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.