Utility functions for filter computations
| Name | Description | 
|---|---|
|  | Return coefficients of normalized low pass Bessel filter (= gain at cut-off frequency 1 rad/s is decreased 3dB) | 
|  | Transform filter to form with highest power of s equal 1 | 
|  | Compute correction factor of low pass filter such that amplitude at cut-off frequency is -3db (=10^(-3/20) = 0.70794...) | 
|  | Return alpha for band pass |