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.
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