1.       
  2.  
  3. Manipulate[
  4.  (*Nasser M. Abbasi, June 20, 2014*)
  5.  (*the signal is cosine, and the SNR is given as ratio of variances*)
  6.  Module[{nPoints, x0, varx0, n, x, del},
  7.   nPoints = 128;
  8.   del = 4 Pi/(nPoints - 1);
  9.   x0 = Cos[Range[0, 4*Pi, del]];
  10.   varx0 = Variance[x0];
  11.   SeedRandom[0];
  12.   n = RandomVariate[NormalDistribution[0, 1], nPoints];
  13.   x = x0 + Sqrt[varx0/snr]*n;
  14.   Show[ListLinePlot[x0, PlotStyle -> Blue], ListLinePlot[x, PlotStyle -> Red], PlotRange -> {{0, Round[xmax/del]}, {-ymax, ymax}}, 
  15.    ImagePadding -> {{40, 15}, {40, 40}}, Frame -> True, ImageSize -> 400, 
  16.    FrameLabel -> {{"y(t)", None}, {"time", "Adding noise to signal"}}, Axes -> None]
  17.   ],
  18.  Grid[{
  19.    {"SNR",
  20.     Manipulator[Dynamic[snr, {snr = #} &], {1, 999, 1}, ImageSize -> Tiny],
  21.     Dynamic@Row[{NumberForm[snr, 3], " (", NumberForm[10. Log[10, snr], 4], " db)"}]
  22.     },
  23.    {"x max",
  24.     Manipulator[Dynamic[xmax, {xmax = #} &], {.1, 4.*Pi, .1}, ImageSize -> Tiny],
  25.     Dynamic[xmax]
  26.     },
  27.    {"y max",
  28.     Manipulator[Dynamic[ymax, {ymax = #} &], {.1, 1.4, .1}, ImageSize -> Tiny],
  29.     Dynamic[ymax]
  30.     }
  31.    }, Alignment -> Left
  32.   ],
  33.  {{snr, 50}, None},
  34.  {{xmax, 4.*Pi}, None},
  35.  {{ymax, 1.4}, None}
  36.  ]