Hiya and thanks for all the suggestions here is where I am up to: Guitar in Pad om/off - no difference
Aux in - Much better but still there
Return 1 in - As Guitar in
I have played with SPDIF output levels and that does make a difference but the signal gets so quiet it's verging on unusable and adding the Input Gate does little to help I then decided to put my base though a SansAMP Bass Driver DI into the Mic Input of the Helix to see if that would tame a hot signal and to an extent it has but it is still there in the low frequencies like it's overdriving something but the input levels to the SPDIF in are all in the green as well as the input levels in the DAW. I tried the SansAmp DI in both on and off modes and off mode was the best so far with an acceptable signal level. Solution: Guitar In (pad on) to 1/4" out no distortion So I guess that the SPDIF circuit is, in some way, getting too much of a hot signal at either my Focusrite or the Helix and as I don't have another SPDIF A/D converter to hand it will remain an unknown for the present moment. Many thanks for all your suggestions and patience.