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Strange result from small addition to an existing project

Question asked by KJBob on Oct 1, 2012
Latest reply on Nov 12, 2012 by KJBob

Hi,

 

     My overall project has been though many revisions, growing to near the ADAU1701's capacity.  After adding the two blocks circled below,  instead of normal output the three used DACs  all produce a shrill white noise.SigmaDSP.jpg

The instruction count after the addition is 1008 (still OK).  The added blocks are not in the audio path at all, instead they're intended to improve the performance of a tone decoder.  Removing the offending blocks restored normal operation.

 

     To troubleshoot I cut and pasted the tone decoder into several tiny projects with only a few other blocks, with inconsistent results. For example, the schematic below did not work (made the white noise) until I deleted the circled blocks (replacing them with a direct audio path).  Compiling-downloading  without these blocks stopped the white noise.  Then I clicked the undo button a few times to restore these blocks, and compiled-downloaded again.  Unlike just previously, this time the same schematic did not make the noise.  The attenuator output is shown feeding a null T rather than the desired signal_add, as sometimes this change itself stopped the white noise (but not at first).

SigmaDSP3.jpg

     After installing the latest beta version of SigmaStudio, I rebuilt the small project with the tone decoder from scratch (not cutting and pasting from the full project this time).  This version works.  Somehow I remember running into the same white noise when adding stuff to my main project some months ago, when it was a lot smaller than it is now.  I also worked around it then  by redrawing the project without all the additions, deletions, and tests the original project file went through.  Then I could continue on.  I'd hate to have to redraw my entire project now, however, it would take a whole day.  Anyone else had this problem?  Is there an easier fix?

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