Hola Ozzy,
Saludos hermano , I do have more information about the limiters and also a description of the function of an compressor and the AGC/Limiter unit.
Also I was able to locate the manual of the 424-A so you can review the operations a features of the 424-A you can download the manual in Adobe Acrobat format from Orban's website at:
ftp://ftp.orban.com/422A_424A/
The following link has very good references about audio processing, explaining the different uses for the equipments and with schematics:
http://www.261.gr/proradio.html
The next link has very good information about compressors, explaining the different uses for the equipment, and has various compressor products
refrences:
http://www.tweakheadz.com/compressors.htm
http://www.dbxpro.com/162SL.htm
http://www.dbxpro.com/166XL.htm
http://alesis.com/products/3630/
And also I do have here an explination of the functions of the Compressor, AGC and Limiter:
As you know, if you listen to a song or sound source you can note that audio levels change at a fraction of a second, for example a music portion sound is very soft, and suddenly the sound starts to raise, here we do have already a change in sound level or the modulated level changes also.
For example if you are playing a CD you can notice that each track does have some variation in the audio level, in broadcast situation, we would like to broadcast the same quality that we are listing in the studio or control room to the listners at home, but also we would not like to have the listners going each time at the radio to turn up and down the volume control for a music or an other audio source that is being played.
To help the operator to get an consistent audio level being broadcast to the listner, there are solutions for audio processing.
We do have an compressor, which compreses the sound for preventing high peaks, so if you get an high peak of music, the compressor will hold those high peaks, in all compressors you will find the adjustments that let you customize the 'attack point' (to hold the peaks) to your preference.
The AGC (Auto Gain Control) is an automatic leveler, that maintain the audio source at an consistent level all the time, for example if there are low sections in a music, for example a violin, or piano, normally without an AGC, you can barely listnen to them, with the AGC, all these low sections of the music are also being amplified and leveled.
The Limiter is like a 'wall' for the audio, for example you got during a narration or music:, somebody start screaming, the limiter acts as a wall to hold all those screaming to the adjusted limit level, so you won't have overmodulation and distortion.
In an AGC/Limiter unit, at the audio input 'stage', the AGC circuit analyses the amount of audio gain that is 'pushed' into the unit, and from there it will automaticly level the audio gain to maintain the levels equally, and also the case if there is too much audio being 'pushed' into the unit the limiter will activate and act to prevent overmodulation.
In commercial broadcast there is mostly use the AGC/Limiter unit, like Optimod (from the same Orban Corporation) did something particular, they did design the AGC/Limiter and equalizer along with the stereo generator all in one unit, with the result that you got different versions of the Optimod 8000-A, 8100, 8200, and currently 8400.which is widely used in a lot of radio stations.
Here is a link that explains the designs of the Optimods:
http://www.oldradio.com/archives/hardware/ops.htm
http://www.soundprocessing.nl/hisbob.html
In my audio set-up for the Ramsey transmitter, I have done the following set-up for the audio chain:
1. Program Out console ----> Equalizer In ----->
2. Equalizer Out ----> Marti CLA 40 AGC ----->
3. Marti CLA 40 AGC -----> Ramsey X-Mitter. IN
The 'clean' audio comes from the console and is feeded into the 12 band 'Vector Research' equalizer, the equalizer will remove all high frequencies and sillabance that are in a music or speech, and also to shape the audio, with a equalizer you can adjust the sound to your preference, always when adjusting a equalizer, I use an headphone, and after that I judge the sound on the speakers.
After the equalizer the audio is directed to the two Marti AGC/Limiter CLA 40, units,(one unit is for Left, the other unit is for Right) the Marti's acts as an leveler and limiter, if suddenly the music level can become low, the Marti will automaticly level the music back, and if there can be a very high or heavy peak, the Marti will hold these peaks to prevent overmodulation and distorition, and after this the audio is feeded into the Ramsey Transmitter.
In the previous version of Ramsey 1 Watt X-Mitter, the stereo generator chip is very sensitive to high frequecies, so I always adjusted the limiters to 0 db (100%) modulation to prevent distortion, and it worked always very good, with a great sound on the air.
as I understand that the FM 100 B-TX are more tolerant to high frequencies, so you can go more 'louder' within the 0 db range, without distortion.
That is also a advantage of the AGC/Limiter that you can have a 'loud' sound and at the same time staying in the 0 db (100 % Modulation) range
Bueno hermano, para cualquier detalle addicional como tambien si desea mas informacion, me puede escribir libremente.
Saludos,
Richinald.
