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From: ikerr on 24 Apr 2010 21:47 Greetings, I have been reading through the ITUR BS.17701 (http://webs.uvigo.es/servicios/biblioteca/uit/rec/BS/RRECBS.17701200709I!!PDFE.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 ITUR BS.17701 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: 2.08333e05 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
From: ikerr on 25 Apr 2010 10:30 >Greetings, > >I have been reading through the ITUR BS.17701 >(http://webs.uvigo.es/servicios/biblioteca/uit/rec/BS/RRECBS.17701200709I!!PDFE.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 ITUR BS.17701 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: 2.08333e05 >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 xaxis has units of radians/second while the plot published in ITUR BS.1770 has units of Hertz along the xaxis. Converting to the appropriate units gave the desired results. Ian

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