RMS Table range

tommi Question

Mar 7, 2012 00:00

Hello,

I'm experiencing some unexpected results from a RMS Table block inside a Sigma (3.1) DSP project for 1701.

What is the table output for signals exceeding +6dB RMS amplitude?

Is it the clipped to the highest value set inside the table or is it mapped back to 0?

Thanks a lot in advance.

rms

exceed

range

table

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full

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ADIApproved Reply

Apr 9, 2012 00:00

Hi Tommi,

Sorry for the late response. I was out of the office frequently over the past several weeks.

The RMS Table uses some interpolation between points and it relies on the input not exceeding the +6 dB level in order to work properly. The performance of the RMS Table for values outside of this range varies by device.

At the moment I don't have hardware available so I can't test this until later this week, but I believe the current implementation of the RMS table for the ADAU1701 extrapolates the highest point in the table and uses that for higher inputs. However, that was a fix that was made sometime during the 3.x revisions. With 3.1 you might have an earlier version of the algorithm that had no way to account for inputs over the +6 dB limit.

By the way, I'm just curious... Is there a particular reason you are sticking with version 3.1 instead of updating to a more recent version of SigmaStudio? Version 3.1 is already several years old.

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tommi Reply

Apr 10, 2012 00:00

Hi Bret, thank you for your reply.

I will check the Table's behaviour in later versions.

By now we have to stick to version 3.1 because the function library we are using to manage the ADAU1710 inside our products is written to parse .hex files as they were written by that version.

We had experienced some incompatibility issues with .hex files generated by later versions and did not yet have the time to plan an update of the library.

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