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 Post subject: 75Khz Limiter
PostPosted: Sun Mar 29, 2009 1:18 pm 

Joined: Tue Jul 22, 2008 2:21 pm
Posts: 14
Hello !

Is possible with Stereotool to keep audio in the 75khz bandwith ?
What is simple way to limiting this ?
(i have problem with inspections in my radio station).

Thanks !!


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 Post subject: Re: 75Khz Limiter
PostPosted: Sun Mar 29, 2009 1:52 pm 
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Joined: Mon Mar 17, 2008 1:40 am
Posts: 9523
Hello Iggy,

First of all, I recently found a a bug in version 3.40 than can cause small peaks... So download the new beta (should be released as 3.50 in a few days):

Winamp DSP plugin: http://www.stereotool.com/download/dsp_ ... r_BETA.exe
Stand alone version: http://www.stereotool.com/download/ster ... r_BETA.exe
Command line: http://www.stereotool.com/download/ster ... r_BETA.exe
VST version: http://www.stereotool.com/download/vst_ ... l_BETA.dll

Make sure that:
- HARD LIMIT is enabled
- FM transmitter page: Set "Keep composite MPX signal within limits" to "Yes, always" (the default is "depending on main quality setting", if the quality is Normal or High it should already be ok).

These two steps will keep the signal that is sent TO THE SOUND CARD tightly limited.

However... There are still a few things that can cause the signal to peak outside the 75 kHz bandwidth:
- If the signal strength to the transmitter is too high.
- If the sound card CHANGES the signal in any way.
- If the CABLE between the sound card and the transmitter changes the signal in any way (and I've measured and even heard differences between using a 5 m and a 10 m cable, so this is very likely to occur unless you are using a very short very high quality cable).
- If the transmitter itself does something to the signal.

Sound card and cable issues can probably be solved using the "FM transmitter calibration". But you probably need some equipment to measure the transmitted signal. Most devices that do this are very expensive. I've heard about the Pira FM Broadcast Analyzer ( http://pira.cz/fm_broadcast_analyzer/ ), but I don't know how good it is.

If this doesn't help enough and occasional peaks are still present, you could consider putting a simple composite clipper just in front of the transmitter. That way, any peaks that are still present due to calibration, cable and sound card differences will be removed before the signal is actually transmitted. This will cause artifacts in the sound, but if everything is configured correctly, it SHOULD not occur.


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 Post subject: Re: 75Khz Limiter
PostPosted: Tue Jun 21, 2011 1:36 am 

Joined: Fri May 13, 2011 11:21 pm
Posts: 52
Just to add some info..
From my experience after testing it with Pira75, YES the modulation can be maintained really tight to 75KHz. But, keep in mind, that a small clipper just in front if the transmitter will always keep the mod into legal limits.


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