On 10/01/18 18:53, Andy Walls wrote: [snip] >> When working correctly, the amplitude/frequency response should be >> within, ideally, 0.1 dB of the values shown. I've shown values for >> both 75 and 50 microsecond time constants. >> >> Freq (Hz) Gain dB (75us) Gain dB (50us) >> >> 30 0.00 0.00 >> 300 -0.09 -0.04 >> 500 -0.23 -0.11 >> 1000 -0.87 -0.41 >> 3000 -4.77 -2.76 >> 5000 -8.16 -5.40 >> 8000 -11.82 -8.64 >> 10000 -13.65 -10.36 >> 12500 -15.52 -12.15 >> 15000 -17.07 -13.65 >> > > FWIW, the attached plots compare the 50 us de-emphasis filter response > of GNURadio 3.7.10 vs. the numbers you provided.
FWIW they are not my numbers, but appeared to come from a reliable source. > The filters stay within 0.1 dB of each other up through 5000 Hz, but by > then your tabular response has noticeably started to bend upward. The > difference between the two filters is 3.44 dB at 15000 Hz. It bends up because your plot has got one log axis and one linear one. If plotted with a log frequency axis rather than a linear one then the slope at the right should tend to a straight line of 6.02 dB/octave or 20 dB/decade. Indeed the idea of dB/octave or dB/decade only makes sense if you use a log frequency axis. Alternatively, you could use a linear voltage axis instead of dB, and a linear frequency axis. That should also tend towards a straight line on the right hand side. -- Richard Lamont _______________________________________________ Discuss-gnuradio mailing list [email protected] https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
