The pulse is filled with a zero every nth sample.
n = 1-15
The filter can be adapted for other sample rates. It is now played back in slow motion. It may be unintuitive but try it. The filter with zeros added after every position (n=1) just acts an octave lower in pitch.
“Filterless” because the amplitude is incorrect and the brickwall filter has not yet been applied.
If we have an impulse with a 48kHz sample rate, using n=1 (zeros added after every position), our curve “slides” uniformly an octave lower. When playing back or working with a double sample rate of 96 kHz, the result is now correct again.
So you can change the sample rates of filters experimentally without the effect of the brickwall filter in the automatic sample rate conversion.