Analog stereo

Analog stereo is a two-channel (left and right) audio signal format and the most common audio output found on consumer CRT televisions from the mid-1980s onward. The introduction of stereo television broadcasting transformed the home viewing experience and drove the development of CRT sets with improved speaker systems, stereo amplifiers, and dedicated audio output jacks for connection to external hi-fi equipment.

History

North America — MTS/BTSC

Stereo television sound in North America was enabled by the Multichannel Television Sound (MTS) standard, developed by the Broadcast Television Systems Committee (BTSC) and adopted by the FCC on 23 April 1984. The system encoded stereo difference information (L−R) onto a 31.468 kHz double-sideband suppressed carrier alongside the existing mono-compatible sum signal (L+R), using dbx companding for noise reduction.

NBC began sporadic stereo transmissions on 26 July 1984 with The Tonight Show Starring Johnny Carson, though initially only its New York flagship station WNBC was equipped. ABC and CBS followed in 1986 and 1987 respectively, and by late 1994 all four major networks had their entire prime-time schedules in stereo. One of the first consumer receivers with BTSC decoding capability was the RCA Dimensia system, released in 1984.

The MTS standard also included a Second Audio Program (SAP) channel, often used for Spanish-language audio tracks or video description services, and a PRO channel reserved for broadcaster use.

Europe and Asia-Pacific — NICAM and Zweikanalton

Two competing analog stereo television standards emerged in the PAL/SECAM world:

NICAM (Near Instantaneous Companded Audio Multiplex) was a digital stereo system developed by BBC Research in the 1970s, originally for studio-to-studio audio links. The public broadcast variant, NICAM 728, transmitted 14-bit PCM audio (companded to 10 bits) at 32 kHz sampling rate over a 728 kbit/s DQPSK-modulated subcarrier. The first public NICAM broadcast was the opening night of the BBC Proms on BBC2 on 18 July 1986. NICAM was adopted across the United Kingdom, France, Spain, Scandinavia, China, Hong Kong, Australia, and New Zealand, among over 50 countries by the mid-1990s.

Zweikanalton (A2 Stereo) was an all-analog system developed by Germany's Institut für Rundfunktechnik (IRT), first introduced on ZDF on 13 September 1981 — making West Germany the first European country with multiplexed television stereo. It used a second FM carrier 242 kHz above the primary sound carrier. Zweikanalton was adopted in Germany, Austria, Australia, the Netherlands, and several other countries. Its lower implementation cost made receivers cheaper than NICAM-equipped sets, though audio quality was somewhat lower.

Both systems maintained backward compatibility with existing mono receivers and supported bilingual audio modes.

Signal Characteristics

Parameter	Value
Channels	2 (left and right)
Signal level	Approximately 0.5–2V RMS (line level, varies by equipment)
Impedance	10 kΩ typical (high-impedance input); 47 kΩ on some hi-fi equipment
Frequency response	50 Hz – 15 kHz (broadcast); 20 Hz – 20 kHz (direct line-level)
Common connectors	RCA pair (red = right, white = left), SCART (pins 1–6), 3.5 mm TRS stereo jack

Consumer stereo audio connections use a pair of unbalanced RCA cables, universally color-coded red for the right channel and white (or sometimes black) for the left channel. European equipment commonly carried stereo audio bidirectionally through SCART connectors (pins 1/2 for right channel in/out, pins 3/6 for left channel in/out, pin 4 for audio ground). Many CRT televisions also provided a 3.5 mm TRS stereo headphone output, and some included a 3.5 mm stereo audio input.

Use on CRT Equipment

Consumer televisions

Stereo-capable CRT televisions became mainstream in the mid-to-late 1980s, initially as a premium feature on larger sets. By the early 1990s, stereo audio with built-in speakers was standard on mid-range and larger consumer CRTs from all major manufacturers. Key developments included:

Dedicated stereo speaker systems with separated left/right drivers, sometimes in detachable speaker wings
"Virtual surround" processing (e.g., SRS TruSurround) on late-model consumer CRTs
Audio output jacks (RCA pair or headphone) for connection to external amplifiers and home theater receivers
SAP/MTS selector buttons on North American remotes for accessing alternate audio tracks
NICAM indicator lights on European and Asia-Pacific CRT televisions

Professional equipment

Professional CRT monitors generally prioritized video quality over audio, but many included basic stereo monitoring capability. Sony PVM models with stereo audio typically provided a pair of BNC or RCA audio inputs alongside video connections. Higher-end broadcast monitors sometimes included balanced audio inputs on XLR connectors.

Retro gaming

Stereo audio became relevant for gaming with the arrival of consoles that output two-channel sound, including the Super Nintendo (1990/1991), Sega Genesis/Mega Drive (via headphone jack), and subsequent generations. Connecting a stereo console to a stereo CRT via RCA cables provides the intended audio experience — particularly important for games with spatial audio cues or high-quality soundtracks. Some enthusiasts route console stereo audio to external speakers or amplifiers while using the CRT purely for video, which can provide a significant upgrade over the typically modest built-in speakers of consumer CRT televisions.

References