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ADAU1761 - Maximising dynamic range of compressor

Question asked by JohnAmpetronic on Jan 10, 2014

Hi All


I wonder if anyone could give me an idea how to maximise the dynamic range of the ADAU1761?  ADC noise is worse when dealing with low level signals that are only exercising the lower LSBs of the ADC.  So for low level signals it is good to apply analogue gain before the ADC.  However this overloads the ADC for higher signal levels.  What I want is a compressor that controls the PGA amplifier as well as processing in the digital domain.


This post describes how to vary the input gain of the PGA from with the digital domain.


Further tests have shown that the output number in 5.23 format to the AIGC of the PGA amplifiers results in logarithmic control of the amps.

Value     Gain

1               200

0.9            123

0.8           70.3

0.7          41.9

0.6          24

0.5          14.1

0.4          7.9

0.3          4.58

0.2          2.6

0.1          1.5


What I would like to do is to maximise the range of the compressor by varying the analogue amplifier gain as well as controlling through the digital algorithm.  In other words linking the two together.  If the compressor was written in assembler it would be easy - select the appropriate gain for the input signal level and make up the rest with digital gain/attenuation.  However all my attempts to do this in SigmaStudio have changed the compressor characteristics. 


Any pointers as to how to go about this?  Do I need to design the whole compressor from basic SigmaStudio blocks?