In the context of RF modulators, different audio subcarrier offset frequencies are used for packing a sound signal alongside a video signal for traveling together down a single coaxial antenna wire to an analog TV. These are each technical parameters for their respective CCIR video broadcasting standards. Using the correct frequency is important when using an RF connection between a console and a TV to ensure the sound is decoded and working well.
PAL-B and PAL-G
PAL using system B (VHF) and G (UHF) video uses an audio carrier spacing of 5.5 MHz. This is the standard used in the majority of PAL territories' analog TVs including Australia, most of Western Europe, the Nordic countries, former Yugoslavia, Turkey and the Middle East.
PAL-I
PAL using system I (UHF) video uses an audio carrier spacing of 6.0 MHz. In Europe this standard was only used in Great Britain and Ireland but outside this region was also used for TVs in Hong Kong and South Africa. Most official RFU adapters from Sony, Sega, and Nintendo's 64 have a switch to change between "G" and "I", ensuring audio compatibility for the adapters between both PAL-B/G and PAL-I sets. Switching to the incorrect setting would result in static audio noise.
PAL/SECAM-D and PAL/SECAM-K
PAL using system D (VHF) and K (UHF) video uses an audio carrier spacing of 6.5 MHz. This system was predominantly in use in Eastern Europe where the broadcast system was SECAM (before switching to PAL in the 1990s[1]) including the former USSR, Poland, Czechoslovakia and Hungary, as well as in Mainland China. Video game manufacturers did not create separate RFU adapters for the PAL-D/K audio frequency, instead packing AV cables (e.g. composite RCA) at the retail level to bypass the TV's radio frequency tuner entirely.
SECAM-L
The system L standard using SECAM video and audio was used only in Metropolitan France. Its audio spacing offset is 6.5 MHz but is amplitude modulated (AM) instead of frequency modulated (FM) as the SECAM-D/K. Alongside its video output (positive modulation instead of negative), it is completely incompatible with SECAM-D/K, PAL-B/G and PAL-I analog TVs.
Because of circuit complexity making it difficult to create converters, video game manufacturers designed specific models or configurations for France to bypass RF entirely. French NES models replaced the internal RF modulator with a custom circuit to output through a proprietary Nintendo SCART (Péritel) cable. Later consoles like the Sega Mega Drive and the PlayStation shipped in France exclusively using multi AV to RGB SCART cables.
NTSC-M
A 4.5 MHz sound carrier is used for RF modulators on all NTSC TVs worldwide per the system M standard.
Links
- https://en.wikipedia.org/wiki/PAL
- https://en.wikipedia.org/wiki/SECAM
- https://analogtv.net/controls/audio