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| Pre Emph on transmitter cancelling my Stereo coding? https://forums.stereotool.com/viewtopic.php?t=412 |
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| Author: | depach [ Sun Jan 11, 2009 2:44 pm ] |
| Post subject: | Pre Emph on transmitter cancelling my Stereo coding? |
Heya This isnt really anything to do with stereo tool itself, i had this problem before i used stereo tool We bought a new transmitter last year, manufactured by tugicom To this day we have not received a manual for the thing! crazy i know! I now suspect that the pre emphasis on the transmitter is filtering out some of the stereo signal, as the RDS and actual stereo signal gets through to the receiver but the actual sound is def not stereo Our current setup is as follows: Main studio Desk | Stereo Tool (all fm features disabled - purely sound processing as i dont have a 192khz sound card yet) | STL link with stereo encoder and RDS is injected here. RDS uses a sample from the stl links pilot tone to sync with this tone | Z Z Z | STL Receiver, output BNC MPX (DE emph) | Transmitter RCA L set to mono operation as to not filter out the mpx signal Could the pre emphasis on the transmitter be messing with the stereo image? If i feed a sound that goes into one speaker only , the volume on both speakers just goes lower, |
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| Author: | hvz [ Sun Jan 11, 2009 5:13 pm ] |
| Post subject: | Re: Pre Emph on transmitter cancelling my Stereo coding? |
This makes (some) sense: Pre-emphasis is changing the characteristics of the sound. At 15 kHz, the volume is multiplied with a factor 4 or so. Now there are a few possibilities. Pre-emphasis amplifies high frequencies. The stereo pilot tone is at 19 kHz, stereo signal is between 23 and 53 kHz, RDS signal is at 55-59 kHz. If a simple hardware pre-emphasis filter is used, the signals about 15 kHz would be getting louder and louder and at 55 kHz they would be extremely loud. Any hiss in the signal would then also be amplified a lot. So most likely, the pre-emphasis in the transmitter will also contain a filter that filters out (most of) the signal above 15 kHz. Since this is a hardware filter, it will probably not be perfect - which might explain why the receiver is still receiving the 19 kHz stereo pilot tone and some RDS signal. To solve this, you should always perform the pre-emphasis BEFORE adding the stereo and RDS signals. |
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| Author: | depach [ Sun Jan 11, 2009 5:34 pm ] |
| Post subject: | Re: Pre Emph on transmitter cancelling my Stereo coding? |
Thanks! starting to make sense you are really clued up with this stuff  The trick now is to find out how to disable pre emph on the transmitter, without a manual this should be fun, On the exciter board http://www.tugicom.com/Products/images/TX180_LCD.gif there is a 3 pin jumper, 50 or 75 us. They say that can do none so maybe when nothing is closed on the jumper its disabled... |
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| Author: | depach [ Thu Apr 02, 2009 6:50 pm ] |
| Post subject: | Re: Pre Emph on transmitter cancelling my Stereo coding? |
Just an update... We totally bypassed the stereo encoder board on our transmitter (Required some scary soldering hehe) and mounted a bnc mpx input on the box and we are now using only stereo tool for our encoding, stereo and rds Had some great responses but as o posed somewhere else i will have to improve the quality of our mp3's before i can push the settings that i want (mostly stereo depth etc) |
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| Author: | hvz [ Fri Apr 03, 2009 2:07 am ] |
| Post subject: | Re: Pre Emph on transmitter cancelling my Stereo coding? |
Depach, w.r.t. stereo depth, please try the new version (3.51 - yes now already...) - I have changed the stereo phase widener a bit. It should have far less problems with MP3 files now, although it will also sound a bit less wide. (But because of the greatly reduced MP3 problems, you can increase the phase slider a bit further to compensate for that - the result should be better than before). |
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| Author: | depach [ Fri Apr 03, 2009 9:43 am ] |
| Post subject: | Re: Pre Emph on transmitter cancelling my Stereo coding? |
great thx! will load the latest today
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| Author: | depach [ Fri Apr 03, 2009 11:00 am ] |
| Post subject: | Re: Pre Emph on transmitter cancelling my Stereo coding? |
Heya Just noticed your post about the new version and something about RDS bug? I am still on 3.40 should i stay on that version as my RDS is ok as far as i can tell, and i dont want to break it  Jared |
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| Author: | hvz [ Fri Apr 03, 2009 12:54 pm ] |
| Post subject: | Re: Pre Emph on transmitter cancelling my Stereo coding? |
The same bug was also present in all the older versions... So you can just upgrade. It's not a big issue, the only thing is that the RDS signal is causing some "noise" throughout the entire spectrum. After fixing that it will look cleaner, but it's not very likely that you'll notice any difference if you don't attach measuring equipment to it. |
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| Author: | depach [ Fri Apr 03, 2009 12:57 pm ] |
| Post subject: | Re: Pre Emph on transmitter cancelling my Stereo coding? |
great thanks! |
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