Multiple Sub-Nyquist Sampling Encoding - History

History

MUSE, a compression system for Hi-Vision signals, was developed by NHK Science & Technology Research Laboratories in the 1980s, employed 2-dimensional filtering, dot-interlacing, motion-vector compensation and line-sequential color encoding with time compression to 'fold' an original 20 MHz source Hi-Vision signal into a bandwidth of 8.1 MHz.

• Japanese broadcast engineers immediately rejected conventional vestigial sideband broadcasting.
• It was decided early on that MUSE would be a satellite broadcast format as Japan economically supports satellite broadcasting.

Modulation research

• The idea of frequency modulation of a conventionally constructed composite (Y+C, like NTSC and PAL) signal was first tested. This was called the HLO-PAL system which used a Phase Alternating by Line with Half-Line Offset carrier encoding of the wideband/narrowband chroma components. Only the very lowest part of the wideband chroma component overlapped the high-frequency chroma. The narrowband chroma was completely separated from luminance. HLO-PAF, with Phase Alternating by Field (like the first NTSC color system trial) was also experimented with, and gave much better decoding results, but NHK abandoned all composite encoding systems when work on dot-interlaced (a.k.a. sub-Nyquist) encoding was started. As an interesting side-note, RCA's original 1949 (and FCC rejected) compatible color TV system proposal used horizontal dot-interlacing as a method of encoding the R-G-B color components, as did a variation of the CBS Field-Sequential color system - CBS proposed horizontal dot-interlacing in a desperate attempt to increase horizontal resolution. In television, frequency-interlacing, such as is done with the chroma/luma components in NTSC and PAL color, automatically leads to dot-interlacing - but in those cases, the interlacing is in the vertical direction. Without digital field storage of some sort for playback, horizontal dot-interlacing leads to too much shimmer, dot-crawl, field-flicker and spurious dot-patterns to make the process useful. And it only leads to about a .50% increase in actual resolution.
• Separate transmission of Y and C components was explored. The MUSE format that is transmitted today uses separated component signalling. The improvement in picture quality was so great that the original test systems were recalled.
• One more power saving tweak was made: Lack of visual response to low frequency noise allows significant reduction in transponder power if the higher video frequencies are emphasized prior to modulation at the transmitter and de-emphasized at the receiver.