# A-weighted filtering # Made by AudiTon (auditon@xs4all.nl) october 2007 # 1st order high pass and 1st order low pass sections in cascade # result: 1. selected Sound A-weighted filtered accurately # 2. filter available as spectrum object (complex) # 3. function can be drawn if asked for # 4. filter can be made by analog hardware form A-weighted filter, made by 1st order lp and hp sections comment Select Sound object first! comment DFT is most accurate but can be slow choice Transfer_mode 1 button DFT button FFT boolean Plot_filter_gain_function yes endform t1 = 1.30516738e-5 t2 = t1 t3 = 7.7263443e-3 t4 = t3 t5 = 1.47841175e-3 t6 = 0.21569737e-3 # make base spectrum obj\$ = selected\$("Sound") if transfer_mode = 1 To Spectrum... no else To Spectrum... yes endif Copy... former # make modulus 1 Formula... 1/sqrt(2) # filters 1 and 2 (low pass) for i to 2 tc= t'i' call lowpass endfor # filters 3 .. 6 (high pass) for i from 3 to 6 tc= t'i' call highpass endfor # lift 2 dB for normalizing 0 dB at 1000 Hz (ref. ANSI) Formula... self*10^(2/20) Copy... filter # filter sound re\$="Spectrum_'obj\$'[1,col]" im\$="Spectrum_'obj\$'[2,col]" select Spectrum former call complexmult Rename... filtered To Sound if plot_filter_gain_function=1 select Spectrum filter # make unity gain ref. 0 dB in picture # When modulus = 1 then level = 94 dB SPL bin=Get bin width Formula... self*10^(-94/20)/sqrt(2*'bin') Draw (log freq)... 20 20000 -60 6 yes One mark left... 0 yes yes yes # adjust level back to normal for possible more filtering Formula... self*10^(94/20)*sqrt(2*'bin') endif # end procedure lowpass re\$="1/(1+(2*pi*x)^2*'tc'^2)" im\$="-2*pi*x*'tc'/(1+(2*pi*x)^2*'tc'^2)" call complexmult endproc procedure highpass re\$="(2*pi*x)^2*'tc'^2/(1+(2*pi*x)^2*'tc'^2)" im\$="2*pi*x*'tc'/(1+(2*pi*x)^2*'tc'^2)" call complexmult endproc procedure complexmult Copy... filter Formula... if row=1 then Spectrum_former[1,col]*'re\$'-Spectrum_former[2,col]*'im\$' ... else Spectrum_former[1,col]*'im\$'+Spectrum_former[2,col]*'re\$' fi select Spectrum former Remove select Spectrum filter Rename... former endproc