Audio Shield rev D with Teensy 4.1 output is low pass filtered!

[sw_hunt]

Function generator 1Vpp 10kHz sawtooth -> Shield line input -> Teensy -> Shield Line output -> 100MHz scope.
Shield plugged into Teensy by simple socket, so all connections less than 10mm. Nothing else connected apart from USB to PC.
Running Example sketch PassThroughStereo.
Using the scope to look at the input to the shield is a perfect crisp sawtooth. Looking at the output is very low pass filtered.
Hopefully a photo is attached...
Surely I should be getting the same crisp sawtooth at the output too?

 

[MarkT]

The input is sampled (at 44.1kSPS I think), processed digitally, and output with the DAC. Not many harmonics of 10k before Fs.

Figure 1 in the SGTL5000 datasheet show the signal routing in the chip - its seems the headphone output can bypass the digital
processing, don't know if Audio library supports that. The line output is DAC only though.

 

[sw_hunt]

Ah thanks MarkT, of course! I'm seeing a 10kHz sawtooth filtered to about 20kHz.

 

[jube]

@MarkT, it is not yet supported in Audio Library, but I added it in a PR a couple of months ago. https://github.com/PaulStoffregen/Audio/pull/334