multichannel signal envelope output format

Hi,

I am using the multichannel signal envelope on an adau1761, which I believe gives me the mean-squared signal. After this block I am using a readback to retrieve the mean-squared value which I want to use to get the root mean square value. The formula I have been using is:

rms_db = 20 * LOG10( SQRT( readback_val / ( 2^23 - 1 ))) (adau1761 uses Q5.23 format)

However my RMS value does not seem to be correct using the above formula. If I instead use this:

rms_db = 20 * LOG10( SQRT( readback_val / ( 2^19 - 1 ))) (which implies that the signal envelope block outputs Q5.19 format) I seem to get the correct value.

Does the signal envelope output Q5.19 format or should I look elsewhere for an explanation?

Regards,

Danny

Audio Signal Processors

SigmaDSP Audio Processors

adau1761