Get CD-quality sound with your own TV

Get CD-quality sound with your own TV

L. Gatot S., Contributor, Jakarta

At present, Indonesian television viewers have one state-owned
station and 10 private stations to choose from, following the
launch of several private TV stations early last year.

Most of these stations use stereo sound in their broadcasting
systems. In the past, most TV stations were still using mono
sound, and this change in technology has also led to changes in
the manufacturing of TV sets.

That is why some of the more recent TV models are equipped
with AV stereo speakers and an AV stereo terminal to tune in to
the new technology. But remember, an AV stereo terminal can't
reproduce the stereo sound format from a stereo broadcasting TV
station. To reproduce stereo sound, we need a stereo decoder such
as Nicam and Zweiton.

Zweiton vs Nicam: Zweiton and Nicam are also digital stereo
sound transmission systems for television broadcasts. Zweiton, or
the "A2" system, was invented by German broadcasters back in
about 1975, who have been using it ever since. Zweiton is a
technique for using stereo or dual-mono audio for NTSC and PAL
video.

One FM subcarrier transmits an L+R signal and a second FM
subcarrier transmits an R signal (for stereo) or a second L+R
signal. Although the process is digital, it is a mono analog
audio system that has two different channels (right and left
channels), but its audio characteristics are better than a
standard mono soundtrack.

Usually, our TVs can automatically tell the difference between
a stereo and a "Zweiton" transmission. Nicam (or to give it its
full name, NICAM 728, because the bit rate for Nicam is 728 kbps)
stands for "Near Instantaneous Compounded Audio Multiplex". It is
a technique for implementing digital stereo audio for PAL video
using another audio subcarrier.

The words "Near Instantaneous Compounded" mean only that a
short audio delay is added (a few milliseconds), which is a big
advantage over other digital audio systems when used for amateur
TV. And the term "Audio Multiplex" implies that the system is not
limited just to stereo operation. Nicam was invented during the
early 1980s by the BBC Research Center and Kingswood Warren. It
was first applied to the British "System I" 625 line PAL color TV
broadcasting system.

According to Imam Wahjono, TransTV RF transmission staff
member, Nicam has a right-left frequency and a pilot frequency.
This pilot frequency is read by a receiver, and if we have a
receiver equipped with a decoder for Nicam, we can enjoy the
Nicam audio. But if we don't have a decoder in our receiver, the
receiver cannot receive the pilot frequency, meaning the receiver
cannot process Nicam.

If this is the case, the receiver will only receive mono
audio. Although it is stereo, the quality is still analog.
Theoretically, a NICAM-equipped TV service can offer three-
language support: the FM sound plus NICAM (in twin-mono mode) all
carrying different services.

NICAM is certainly not the first stereo/twin-mono sound system
to be used in Europe, and it currently offers the following
possibilities, auto-selected by the inclusion of a three-bit type
field in the data-stream:

- One digital stereo sound channel

- Two completely different digital mono sound channels

- One digital mono sound channel and a 352Kbit/sec data channel

- One 704Kbit/sec data channel.

What is the difference in the sound quality of these formats?
The "A2" system suffers to some extent from multipath distortion
effects. It has a rather poor signal-to-noise ratio, plus all the
usual troubles with achieving decent linearity with FM modulators
and demodulators.

It also exhibits poor utilization of bandwidth by modern
standards. NICAM offers a totally different approach, providing a
completely new all-digital stereo/twin-mono service in addition
to the one provided by the existing FM sound. NICAM 728 also can
be used to transmit non-audio digital data, so don't be surprised
if you hear CD-quality sound coming from your TV. Nicam is an
incredible digital stereo sound format being used by TV stations
such as RCTI and TransTV. It is near CD quality.