Problem with resample and differentiation

Previously differentiated groove undulation of sine wave look good, however,
the entire differentiated signal shows low-frequency radius modulation and reflects in the resulting sound.


Audio (left, right channel by inner/outer differentiated radius)

http://kakyoism.webhop.net/~kakyo/0.report/41.wrong_diff/audio_mitac_stereo_v2.wav



Plot of left channel stereo (Silence), not scaled according to the right
x-y size ratio

http://kakyoism.webhop.net/~kakyo/0.report/41.wrong_diff/diff_silence.png



Plot of right channel stereo (1kHz Sine), not scaled according to the
right
x-y size ratio

Warning: This may not make much sense to eyes, just as a reference

http://kakyoism.webhop.net/~kakyo/0.report/41.wrong_diff/diff_sine.png

There are two possible causes:
1. This differentiation was done with Order 1 (every neighboring samples). There could be local errors here and there. But this doesn't explain well the fact that the error shows an overall trend of a low-frequency component.
2. The cause can be the disc center estimation error, which leads to the periodic error curve in the polar coordinates of the grooves. Haber tried to solve the similar problem by modelling the disc center with a sine-based center correction function. I may need to try that. However, this means to spend about 1-2 days on each try because the coordinates and groove edges are going to be regenerated. We need to think of better ways.

The clicks in the signal can be seen in the plotted differentiated signal. They can probably be filtered out with an additional low-pass filter. But I will delay this step until I solve the problem above.