De-emphasis: sharing some results
Reply #69 – 2011-08-29 15:50:11
The FIR I gave above came in at ~0.0007 dB absolute amplitude error; a little improvement in the filter design and I've now got it to < 0.00002 dB (with the same number of taps). The phase response should be equally good. So the filter should now give almost bit-perfect removal of an ideal emphasis filter, providing that the CD audio roll off is below that of the FIR (which seems to be the case at least for the TDSOTM and Abbey Road Japanese discs). Of course, in fact it doesn't matter either way: the spectrum above 20k is intended to be used for filter roll-off etc. E.g.sox input.wav output.wav fir deemph.fir where deemph.fir contains: -1.1920929e-07 2.3841858e-07 -4.7683716e-07 5.9604645e-07 -8.3446503e-07 1.0728836e-06 -1.3113022e-06 1.5497208e-06 -1.6689301e-06 1.6689301e-06 -1.5497208e-06 1.1920929e-06 -4.7683716e-07 -5.9604645e-07 2.1457672e-06 -4.1723251e-06 7.0333481e-06 -1.0490417e-05 1.4901161e-05 -2.0027161e-05 2.6106834e-05 -3.2901764e-05 4.0531158e-05 -4.8875809e-05 5.7578087e-05 -6.6518784e-05 7.5340271e-05 -8.3565712e-05 9.0837479e-05 -9.6678734e-05 0.00010025501 -0.00010097027 9.8228455e-05 -9.1314316e-05 7.9274178e-05 -6.1511993e-05 3.7431717e-05 -6.4373016e-06 -3.194809e-05 7.8201294e-05 -0.00013208389 0.0001938343 -0.00026285648 0.00033855438 -0.00041997433 0.00050568581 -0.0005941391 0.00068318844 -0.00077056885 0.00085330009 -0.00092864037 0.00099301338 -0.0010430813 0.0010749102 -0.0010849237 0.0010690689 -0.0010237694 0.00094544888 -0.00083076954 0.00067675114 -0.00048112869 0.00024199486 4.1842461e-05 -0.00037062168 0.00074386597 -0.0011600256 0.0016168356 -0.0021107197 0.0026370287 -0.003190279 0.0037635565 -0.0043493509 0.0049386024 -0.0055214167 0.0060870647 -0.0066232681 0.0071167946 -0.0075529814 0.0079151392 -0.0081838369 0.0083357096 -0.0083402395 0.0081554651 -0.007717371 0.0069189072 -0.0055570602 0.0031843185 0.0014334917 -0.013371706 0.43148828 0.24382663 0.10041237 0.10355854 0.032810807 0.049596071 0.0059109926 0.026768446 -0.0037311316 0.016291976 -0.0063681602 0.010832548 -0.0062408447 0.0074832439 -0.0050983429 0.0051006079 -0.0036728382 0.0032455921 -0.0022794008 0.0017566681 -0.0010566711 0.00057590008 -6.3419342e-05 -0.00032174587 0.00068235397 -0.00095629692 0.0011872053 -0.001352787 0.001473546 -0.0015434027 0.001573801 -0.001565814 0.0015269518 -0.0014607906 0.0013736486 -0.0012694597 0.0011531115 -0.0010290146 0.00090098381 -0.0007724762 0.00064647198 -0.00052559376 0.00041174889 -0.0003067255 0.0002117157 -0.00012743473 5.4240227e-05 7.7486038e-06 -5.877018e-05 9.9420547e-05 -0.00013017654 0.00015211105 -0.00016593933 0.00017285347 -0.00017368793 0.00016975403 -0.00016188622 0.00015103817 -0.00013816357 0.00012385845 -0.0001090765 9.4056129e-05 -7.9631805e-05 6.5922737e-05 -5.3167343e-05 4.1842461e-05 -3.1709671e-05 2.3126602e-05 -1.5854836e-05 9.894371e-06 -5.1259995e-06 1.5497208e-06 1.1920929e-06 -2.9802322e-06 4.1723251e-06 -4.6491623e-06 4.8875809e-06 -4.7683716e-06 4.2915344e-06 -3.8146973e-06 3.3378601e-06 -2.7418137e-06 2.1457672e-06 -1.6689301e-06 1.1920929e-06 -8.3446503e-07 5.9604645e-07 -3.5762787e-07 2.3841858e-07 -1.1920929e-07