Those answers from WDCX and Rich match the reality one would reasonably expect from the local marketplace... based on each station having a different set of people making decisions.
Of course now many stations are group owned and might have the same few people deciding how things function, but we would need inside knowledge to know that.
The best judgement we can make is whether a station sounds "good" or "not", based on our subjective judgement, and limited by the particular receiver we use.
When I return, in one minute, the results of my Stereo Tool experience.
I noticed that Hans Van Zutphen, author of the Stereo Tool audio processing software, now calls his product "Stereo Tool." Previously I think it was called "Stereotools."
As first reported on this site by John WDCX, Stereo Tool V 7.50 is capable of setup for 125% asymetric modulation of an AM transmitter. This is true, and it's an amazing feature that can do away with the expense and rack bloat of clunky processing gear.
But certain things must be kept in mind when setting up.
Since this audio chain also drives three internet streams they cannot be driven at 125% asymetric.
Since the audio chain passes through a STL (Studio Transmitter Link), basically an FM transmitter/receiver combination, that system must be held at no more than 100% modulation.
Since my internet streams are stereo, the "forced mono" that is part of the AM Transmitter Setting in Stereo Tool must be defeated.
Since the NRSC Preemphasis is jumpered in my AMT5000 transmitter it cannot also be set to NRSC within Stereo Tool, nor would NRSC be wanted for streaming audio.
But guess what? Taking all of these factors into account, it is possible to fine tune Stereo Tool and get it to serve all these needs.
The adjustment for asymetrical processing is buried from Stereo Tool:
"Ugh. I see that they are hidden when the GUI is in Basic mode. Oops.... Go to Configuration and set "Operating mode" to at least Advanced.
Edit: Fixed for the next version."
That's right, John WDCX, the Advanced Operating Mode must be chosen to get into the AM Special Section in the DSP Stereo Tool version.
Stereo Tool is a massive, highly complex, extremely professional work of engineering art.
Hans Van Zutphen, the author, is a great genius.
Yes he is.
Putting on my "commercial radio engineer" hat for a moment, as others have said, there is no answer. Every station has their own ideas, their own equipment, and their own desired outcome.
In response to a question/comment above, there IS a limit for high power, commercial FM stations, the same limit for a lower power FM station. You can't modeulate more than 100%. That's it. There's a smidgeon of leeway if you are running something on a subcarrier, e.g. if you've got an RDS unit running and you're injecting, say 6% modulation you are then allowed to modulate your main signal over 100% by 50% of that RDS injection, so you could get away with modulating peaks fo 103%.
The amount of compression does not have any effect on maximum modulation allowed. You can compress a little or a lot and still modulate 100%. It's just that with a crapload (a technical engineering measurement) of compression you'll notice the needle on the modulation meter barely ever fluctuates from the 100% line. This makes for a loud station and a lot of listener fatigue.
The station I engineer is a 100,000 watt station, and we share the building with a 100,000 watt public station -- in fact they own the tower and building, we've leased tower space and room for our transmitting equipment in the building for decades. I've now done the engineering for three different owners (I've outlived two of them). The first believed in good sound, less processing, and a very clean, nice sound. We had very basic CRL processing that mostly prepared sound for air, and prevented overmodulating. The second owner wanted us louder, so I tweaked things to bring it up a bit, but still using the old gear and minimum compression. The current owner wants to be as LOUD as the other stations, or LOUDER, so he bought a new Optimod from Orban, and now we're pumping it out pretty good and the modulation meter pretty much stays between 95 and 102% all the time (we have an RDS injecting at 6% so we can legally be 103% but I prefer a tad of leeway).
So, the answer is, there is no answer. This new processor actually lets you set up different settings for different programming. It can do it by time, or by remote control. e.g. a sports broadcast comes on, the operator can hit a button and change the processing for settings optimized for sports, or for a talk show, or for a rock and roll show, etc.
I wold be surprised if a large FM was purposely overmodulating and causing interference. First, they're not going to do with with use of too much compression, they would do it by simply overmodulating the transmitter. Note that FM doesn't gain more signal output or coverage with more modulation as AM does, it just takes up a bit more bandwidth. In a major market with strong competition, a station overmodulating would be quickly called out by competitors. Not to mention not passing an inspection. And it's quite easy to check FM modulation in the field. There are probably other causes for interference, but overuse of compression isn't going to be it. I can't remember the last time I saw a violation for a commercial FM for overmodulating. There is no limit to use of compression other than how much lack of dynamic range a listener can take.
Tim in Bovey
Tim in Bovey
Thanks Tim for the more detailed reply. I am in total agreement with you. I simply kept it simple by stating and maybe confusing others, that every station has its own personality with regard to processing.