If the tape head is not set exactly identical to the setting when the tape
was recorded, playing it back in mono or through a surround system will
result in very ugly artifacts.
But even normal stereo playback may sometimes sound a bit unpleasant.
The cause of this is that the tape does not more over the tape head exactly
the same way as it did during recording, for example because the tape head
has moved (or a different cassette deck is used), or because the tape got
stretched a bit. Even very small tape or tape head displacements (20 μm = 0.02 mm difference between the left and right channel) can be audiable.
The AZIMUTH correction calculates the correct
tape head setting on the fly, and corrects for it, even if the tape head is
moving during playback (which occurs on some tape decks).
The AZIMUTH correction filter has two sliders:
This slider limits the maximum tape head 'displacement' that can be
detected and resolved.
Higher values cost more CPU power. Note that if the 'displacement' is
large, the sound quality for each channel will suffer, and this
cannot be solved by this filter. So if there is a constant and large
(more than 30 μm) displacement, better results can be achieved by
adjusting the tape head, as described in
Digitizing tapes: Tips for getting the best possible sound from your tapes.
change speed (μm/s)
This slider controls how fast the azimuth correction can change if the
measured displacement is differs from the correction that is taking
Use a very low value (≤ 0.1 μm) to correct for a constant azimuth correction.
Use a higher value (~ 0.4 μm) to also correct for rapid changes.
To avoid getting too much effects from measurement noise, use the lowest
possible value where the blue line (the actually performed correction)
can keep up with the red dots (the measurements).
This filter only works properly if the sounds at the left and right channel
are similar. If this is not the case for a longer period, the azimuth correction
will slowly be reduced.