DFD Processing State Initialization

[TaylorG]

Hey maxwellb,

Try replacing your DFD NStage MRate Filtering with State with simply the DFD NStage MRate Filtering VI.  You can create a True Constant and set the init? (F) to TRUE for your first case, then have it as FALSE for the remaining iterations.  Let me know if that helps!

[maxwellb]

Taylor,

I actually have tried that, and the effects are almost exactly the same.

[TaylorG]

What sort of filter configurations do you have feeding in to the DFD NStage MRate Filtering with State.vi?

[TaylorG]

After doing some research, what is most likely causing this unwanted artifact is the natural transient response for digital filters.  There's a great article and example at the link below that explains the transient response for a digital filter and why it takes some time for the signal to settle down to its steady state.  If you get a chance, run through the article and example and let me know if this helps!

Filter Transient

[maxwellb]

Taylor,

This article does describe something similar to my problem. That is encouraging to see. However, it doesn't mention any solutions.

Is this just a problem that digital filters will always have? I thought there must be some way to initialize the filter correctly and avoid the initial transient.

[TaylorG]

When using digital filters, it is my understanding that there will always be a transient state that the output signal will go through before it reaches its steady state.  However, depending on what type of filter you use (Finite Impulse Response or Infinite Impulse Response), that transient response can vary based on filter orders and feedback coefficients.  As you can see in that example, the transient response varies if you change the filter type and the filter order.  Hope this helps!