engineer with a degree from Halmstad University, Sweden. He is one of the owners and founders of Comfort Audio. He started the company together with Carljohan Lagervall in 1994. In 2011, Comfort Audio was awarded with the "Best New Product Award" at AudiologyNow! and the "Swedish Embedded Award".