Linear-phase filtering for playback of recorded folded-spectrum

Details Linear-phase filtering for playback of recorded folded-spectrum Linear-phase filtering for playback of recorded folded-spectrum

1992-02-07

1994-10-11

Chin, Tommy P.

Facsimile and static presentation processing

Facsimile

Recording apparatus

358330, H04N 576

Patent

active

053552270

ABSTRACT:
An apparatus and a method for reproducing television images from recordings of folded-spectrum video signals uses a zero-crossing detector to convert an FM signal encoding folded-spectrum luminance signal to a PPM signal having the folded-spectrum luminance signal in its baseband, accompanied by the harmonics of the FM carrier and their respective sidebands. The PPM signal is digitized by an analog-to-digital converter, after passage through an anti-aliasing filter that is used to suppress only higher frequencies that would otherwise be sampled at less than Nyquist rate during digitization. Except for this anti-aliasing filtering, the suppression of the harmonics of the FM carrier and their respective sidebands is deferred until after digitization. Linear-phase digital filtering is then used to suppress the harmonics of the FM carrier and their respective sidebands, and the folded-spectrum luminance signal supplied in response to this digital filtering is unfolded to restore it to its original full bandwidth. This procedure permits the group delay characteristic below the folding-carrier frequency to be kept constant, thereby avoiding phase error as would interfere with the unfolding of the folded signal into the original full bandwidth.

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Howson et al., Reduction of Television Bandwidth by Frequency Interlace, Jul. 1, 1959.
Research disclosure (anonymous).

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