Analog mono
Analog mono is a single-channel audio signal format used in television and video equipment from the earliest days of broadcast television through the late 1980s, when stereo broadcasting became widespread. Monaural audio was the universal standard for television sound for over three decades, and the vast majority of CRT televisions manufactured before the mid-1980s support only mono audio.
History
Television audio was monaural from the inception of commercial broadcasting in the late 1930s. The audio signal was transmitted alongside the video carrier using frequency modulation (FM) on a subcarrier 4.5 MHz above the video carrier in the NTSC system, or at 5.5–6.5 MHz depending on the PAL/SECAM variant. This mono FM audio remained the sole broadcast television sound format in the United States until the FCC adopted the Multichannel Television Sound (MTS/BTSC) stereo standard on 23 April 1984, and in the United Kingdom until NICAM digital stereo broadcasts began on BBC2 in July 1986.
Even after stereo broadcasting was introduced, all stereo systems maintained full backward compatibility with mono receivers. The BTSC system transmitted the stereo sum (L+R) as the main audio channel, so existing mono televisions continued to receive a perfectly usable mixed-down signal. Similarly, NICAM broadcasts retained the legacy FM mono carrier alongside the digital stereo subcarrier. This ensured that mono CRT televisions remained functional throughout the analog broadcast era.
Signal Characteristics
| Parameter | Value |
|---|---|
| Channels | 1 (monaural) |
| Signal level | Approximately 1V peak-to-peak (line level) |
| Impedance | 10 kΩ typical (high-impedance input) |
| Frequency response | 50 Hz – 15 kHz (broadcast); wider for direct line-level connections |
| Common connectors | RCA (single white or black jack), SCART (pin 3 output, pin 6 input), 3.5 mm TS jack |
Mono audio connections use a single unbalanced cable, typically terminated with an RCA connector color-coded white (or sometimes black) on consumer equipment. In European equipment with SCART connections, the mono audio signal is carried on the left channel pins, with many televisions internally bridging both speaker channels from the single input. Some portable and budget CRT televisions used a 3.5 mm mono jack for audio input or headphone output.
Use on CRT Equipment
Virtually all CRT televisions manufactured before 1985 are mono-only, with a single internal speaker. Budget and small-screen CRT sets continued to ship with mono audio well into the 2000s, as stereo decoding added cost that was unnecessary for sets with small, closely spaced speakers. Mono audio was also common on:
- Professional monitors — most Sony PVM and BVM broadcast monitors output mono audio, as audio quality was not their primary concern. Some models provide a single internal speaker for confidence monitoring.
- Portable CRT televisions — nearly all battery-powered portable sets from manufacturers like Sony, Panasonic, and Casio used mono audio to conserve power and reduce size.
- Security and medical monitors — specialized CRT displays in these fields typically offered mono audio at most, if any audio capability was included.
For retro gaming, the mono audio output of many older consoles (Atari 2600, NES, Sega Master System) was well-matched to mono CRT televisions. These consoles output a single audio channel through the RF modulator or a single RCA jack. Later consoles that output stereo could be connected to a mono television's single audio input without issue, though the left and right channels would need to be combined using a Y-adapter or by connecting only one channel.
See Also
- Analog stereo — Two-channel audio format
- Composite (CVBS) — Video signal commonly paired with mono or stereo audio
- RF — Combined audio/video signal carrying mono or stereo sound
