AIC3254 - stereo DRC and stereo limiter blocks.

Hi,

I was wondering if anybody has made use of the stereo DRC and limiter blocks available in the AIC3254 ?

How well do they work ? Does the stereo limiter implement an equivalent of an adjustable diode-clipper ?

Essentially here is the info on the "Fast Stereo Limiter" block :

Out_L1 = In_L1,                                                if |In_L1| < Limit

           = Limit + Ratio*(InL1 – Limit)               if InL1     > Limit

           = -Limit + Ratio*(InL1 + Limit)              if InL1     < -Limit

Out_L2 = In_L2,                                                if |In_L2| < Limit

           = Limit + Ratio*(InL2 – Limit)               if InL2     > Limit

           = -Limit + Ratio*(InL2 + Limit)              if InL2     < -Limit

This component is useful in speaker protection use cases. Signals containing sudden high amplitude peaks might often escape the DRC. This component is useful in limiting such signals if placed after the DRC.

As it is suggested here I'd like to use it in conjuction and following a stereo DRC block. However, for speaker protection and most of all, for use in hearing protection and hearing safety applications, the note above is worrying ''Signals containing sudden high amplitude peaks might often escape''. This is not encourraging  to hear as I am considering this codec for industrial environment where hearing protection is paramount and where unexpected noises exceeding 85dB(SPL) are not uncommon. I have some other ideas in mind, but being fairly familiar already with the AIC3254 for some other applications, I thought it could be a go ... Am I possibly expecting too much from this little chip for such uses.

For instance,I know the AGC attack time is adjustable to a minimum that is not zero, and this tells me already that fast/loud audio impulses will possibly be too fast and of high volumen to permit de AGC to settle within reasonable limits. If the AGC gain is reduced from say, maximum, donw to zero, beyond this level there is no further compression adjustment possible and the input signal will continue to increase, potentially to unsafe limits.  So this is where the fast limiter comes in. Will it act as a hard-limiter if configured as a such, so that such fast & loud impulses that get trough a DRC will eventually be tamed by the limiter to an absolute maximum possible level ? I have not tried it but has anybody listened to the generated distortion ? Is it obvious and unpleseant as for hard clipping, or is there more to the implementation than I think ?

Regards, Mike