SPDIF issue

I use Sonar 8.5 with my Lynx TWO, until today inputting guitar and bass via a Line6 TonePort UX2 via SPDIF into the Lynx card.

(I do this because Sonar can only use one ASIO device at a time, and I don't like switching between ASIO devices to play guitar then to record other instruments which go through the Lynx analog inputs.)

Today I noted that a guitar solo took on pops when EQ plugins were applied to it.  I had never noted this before, but it may be that the soft jazz guitar sound (with minimal treble grit) let me hear it for the first time.  I use Waves and Sonnox plugins of the highest quality.

I froze the tracks and looked carefully at the waveforms and sure enough there were spikes atop the waveform peaks in various places -- sharp vertical-only spikes that were absent prior to the EQ addition.  These little spikes appeared like shark fins across 10% of the top of the composite waveforms.

Needless to say, I thought it was an artifact of the processing burden, and increased latency and buffers and all that to see if it would go away.  It did not.  I then began to wonder "could the pre-processed waveform have some inherent flaw in it that is brought out by processing?".  There were no clicks or peaks in the native waveforms prior to processing.

So I went to a keyboard track that I had recorded via the Lynx analog inputs.  I processed it the same way and heard and saw nothing of these odd glitches.

I then setup two tracks in Sonar, with one recording the guitar via the Lynx analog inputs and one recording via the SPDIF input.  I then added identical EQ plugins to each track and listened to them.

The SPDIF track popped and clicked as noted before; the analog track was pristine.

Any ideas why this might occur? 

As well, the SPDIF track was OUT OF PHASE  with the analog track.

I would love to understand this.  Thanks for any responses!

Jon 

Clicks on an S/PDIF-recorded track are an indication that S/PDIF was not selected as the clock source for the interface.