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Respect achievable deviation in BS.412 limiter
https://forums.stereotool.com/viewtopic.php?t=4406		 Page 1 of 1
Author:  AlexL [ Sat Dec 15, 2012 2:08 am ]
Post subject:  Respect achievable deviation in BS.412 limiter
Hi,

in our setup, I would need a feature because our FM transmitter has a broken (well, mechanically broken rotary switch) input stage: for the maximum recommend input level, we only get e.g. 55 kHz deviation. I want ST to respect this in the level calculations for the BS.412 limiter. I.e. the user interface would get a checkbox "Clip to max. dev." which is normally enabled and leads to the current behaviour. When it is disabled, ST would not lower the clipping range to the deviation set in this dialog but assume that the output level of the sound card for 0 dBFS matches the deviation set in this dialog. This would equally result in a denser sound with the difference that ST does not need to scale the signal.

I hope that this is clear enough, Hans. Otherwise it would be cool if you could ask.

Kind regards,
Alexander
Author:  Bojcha [ Sat Dec 15, 2012 3:06 am ]
Post subject:  Re: Respect achievable deviation in BS.412 limiter
hi..
First you need to fix that "potentiometer"
Second.. if you use BS.412 then first turn it off, push "advanced clipper" and you should have 75kHz modulation on air. You need some measurement tool to confirm that! (Don't always belive what transmitter meters shows)
Then when you are sure that you have 75kHz modulation / 9% pilot .. you can turn ON BS.412 and always be sure that you are are at good mpx out level.
Afaik, ST will sometimes make peeks to 74-75kHz with BS.412, and it's only available BS.412 processor that can actually go up to 75kHz. Usually other processors are under 65%.
Author:  AlexL [ Sat Dec 15, 2012 11:01 am ]
Post subject:  Re: Respect achievable deviation in BS.412 limiter
Quote:
hi..
First you need to fix that "potentiometer"
Second.. if you use BS.412 then first turn it off, push "advanced clipper" and you should have 75kHz modulation on air. You need some measurement tool to confirm that! (Don't always belive what transmitter meters shows)
Hehe, yeah, we could let it be fixed but that does not really make sense as this transmitter is just being used for a few months (then we plan to buy a new one) and we don't have the expertise to do it on our own. I admit that this feature is only useful to very few users, but its also easily implementable. If it doesn't land, we will just set the max. dBr value to more than 0, that should also work, right? :)
Author:  hvz [ Sat Dec 15, 2012 11:31 am ]
Post subject:  Re: Respect achievable deviation in BS.412 limiter
Actually, it's not very clear to me at all... Unless I misunderstood something, the input level of the transmitter needs to be increased a bit and that's all. Except for that, a signal where the clipping level goes ABOVE 75 kHz will just cause you to get your station taken off the air.. And at the normal settings the peak level where clipping occurs is already equal to the maximum output level of the sound card.

But most importantly: The relation between BS412 level and peak deviaton is fixed. If one is good, the other will automatically also be good. If your peak level is at 55 kHz then your dBr level will also be almost 30% (3 dB) too low.
Author:  AlexL [ Sat Dec 15, 2012 11:34 am ]
Post subject:  Re: Respect achievable deviation in BS.412 limiter
Quote:
Actually, it's not very clear to me at all... Unless I misunderstood something, the input level of the transmitter needs to be increased a bit and that's all. Except for that, a signal where the clipping level goes ABOVE 75 kHz will just cause you to get your station taken off the air.. And at the normal settings the peak level where clipping occurs is already equal to the maximum output level of the sound card.
I do not want to get the station taken down the air and I cannot increase the input level anymore at all. Our transmitter maxes out at ~ 55 kHz.
Quote:
But most importantly: The relation between BS412 level and peak deviaton is fixed. If one is good, the other will automatically also be good. If your peak level is at 55 kHz then your dBr level will also be almost 30% (3 dB) too low.
OK, then I will be able to adjust it using the dBr slider.
Author:  hvz [ Sat Dec 15, 2012 12:08 pm ]
Post subject:  Re: Respect achievable deviation in BS.412 limiter
Yes. Just make sure you really measure the signal strength properly... I heard that the regulators in Germany are VERY strict.
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