Readback cell format and value appear /10 out?

Brettcoupe Question

Oct 26, 2010 00:00

Hi.

I am using a readback cell attached to a peak env detector

and using the

dB_value = 96.32959861 * ((readback_value / 2^19) - 1)

My cell is set to output 5.19 format. if I am reading by control port can you set the format? or is it fixed on the 1940 ic

I am seeing that the result db_Value is divide by 10 what at real measure level is

So 0dbfs outputs 0 ok

but -10dbfs outputs -96 limit of resolution

Hence -0.1dbfs outputs -1.

Question 1. The value readback, Is that the raw readback register values Or is it some linear representation of it as a float 5.19?

Thanks

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Brettcoupe Reply

Oct 28, 2010 00:00

I worked out what is going on

The readback via the control port is always 24.0 format. regardless of what format you select in the sigma studio

I then used the formula

Lin_value = ((float)readback_value / 524288) ; // convert to linear below fs

Then if you want dBFs

dBfs= 20 * log10(Lin_value) ; // convert to dbfs

Thanks

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ADIApproved Reply

Oct 28, 2010 00:00

A more accurate description would be "24 bits are read back and the least significant 4 bits are truncated." However, it's difficult to say what these 24 bits actually represent because that depends on what signal or coefficient they are attached to. It all has to do with number formats. A more detailed description is in this thread:What are the number formats for SigmaDSP?. I hope that clears up some confusion.

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EZAdministrator Reply

Aug 2, 2018 00:00

This question has been assumed as answered either offline via email or with a multi-part answer. This question has now been closed out. If you have an inquiry related to this topic please post a new question in the applicable product forum.

Thank you,
EZ Admin

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