by groundskeeper willy » Mon Apr 12, 2021 7:20 pm
When PPM was originally rolled out, there were problems with talk stations claiming faulty ratings, and it was due to the technology at the time. For music stations, the PPM watermark signal has plenty of frequencies to be masked with, so the strength of the watermark can be boosted up, which pretty much ensures that the listener's PPM receiver will capture and log the signal.
Talk stations found that they had to keep the watermark signal low, as there was no way to really mask the watermark during silence (ie the normal pauses during conversation). While the watermark is technically inaudible, if the watermark signal was too high, it could create audible artifacting as it was being pushed through the station's processing chain. So talk stations had to find that balance point where they still had PPM encoding but it wasn't compromising the signal heading out the transmitter, and that point was sometimes too low to be captured properly. Hence the P.O.'ed PD's at stations that suffered with flawed ratings during the early days of PPM.
Really isn't much of an issue anymore, thanks to the pointy-headed engineering nerds who've done the math and fine-tuned the encode software that now works like it's suppose to. Sure, there are still occasional problems with ratings 'glitches', but that's usually a result of equipment not being calibrated correctly at station level.