Re: [Discuss-gnuradio] voltage pulse from UHD driver

[Marcus D. Leech]

On 01/15/2015 12:40 PM, Nick Foster wrote:
> Second, there are digital halfband and CIC filters in the USRP, and 
> they are not reset between acquisitions. This means that the first 
> samples will have some junk left over from the last acquisition.
If the filters were "reset", what would they be reset *to*?   You have 
no way of knowing what is about to arrive from the ADC, so ANY 
"pre-load" values you put in the pipeline are necessarily going to be 
garbage of one kind or another, so there will *always* be a startup 
transient.  It's as inevitable as the Sun
coming up in the morning, or Starbucks selling you a way-too-expensive 
cup of coffee with your name mis-spelled on it :)

This kind of thing nearly always comes as a shock to folks who might be 
encountering real-time signal processing of the analog/physical world.
  Ones "mental model" of the ways things work is usually slightly 
defective in that it thinks in terms of "steady-state behavior".

Similar things can be seen in quite-ordinary consumer-level broadcast FM 
receivers, for example.  The digitally-tuned PLL receivers will almost 
*always*
  mute the audio between station changes, because "ugly stuff is 
happening".  This is exactly the same thing.