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PostPosted: Fri Mar 05, 2010 9:37 pm 
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Joined: Tue Dec 08, 2009 12:49 pm
Posts: 47
Location: Den Haag, The Netherlands
Does pre-emphasis within stereo tool also affect the stereo signal? Or is it done before stereo encoding?

The reason why I ask this, is because when I calibrate my transmitter, I check every frequency range and set it as high as possible without getting distortion (I have no good measure equipment to do it any other way, but it works good for me). However, the 23 - 53 khz sliders, I can set them much higher than the 10240 Hz slider without getting distortion, which surprised me.


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PostPosted: Wed Mar 10, 2010 1:31 pm 
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Joined: Tue Dec 08, 2009 12:49 pm
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Location: Den Haag, The Netherlands
Nevermind, I always thought pre-emphasis was there to reduce noise in higher frequency regions in the fm signal, but reading about it, it seems to reduce 'audible' noise instead. So I thought the fm signal had to be pre-emphasised, but it's just the audio, right?


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PostPosted: Fri Mar 12, 2010 2:31 am 
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Hi Kakoon,

If that's how you configure the sound I hope you reduce the volume afterwards, otherwise many people will get distortion (radios differ!)

You're right, the pre-emphasis is done on the audio before stereo encoding occurs. (If not, the stereo signal would have to be so extremely loud that the entire volume would need to be dropped to an insanely low level).


About not having measuring equipment: What I did (and I really don't know anything about hardware at all): I opened up my old FM receiver, and just started typing chip names (which are printed either on the chip or on the print) in Google until I found one that was an MPX decoder. Then I just soldiered a wire from the input (also found that online) of that chip and connected it to my ESI Juli@ sound card input (192 kHz capable).

Important: If you do this, make sure to keep the cable as short as possible, as even short cables lead to signal loss at higher frequencies. Oh, and before connecting it to your relatively expensive sound card: First connect it to something that may be damaged. Just in case you chose the wrong pin on the chip and have a 12 V line or something annoying like that.


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