ADAU1761 Frequency Response and Missing Items in SigmaStudio Toolbox

Hi, all.

Two questions:

1) We have been testing the ADAU1761 in a new product. We have a mystery in that if we set up the SigmaStudio white noise generator and connect it straight to one (or both) of the outputs, the observed spectrum at the output is not quite flat. The output level at 100Hz rises steadily by about 3dB to 3KHz. Above 3KHz it is flat.

But if we use a SigmaStudio sine generator and check spot frequencies, the level at the output is pretty much flat across the spectrum. Is this a feature of the white noise source or am I missing something? I have tried the same dsproj on the ADAU1761Z demo board and it behaves the same way. In neither case am I loading anything in a way that would cause coupling caps to create L.F. roll-off.

2) Silly question, but SigmaStudio 4.5 no longer appears to have "Add" available in the "Basic DSP" tools. We occasionally use this, for example to add an offset to the sawtooth generator, to create a swept sine wave with the VCO. There are obviously ways around it, but they just seem a little messy.

Thanks in advance,

Alex

Audio Signal Processors

SigmaDSP Audio Processors

adau1761