Editing Radio Data System (section)

==RDS compatibility==
The RDS sub-carrier at 57&nbsp;kHz occupies ±2&nbsp;kHz of the composite spectrum which in theory keeps it above the upper cutoff of the stereo subcarrier at 53&nbsp;kHz. However the 53&nbsp;kHz cutoff is entirely dependent on the performance of the 15&nbsp;kHz low pass filters used before the stereo encoder. In older equipment, these filters were only designed to protect the 19&nbsp;kHz pilot and sometimes did not provide sufficient protection to the RDS subcarrier when a significant amount of stereo information was present. In this situation, stereo enhancement devices combined with aggressive audio processing could render the RDS subcarrier unreceivable.  In some modern audio processors the 15&nbsp;kHz low pass filters have a 16.5&nbsp;kHz cutoff.  This can also degrade the reception of RDS.

Composite clipping systems may also degrade the RDS sub-carrier because of the harmonics created by the clipping. More modern composite clippers include filtering to protect the RDS subcarrier.

The RDS subcarrier typically uses 2–4&nbsp;kHz of carrier deviation. Therefore, the deviation available for the program material is reduced by this amount, assuming the usual 75&nbsp;kHz deviation limit is not exceeded.