Clear[xStep];
xStep[n_] := 0 /; n <= 0;
xStep[n_] := 1 /; n > 0;
ListPlot[  Table[xStep[n], {n, 20}], PlotRange -> {0, 1.1}]
Clear[yStep];
yStep[n_] := 
  yStep[n] = 
   0.098 xStep[n] + 0.195 xStep[n - 1] + 0.098 xStep[n - 2] + 
    0.942 yStep[n - 1] - 0.333 yStep[n - 2];
yStep[-1] = yStep[0] = 0
ListPlot[  Table[yStep[n], {n, 20}], PlotRange -> {0.0, 1.1}]
ListPlot[  Table[yStep[n], {n, 20}], PlotRange -> {0.90, 1.07}]

(* Explanation of xSine. A sine wave with frequency f can be described by the function sin(2\[Pi] f t), where t is the time in seconds. If we sample this function with a sampling rate s (s times per second), we can discretize the time as t = n/s, where n=0,1,2, \[Ellipsis] is an integer representing the index of the sample. If the sampling rate is s=8000 Hz, n=8000 corresponds to the time 1 second. In the definition below s is written as samplingRate. *)

Clear[xSine];
samplingRate = 
  8000.;  (* This is how often the signal is sampled. Do not change! *)

xSine[freq_, n_] := Sin[2 Pi  freq  n/samplingRate];
x[n_] := Sin[2 Pi  freq  n/samplingRate];
ListPlot[  Table[xSine[500, n], {n, 30}]]

Clear[y];
y[freq_, n_] := 
  y[n] = 0.098 xSine[freq, n] + 0.195 xSine[freq, n - 1] + 
    0.098 xSine[freq, n - 2] + 0.942 y[n - 1] - 0.333 y[n - 2];
y[0] = y[-1] = 0

yList = ListPlot[  Table[y[400, n], {n, 30}], PlotRange -> {-1, 1}]