Once you listen to any Czech FM broadcast channel, you can always recognize their modulation. Why? Czech Republic performs the loudest audio processing in this part of Europe. However, each FM broadcast in this country must comply the ITU-R BS.412-9 recommendation till the end of this year, including both public and commercial programs. What does it mean? The average deviation will be greatly decreased.
Some stations are already broadcasting using new standard, some not. There is a short comparison of ČRo 1: 88.5 Trutnov (regular modulation) vs. 95.9 Liberec (limited in compliance to the BS.412-9). This video contains also an announcement during Radiožurnál news in Czech language about the upcoming changes:
Detailed technical information is provided in the Recommendation ITU-R BS.412-9:
For the radio-frequency protection ratios given in Fig. 1 and Table 3, it is assumed that the maximum peak deviation of ± 75 kHz is not exceeded. Moreover, it is assumed that the power of the complete multiplex signal (including pilot-tone and additional signals) integrated over any interval of 60 s is not higher than the power of a multiplex signal containing a single sinusoidal tone which causes a peak deviation of ± 19 kHz.
It is important that the limits for modulation levels given above should not be exceeded, otherwise the radiated power of the transmitter has to be reduced in accordance with the increased figures for protection ratios given in Annex 2.
NOTE – The power of a sinusoidal tone causing a peak deviation of ±19 kHz is equal to the power of the coloured noise modulation signal according to Recommendation ITU-R BS.641, i.e. a coloured noise signal causing a quasi-peak deviation of ±32 kHz.
The current deviation limit (75 kHz) will remain unchanged, but the average deviation will be greatly decreased. This may mean better, not so over-compressed sound and a main benefit for DX-ers – good reception with narrower IF filters.
Note that stereo pilot has typically 6 ~ 7.5 kHz injection level and the RDS subcarrier (2 ~ 4kHz level) also counts in. New ITU limits will also improve reception in hilly terrain, as the multipath distortion will be less audible. Don’t forget about adjacent channel interference, especially using tuners with the adaptive filter bandwidth feature, like Sony XDR-F1HD, which will provide much better audio next to another signal.