I`ve fed the source a 0dbfs 1kb tone
set the full scale voltage according to that number
The 0 dBFS tone is being generated by what device?
Its a cd run through the head unit that I`m measuring. The cd was recorded @ odbfs according to the liner notes.
So, in SignalScope, you tweaked the user-defined full-scale voltage until the oscilloscope indicated a level of 0.73 Vrms on the appropriate input channel. What full-scale voltage did you settle on?
I settled on 1.650 volts.
Getting the same reading suggests that you could be clipping on the input channel and that you are reading a peak voltage (Vpk) rather than an rms voltage (and that your full-scale voltage is incorrect).
Yeah the more I think about it the more I`m convinced my full scale voltage is wrong ( I think I read peak to peak as you suggest)which is something that I can fix. What worries me is clipping the inputs of my Mbox2 and if I am I dont know how to prevent that from happening.
What does the waveform look like in the oscilloscope?
I guess its a bit squared not fully squared though.