I have a data plot XY that goes from (X 0-127, Y -70.0 - 6.0 db)
Im using the 5th order polynomial function from plotting this data on this site [http://www.zizhujy.com/en-us/Plotter][1]
However, its not accurate at all at the top end (comes out at 8.5 db when it should be 6 db)
Is there any way of getting a more accurate curve (especially at the top end)? I cant use any more than 5th order polynomial (im using it in a development environment and can only input a set amount of characters)
[1]: http://www.zizhujy.com/en-us/Plotter db
0 -100
1 -78
2 -66
3 -59
4 -54
5 -50
6 -47
7 -44
8 -42
9 -40
10 -38
11 -36
12 -35
13 -33
14 -32
15 -31
16 -30
17 -29
18 -28
19 -27
20 -26
21 -25
22 -24
23 -24
24 -23
25 -22
26 -21
27 -21
28 -20
29 -20
30 -19
31 -18
32 -18
33 -17
34 -17
35 -16
36 -16
37 -15
38 -15
39 -14
40 -14
41 -13
42 -13
43 -13
44 -12
45 -12
46 -11
47 -11
48 -11
49 -10
50 -10
51 -9.7
52 -9.4
53 -9
54 -8.7
55 -8.4
56 -8.1
57 -7.8
58 -7.5
59 -7.2
60 -6.9
61 -6.6
62 -6.3
63 -6.1
64 -6.1
65 -6.1
66 -6.1
67 -6.1
68 -6.1
69 -6.1
70 -5.2
71 -4
72 -3.7
73 -3.5
74 -3.3
75 -3
76 -2.8
77 -2.6
78 -2.4
79 -2.1
80 -1.9
81 -1.7
82 -1.5
83 -1.3
84 -1.1
85 -0.9
86 -0.7
87 -0.5
88 -0.3
89 -0.1
90 0.1
91 0.3
92 0.5
93 0.7
94 0.8
95 1
96 1.2
97 1.4
98 1.6
99 1.7
100 1.9
101 2.1
102 2.2
103 2.4
104 2.6
105 2.7
106 2.9
107 3.1
108 3.2
109 3.4
110 3.5
111 3.7
112 3.9
113 4
114 4.2
115 4.3
116 4.5
117 4.6
118 4.8
119 4.9
120 5
121 5.2
122 5.3
123 5.5
124 5.6
125 5.7
126 5.9
127 6
You can do it with the zizhujy.com/en-us/Plotter : checkbox "Logarithm fit" (see the result below, very closed to my own result) But this program cannot compute the parameter $c$ . So, I added $c=0.3$ to the input $x$ data. (without a more sophisticated software, anyway you can approximate $c$ by groping).