Identification of the delay induced by a FIR interpolator block in simulink

I am currently trying to upsample some signals in Simulink using the FIR interpolation block.

To test such functionnalities, I used the `ex_polyphaseinterp` example provided in the documentation.

According to the same documentation, with the settings used in the example, the interpolated signal should have a 3 sample delay (as the upsample factor is of 3).

However, when checking the scope for the signals, a much higher delay is observed as can be seen below

Can anyone clarify the information in the documentation and / or point errors in my reasoning ?

[Jyotsna Talluri]

Is it mentioned somewhere in documentation that the interpolated signal should have 3 sample delay?

[Guerin Nicolas]

@JyotsnaTalluri, In the latency section, it is stated that if the Elements as channels (sample based) input option is selected, and for a L interpolation factor the block has a latency of L samples. Hence my last question : Can anyone clarify the information in the documentation and / or point errors in my reasoning ?

[Mathieu NOE]

hello

I wonder if the term "latency" in the doc covers everything you see on your graph

beside this " latency " effect (to be clarified) , any FIR filter will show a group delay equals half of the FIR order

do you know your filter order ?

Answer 1

[Elady]

Hello Guerin,

The delay that you see in the FIR interpolator output is a result of the FIR group delay, like Mathieu mentioned.

That delay should not be confused with the latency discussed in the documentation. That latency has a different meaning, pertaining multirate execution and frame-based processing, which is not the case here (you verify that the FIR Interpolator block runs in "sample based" mode).

In the case of the ex_polyphaseinterp example, the FIR is obtained by h=fir1(35,0.3). It is a symmetric type-II linear phase FIR, which has a group delay of samples. Accounting for the sample time in the simulation, the expected output delay is , exactly as it shows on the scope.

Regards,

Elad