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 Post subject: Audio Routing
PostPosted: Tue Jul 18, 2017 8:35 pm 

Joined: Mon Feb 24, 2014 7:31 pm
Posts: 41
Hi Hans!
It would be a good idea to implement an "Audio Routing", especially for the FM Output. The purpose is to select the sound channel to send the signal MPX, RDS signal, SCA.


Without "Audio Routing", everything is sent through both channels:

* Left Channel -> MPX+RDS+SCA
* Right Channel -> MPX+RDS+SCA


With "Audio Routing", each signal could be sent on a separate channel at the same time:

* Left Channel -> MPX
* Right Channel -> RDS
or
* Left Channel -> MPX+RDS
* Right Channel -> SCA
or
* Left Channel -> 19 kHz
* Right Channel -> MPX+RDS

Best regards from Chile
PD: Sorry for my bad english :(


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 Post subject: Re: Audio Routing
PostPosted: Sat Aug 25, 2018 5:29 am 

Joined: Sat Aug 25, 2018 5:26 am
Posts: 3
Made an account to say this would be awesome.

I have trouble with just using MPX. It seems to cut out a good portion of the mono signal, which significantly lowers the bass response. It would be nice to have stereo/RDS on one channel with the mono on another so I could use the line in port for mono.


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 Post subject: Re: Audio Routing
PostPosted: Sat Aug 25, 2018 7:59 pm 
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Joined: Tue Mar 17, 2009 2:56 pm
Posts: 3304
I am strugling to understed how is that usefull (?)

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 Post subject: Re: Audio Routing
PostPosted: Sun Aug 26, 2018 12:48 am 

Joined: Sat Aug 25, 2018 5:26 am
Posts: 3
I've noticed on the CZE transmitters the MPX port has trouble with the lower mono audio frequencies while accepting the higher stereo pilot, stereo signal, and RDS signal, causing a massive loss of bass. I can get it fixed mostly by using one of the line in inputs, but it doubles the mono signal, meaning the modulation has to be lowered, cutting the stereo and RDS signals. I can get it mostly fixed using the soundcard calibration settings, but the setup would be much simpler if I could feed the line in just the mono signal send the stereo pilot and up to the MPX port.


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 Post subject: Re: Audio Routing
PostPosted: Sun Aug 26, 2018 2:05 am 
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Joined: Tue Mar 17, 2009 2:56 pm
Posts: 3304
What you are talking about is pure transmitter problem. You just need clean MPX input. That transmitter probably does not have it and you just need to make one.
Even if you think you can fix problem it that way whole point of clipping/composite clipping is lost.

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 Post subject: Re: Audio Routing
PostPosted: Sun Aug 26, 2018 7:50 pm 

Joined: Sat Aug 25, 2018 5:26 am
Posts: 3
Quote:
What you are talking about is pure transmitter problem. You just need clean MPX input. That transmitter probably does not have it and you just need to make one.
Even if you think you can fix problem it that way whole point of clipping/composite clipping is lost.
The transmitter uses a BNC port for the MPX input
Image

It seems that the port is made for RDS, SCA and other higher frequency signals, not necessarily for the mono audio signals.

The MPX signal is shown here, you can see that from 0-~1000Hz, the signal is severely attenuated.
Image

Compared to other stations, these frequencies are much higher:
Image

Here is the circuit, and it would seem this is all done by design:
Image

The capacitors there would seem to be the cause of the low frequency attenuation as they are not present on the line in path. Now I have no issue desoldering these capacitors and running a jumper there, but seeing as how this is the way the transmitter was designed (and not knowing if this would cause RFI to be allowed in), and seeing as how this is a piece of software designed to modulate transmitters, I would venture to guess it would be more proper to allow the software to run different configurations. Ultimately I can understand how most people would not use a feature like this, but I could still see it coming in handy if someone wanted to use the same soundcard to modulate the same station, both AM and FM for example.


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 Post subject: Re: Audio Routing
PostPosted: Tue Aug 28, 2018 4:34 am 

Joined: Mon Feb 24, 2014 7:31 pm
Posts: 41
Quote:
I am strugling to understed how is that usefull (?)
It would be useful to insert an MPX signal (Without RDS) into the MPX input of the STL and the separated RDS signal into another RDS / SCA input of the STL. On the TX site, the MPX signal can be distributed to other sites without the RDS information. In this way, the local RDS information remains in the original place and the only thing that is massified is the MPX signal.


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 Post subject: Re: Audio Routing
PostPosted: Wed Aug 29, 2018 12:10 am 
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Joined: Tue Mar 17, 2009 2:56 pm
Posts: 3304
Ok that's fine, but what i know L/R is usually distributed nowdays. Wich is also more logical and easier to use.

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 Post subject: Re: Audio Routing
PostPosted: Thu Aug 30, 2018 9:28 pm 

Joined: Mon Feb 24, 2014 7:31 pm
Posts: 41
Yes, but from the ST output, both channels carry the same information. It could be much more useful to distribute the signals to send them in a different channel.


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 Post subject: Re: Audio Routing
PostPosted: Thu Aug 30, 2018 10:32 pm 
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Joined: Tue Mar 17, 2009 2:56 pm
Posts: 3304
Don't get me wrong, if Hans wants to add that routing it's fine with me.

However, whole inustry is based on clean MPX signal, wich nowdays, as we can see, makes some very good benefits. Clippers and composite clippers, and embedded sca's is very good reason to use MPX output from ST, or other processor with similar possibilities. The way you want to route things, this all stuff is not possible.

I would rather look at that transmitter, and find/make clean MPX input. That's just me.

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