Greetings, I have been reading through the ITU-R BS.1770-1 (http://webs.uvigo.es/servicios/biblioteca/uit/rec/BS/R-REC-BS.1770-1-200709-I!!PDF-E.pdf) document and have been trying to reproduce the frequency response of the RLB weighting using the supplied filter coefficients. However, when I use the supplied filter coefficients to construct a Bode plot in octave, the resulting plot attenuates more quickly than the one shown in Figure 4. At 10 Hz, the attenuation is about -55 dB in my octave plot whereas the attenuation is about -24 dB in Figure 4 of the ITU-R BS.1770-1 document. Here is the sequence of octave instructions that I am using: octave:84> fs = 48000; octave:85> a = [1 -1.99004745483398, 0.99007225036621]; octave:86> b = [1 -2 1]; octave:87> sys = tf(b, a, 1 / fs); octave:88> sysout(sys) Input(s) 1: u_1 Output(s): 1: y_1 (discrete) Sampling interval: 2.08333e-05 transfer function form: 1*z^2 - 2*z^1 + 1 -------------------------- 1*z^2 - 1.99*z^1 + 0.99007 octave:89> bode(sys) I'm trying to figure out what I'm doing wrong, however, thus far it is eluding me. Can someone point me in the right direction? Thanks, --Ian

# RLB Weighting

Started by ●April 24, 2010

Reply by ●April 25, 20102010-04-25

>Greetings, > >I have been reading through the ITU-R BS.1770-1 >(http://webs.uvigo.es/servicios/biblioteca/uit/rec/BS/R-REC-BS.1770-1-200709-I!!PDF-E.pdf) >document and have been trying to reproduce the frequency response of the >RLB weighting using the supplied filter coefficients. However, when Iuse>the supplied filter coefficients to construct a Bode plot in octave, the >resulting plot attenuates more quickly than the one shown in Figure 4.At>10 Hz, the attenuation is about -55 dB in my octave plot whereas the >attenuation is about -24 dB in Figure 4 of the ITU-R BS.1770-1 document. >Here is the sequence of octave instructions that I am using: > >octave:84> fs = 48000; >octave:85> a = [1 -1.99004745483398, 0.99007225036621]; >octave:86> b = [1 -2 1]; >octave:87> sys = tf(b, a, 1 / fs); >octave:88> sysout(sys) >Input(s) > 1: u_1 > >Output(s): > 1: y_1 (discrete) > >Sampling interval: 2.08333e-05 >transfer function form: >1*z^2 - 2*z^1 + 1 >-------------------------- >1*z^2 - 1.99*z^1 + 0.99007 >octave:89> bode(sys) > >I'm trying to figure out what I'm doing wrong, however, thus far it is >eluding me. Can someone point me in the right direction? > >Thanks, >--Ian > > >Indeed it was a simple mistake. The octave bode plot's x-axis has units of radians/second while the plot published in ITU-R BS.1770 has units of Hertz along the x-axis. Converting to the appropriate units gave the desired results. --Ian