TruSound Stabilisers

The compressors will always attempt to apply the optimal gain in every situation based on the design criteria of audibility, intelligibility, preservation of contrast and comfort.

Because there is evidence (ref. 1 and 2) to suggest that hearing aid users prefer the sound quality generated by a slow acting compression system, the default compression mode in a Widex hearing aid is slow-acting. But there will be situations where slow-acting compressors will not suffice. This is where the TruSound stabilisers help.

The TruSound stabilisers help preserve the high sound quality expected from the TruSound compression system in demanding situations also.

The TruSound stabilisers are designed to handle special situations with quick changes in the environment and to prevent smearing of the temporal and spectral contrast in the signals.

Quick changes in loudness level

Loud sounds should not have the same amount of gain as is applied in a quiet environment. Therefore, when the sound level increases rapidly, the hearing aid must be able to react very quickly.

The TruSound stabilisers are a fast-acting mechanism that is able to lower the gain quickly to adapt to the louder sound level.


The figure (click for large picture) shows a sound signal played by the hearing aid with and without the activation of the TruSound stabilisers.

Without the TruSound stabilisers, full gain is applied to the loud peaks, which will sound very loud to the user. When the TruSound stabilisers are activated, on the other hand, the peaks are dampened.

Another situation where the TruSound stabilisers would be activated is when the hearing aid user receives a mobile call during a loud party and leaves the room to answer.

The TruSound stabilisers make sure that gain is changed quickly from the low gain needed in the very loud party environment to the gain needed for normal conversations.


The top panel shows the amplified signal in the party situation without the TruSound stabilisers being activated. The bottom panel shows the amplified signal in the mobile phone situation with the TruSound stabilisers activated.

It can be seen that the soft part is quickly amplified when the TruSound stabilisers are activated.



References:

1. Hansen, M. (2002). Effects of multi-channel compression time constants on subjectively perceived sound quality and speech. Ear and Hearing, 23(4), 369-380.

2. Neuman, A.C., Bakke, M.H., Mackersie, C., Hellman, S., and Levitt, H. (1998). The effect of compression ratio and release time on the categorical rating of sound quality. Journal of the Acoustical Society of America, 103, 2273-81.