Arnie.d said:
A comb filter removes the rainbowing.

No, a comb filter separates the luminance (y) and chrominance (c) elements of a composite video signal.

Since video is stored on laserdisc in analogue composite form, there must be a comb filter somewhere in the chain.

A poor comb filter will lead to dot crawl and "rainbows" (aka cross-colour effects). A good quality comb filter will reduce the appearance of these effects.

Since the player the OP used does not (I think) have an s-video output, he would have hooked it up with a composite video cable, therefore the (cheap?) comb filter in the capture card will be used.

If the card has an s-video input, then a potential improvement could be obtained by connecting the LD player to the DVD recorder with a composite cable, then the DVD recorder to the capture card with an s-video cable. This uses the comb filter inside the DVD recorder, which is likely to give higher quality results.