function [stop_atten stop_band_start minus_3db] = measure_filter (f, atten) spec_len = 400000 ; # Calculate the spectrum. spec = 20 * log10 (abs (fft ([f zeros(1, spec_len - length (f))]))) ; spec = spec (1:spec_len/2) ; #-------------------------------------------------------------------------------# Find the first null which starts off the stop band. first_null = 0 ;for k = 2:length (spec) - 1, if spec (k) < -0.8 * atten && spec (k-1) > spec (k) && spec (k) < spec (k + 1), first_null = k ; break endif endfor #-------------------------------------------------------------------------------# Find the stop band minimum attenuation. stop_atten = max (spec (first_null:length (spec))) ; #-------------------------------------------------------------------------------# Find the x position on the transition band which has the same attenuation. atten_start = 0 ;for k = 1:first_null, if spec (k) > stop_atten && spec (k + 1) < stop_atten, atten_start = k ; break ; endif endfor atten_start = atten_start - 1 ; # Arrays are 1 based so subtract 1. stop_band_start = atten_start + (stop_atten - spec (atten_start)) / (spec (atten_start+1) - spec (atten_start)) ; stop_band_start = stop_band_start / spec_len ; #-------------------------------------------------------------------------------# Find -3db point. minus_3db = 0 ;for k = 1:first_null, if spec (k) > -3.0 && spec (k + 1) < -3.0, minus_3db = k ; break ; endif endfor minus_3db = minus_3db - 1 ; # Arrays are 1 based so subtract 1. minus_3db = minus_3db + (stop_atten - spec (minus_3db)) / (spec (minus_3db+1) - spec (minus_3db)) ; minus_3db = minus_3db / spec_len ; endfunction # Do not edit or modify anything in this comment block.# The arch-tag line is a file identity tag for the GNU Arch # revision control system.## arch-tag: cc2bc9a2-d387-4fed-aa0a-570e91f17c99
function [stop_atten stop_band_start minus_3db] = measure_filter (f, atten)
spec_len = 400000 ;
# Calculate the spectrum.
spec = 20 * log10 (abs (fft ([f zeros(1, spec_len - length (f))]))) ;
spec = spec (1:spec_len/2) ;
#-------------------------------------------------------------------------------
# Find the first null which starts off the stop band.
first_null = 0 ;
for k = 2:length (spec) - 1,
if spec (k) < -0.8 * atten && spec (k-1) > spec (k) && spec (k) < spec (k + 1),
first_null = k ;
break
endif
endfor
#-------------------------------------------------------------------------------
# Find the stop band minimum attenuation.
stop_atten = max (spec (first_null:length (spec))) ;
#-------------------------------------------------------------------------------
# Find the x position on the transition band which has the same attenuation.
atten_start = 0 ;
for k = 1:first_null,
if spec (k) > stop_atten && spec (k + 1) < stop_atten,
atten_start = k ;
break ;
endif
endfor
atten_start = atten_start - 1 ; # Arrays are 1 based so subtract 1.
stop_band_start = atten_start + (stop_atten - spec (atten_start)) / (spec (atten_start+1) - spec (atten_start)) ;
stop_band_start = stop_band_start / spec_len ;
#-------------------------------------------------------------------------------
# Find -3db point.
minus_3db = 0 ;
for k = 1:first_null,
if spec (k) > -3.0 && spec (k + 1) < -3.0,
minus_3db = k ;
break ;
endif
endfor
minus_3db = minus_3db - 1 ; # Arrays are 1 based so subtract 1.
minus_3db = minus_3db + (stop_atten - spec (minus_3db)) / (spec (minus_3db+1) - spec (minus_3db)) ;
minus_3db = minus_3db / spec_len ;
endfunction
# Do not edit or modify anything in this comment block.
# The arch-tag line is a file identity tag for the GNU Arch
# revision control system.
#
# arch-tag: cc2bc9a2-d387-4fed-aa0a-570e91f17c99