2003-09-19 20:39:09 UTC
Hi-Vision format that was used on LD's in the past, I thought I'd take
a moment to post the technical info about MUSE since, so far, the info
that has been posted has been either incomplete or flat-out wrong.
There are several versions of MUSE.
* Narrow MUSE
* MUSE-9 and
Japan's NHK, the main developer of MUSE, considers the MUSE-T and
MUSE-E formats to be "High-Definition," and the rest to be "Advanced
Definition." All of the MUSE formats start with the 60 MHz,
1125-line, 60fps, 2:1 Interlaced Hi-Vision studio production standard.
The luminance signal has a 30 MHz bandwidth and the Pr/Pb
color-difference signals each have a 15 MHz bandwidth . There are
1125 scan-lines per frame with 1035 active lines. Horizontal
luminance resolution, at the 3db point, is around 1200 lines. If
digitized, the Y signal has 1920 samples per line while the
color-difference signals have 960.
MUSE-T is the transmission studio transmission format, for field-pick
up, etc it has a 16.2 MHz signal bandwidth and uses Time Compression
Integration (a.k.a. Time Division Multiplexing) and field-offset
subsampling in which the phase of the sampling is inverted every
field. This reduces the transmission bandwidth to half that of the
original signal. Luminance resolution varies between stationary and
motion images. In a stationary region of the image, the diagonal
resolution is one-half, while in the motion regions, the horizontal
resolution is cut in half. For a stationary signal, the horizontal
bandwidths that can be transmitted with MUSE-T are 28 MHz for
luminance and 7 MHz for chrominance. Unlike in the NTSC system, MUSE
bandwidth does not correspond directly to horizontal resolution (i.e
80 lines per 1 MHz.) Like the other MUSE systems, MUSE-T uses the
Pseudo-Constant Luminance System for better high-frequency detail in
the Y signal. NTSC is theoretically a constant luminance system, but
gamma processing before Y-I-Q matrixing degrades high-frequency
MUSE-E. This is the system that most people are talking about when
they speak of "MUSE". It has been used for both DBS satellite
transmission to Japanese homes and for Hi-Vision MUSE LaserDiscs. The
MUSE-E system was developed for Hi-Vision broadcasting over a single
satellite channel and compresses the baseband high definition signal
to 8.1 MHz by a relatively simple technique with good image quality.
As the name suggests, MUltiple sub-Nyquist-Sampling Encoding (MUSE) is
a multiple subsampling encoding system. It performs subsampling twice
to compress the video signal into a bandwidth of 8.1 MHz.
The MUSE-E signal is based on TCI, which performs time division
multiplexing of the Y/C signal. The 48.6 MHz sampled TCI encoded
signal is then subjected to 24.3 MHz field offset, 32.4 MHz frame
offset and 32.4 MHz line offset sampling, with motion-vector
processing, to form a 16.2 MHz sampled, 8.15 MHz bandwidth encoded
signal. The Sub-Nyquist sampling "folds" higher frequency signals
down into the lower frequency spectrum via aliasing in the diagonal
dimension. Thus, diagonal resolution is reduced.
The MUSE signal also contains, in the vertical blanking period,
4-channel 15-bit Mode-A or 2-channel 16-bit Mode-B DANCE (Differential
PCM Audio Near-intantaneous Compressing and Expanding) encoded dignal
audio and independent data with a maximum bitrate of 1350 kb/s. In
both the satellite transmission system and the Hi-Vision LD format,
the 8.1 MHz MUSE-E signal is based on the analog transmission of
sampled values using PAM, Pulse Amplitude Modulation. In the LD
format, the PAM RF signal is stored as PWM on the disc itself.
The specifications for the MUSE-E system are good, for it's time, but
below today's digital HD systems. MUSE-E Horizontal luminance
resolution is 600-lines per-picture height, but only for stationary
images. For moving images, horizontal luminance resolution drops to
336-lines. In statonary images, diagonal luminance resolution is
one-half that of the horizontal. Chrominance resolution is around 500
lines for stationary signals and 240 for moving images. Actually,
chroma resolution varies a little bit more than this since, before
encoding, the color difference signals are separated into "wideband"
and "narrowband" signals, with the wideband Pr signal having a
pre-encoding bandwidth of 7 MHz and the narrowband Pb signal having a
bandwidth of 4 MHz.
Because MUSE-E is an analog system, it is VERY sensitive to jitter in
the received signal in the Hi-Vision LD format, a special pilot
signal is inserted to align the subsampling phase and control disc
rotation. In addition, it has all the other artifacts inherent in
the analog LD format; drop-outs, crosstalk, chroma noise,
high-frequency luma noise, etc.
Narrow MUSE. This is the "Advanced Definition" MUSE format that was
submitted to the ATSC for consideration as the American HDTV standard
and the only analog system to make it to the final round of testing
it performed quite poorly NHK was embarrassed by its performance.
Narrow MUSE is a simulcast, non-compatible system that uses a standard
6 Mhz wide channel. It was designed primarily for over-the-air
service in the United States. The 1125-line MUSE-E signal is the
basis for Narrow MUSE, and after MUSE-E pre-encoding, is translated
into a 750 scanning-line signal. The base bandwidth of the 750-line
Narrow MUSE signal is 4.86 MHz. Vertical luminance resolution is 650
lines. Horizontal luminance resolution is 500 lines
per-picture-height for stationary images and 325-lines PPH for moving
images. Chroma resolution varies from one-half to one-quarter the
luma resolution. Once modulated with sound, etc., the Narrow MUSE
signal occupies 5.946 MHz of the 6 MHz channel.
MUSE-6 & MUSE-9. MUSE-6 is fully NTSC compatible, and at one time NHK
referred to it as MUSE-4 or MUST-NTSC. MUSE-9 is MUSE-6 with an
additional 3 MHz signal that can be transmitted on an adjacent channel
to add extra motion resolution and reduce artifacts in the MUSE-6
signal. Since the 8.1 MHz bandwidth of the parent MUSE-E signal
exceeds that of the NTSC channel, a change of scanning from 1125- to
750-lines, like Narrow MUSE, is used. On a conventional NTSC
receiver, MUSE-6 shows a 16x9 image centered in the 4x3 frame with 345
active lines. The additional, high resolution, components of the
signal are time compressed and "hidden" in the letterbox bars above
and below the image. In addition to reduced resolution during
movement, images blur due to the four-field sampling and
time-compression of the signal. High resolution is achieved by
spectrum folding (sub-nyquist sampled aliasing). Two subcarriers,
separated by one-half and one-quarter the frame rate, carry high
frequency sidebands that are interleaved in the baseband luminance
from 1.9 to 3.9 MHz. This interleaving is under the control of a
motion detector and is disabled during motion in the image. Total
resolution specs are complex. For static scenes, horizontal luma
resolution extends to 410 lines at 600 vertical lines and up to 500
horizontal lines at 345 lines vertical. During motion, below 345
vertical lines, horizontal luma resolution is 210 lines; below 173
vertical lines, it extends to 410 lines. The I and Q chroma signals
resolution are one-half to one-quarter the luma during still and
motion scenes. Diagonal chroma and luma resolution varies.
At one time, Pioneer was considering releasing MUSE-6 encoded
LaserDiscs in the US. This was possible since they would have played
on conventional equipment. Eyewitness descriptions of the MUSE-6
image are not very complimentary. Considering ClearVision and
ClearVision II are used in Japan instead of MUSE-6, it seems clear
that it didn't perfrom well.
MUSE-9 adds an additional 60 to 100 lines of resolution to the MUSE-6
image. It also permits transmission of image areas in motion.
The MUSE systems are VERY complex. Even a basic MUSE-E satellite
decoder is quite complicated. Still, the system worked and contributed
GREATLY to the store of knowledge in video compression systems;
Predictive coding, motion vectors and compensation... In 1993, NHK
introduced a new, improved, MUSE-E encoder, that eliminated some of
the blurring in moving objects it was fully backwards compatible
with existing MUSE-E decoders - no LaserDisc's were ever made with the
newer "MUSE-2" encoder. One satellite channel is still transmitting
in MUSE Hi-Vision, but Digital Hi-Vision has taken over. It's really
not a big deal since analog MUSE Hi-Vision was a big flop in Japan -
actually, MUSE-to-NTSC was a big success; in the first year of test
broadcasts, over 100,000 MUSE-to-NTSC converters (so-called MN
converters) were bought by the Japanese public.
Ty C. :-)