A little education for those who want to know how to refer to compression.
Knee point: Knee point refers to the point where compression kicks in. Sound above the knee is being reduced by a specific ratio, so the climb to peak output is no longer going straight up, therefore it looks like a bent leg, because the output is being reduced by a specific ratio, hence “Knee Point.” A knee point that is too low means that in a noisy restaurant, or driving down the road at interstate speeds, the aid is always in compression. This is why we hear complaints of:" I can hear everything in the restaurant except the people at my table." Compression is “Compressing” the smaller sounds of speech out of the output signal.
Compression Ratio: The ratios can range from 1.1:1 to 3.0:1. What this means is that at say 2.5:1 compression ratio, above the knee point, it takes 2.5 db into the hearing aid to get on into your ear. Too high a compression ratio does a number of things, most are negative to the user’s experience. It distorts the signal, it makes everything sound sort of “Donald Ducky.” It compresses out the smaller sounds of speech needed for clear understanding, and it induces a much higher “Noise Floor” (the amount of noise present in the aid in perfect quiet)
Attack time: Attack time is measured in milliseconds, and refers to the time it takes the hearing aid to begin to reduce sounds above the knee point by the pre-determined ratio, in other words when compression kicks in.
Release Time: Release time is the amount of time, also measured in milliseconds, that it takes the aid to back out of the compression state after the offending noise is no longer present in the environment. Attack and release times that are too fast give the user a feeling of “pumping” as the noise level of an environment rises and falls, or transient noises occur, like slamming doors, or someone laughing loudly.