This page presents a simple simulation of the output and gain. There are 4 different signals shown for the selected overall signal level (tone, white noise, pink-noise, and speech shaped noise) - the spectra of these differ, and the levels shown are the levels in each 1/3-octave band. For each frequency band the hearing aid has a specified gain, kneepoint and compression ratio, with output limiting set at 95 dB SPL. The top-two graphs are the same apart from the linear vs logarithmic frequency scales. Some suggested exercises are given at the bottom of the page.
65 dB SPL
Suggested Exercises
The default signal levels are set to 65 dB SPL. Looking at the top-right plot how do the different signals differ across frequency. Which is highest at each frequency?
Again, looking at the top-right plot, how do the different signals noise signals change across frequency - which has the highest values at each of 250Hz, 1kHz and 8kHz?
Set the signal level to 30 dB SPL (well below the compression kneepoint), the signals and the output for the signals are different, but is the gain different for the different signals?
Set the signal level to 30 dB SPL (well below the compression kneepoint), now gradually increase the signal level, how does this affect the gain, which signal is affected first? Are the gains of all the signals affected equally across frequency? If no, why might that not be the case?
When the signal level raises enough, the level+gain reaches the 95 dB SPL output limit. What signal does this occur for first, and what frequency range? How does it change the shape of the gain plot for that signal? Think about why we should use a 90dB SPL tone sweep for measuring maximum output of a hearing aid.