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Low level signal threshold to mute output

Question asked by audiolab1 on Apr 23, 2012
Latest reply on Jul 5, 2012 by BrettG

I have an ADAU1701 based system with an op-amp input buffer and an output stage after the DSP so that the entire chain is unity gain. Hence the output stage has a gain of just over 6dB to bring the 0.9Vrms output of the DSP to 2.0Vrms with a 2.0Vrms input signal. Connected to higher gain amplifiers, the steady state noise floor is quite high. What I would like to do is mute the signal inside the DSP when the input signal drops below a certain threshold. I have read the thread thread below and have the mute working.

 

http://ez.analog.com/message/7669#7669

 

The problem is that the threshold will not work below a certain input level which is something around 10mV. The noise floor of the entire chain is around 35uV, so I want this threshold to be at the limits of audibility through a typical speaker, likely something around 500uV. You can see that I am a long way off from this target! Any ideas on how to improve the low level resolution of this signal detection method? I would also like the mute function to occur after a certain number of seconds but for the system to "wake up" again as soon as an input signal above the threshold is detected. Your help is greatly appreciated!

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