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PostPosted: Tue Jun 03, 2014 1:02 am 
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Location: Yakima, Washington
AM Stereo seemed like an interesting idea, and it took me some time to go over schematics and books to see how GNURadio would do it.

The graph, along with Stereo Tool's processing, produces a wonderful C-QUAM/NRSC complaint signal. The generated signal has been tested with both software and hardware receivers. You can get the flowgraph and ST preset on the gr-cquam github.

Here are some (old) samples:

NORMAL AM RADIO (5KHz AF | Mono)

AM C-QUAM (11KHZ AF| Stereo)


Last edited by jwjstudios on Sun Jul 27, 2014 10:18 pm, edited 3 times in total.

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PostPosted: Tue Jun 03, 2014 2:41 pm 
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Just a small warning: The clipper in Stereo Tool is not (yet?) C-QUAM compliant. It shouldn't be too difficult to make it compliant though.

Processing L+R and L-R (where apparently L-R shouldn't have asymmetrical processing???) is easy enough, but L and R themselves also need to be protected to avoid distortion in a receiver in some situations, which makes things a bit more difficult.


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PostPosted: Tue Jun 03, 2014 11:45 pm 
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Quote:
Just a small warning: The clipper in Stereo Tool is not (yet?) C-QUAM compliant. It shouldn't be too difficult to make it compliant though.

Processing L+R and L-R (where apparently L-R shouldn't have asymmetrical processing???) is easy enough, but L and R themselves also need to be protected to avoid distortion in a receiver in some situations, which makes things a bit more difficult.
Breakaway is, though I'm not exactly sure how. Haven't looked into AMAX standards yet. It sounds fine enough for now as you can hear in the samples. I at least have an AM-friendly HPF setting, as well as asymmetrical clipping. Natural Dynamics helps a ton too. Though, I'm somewhat bummed to not be able to use pre-emphasis. Can it be done somehow?


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PostPosted: Wed Jun 04, 2014 11:33 am 
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Pre-emphasis is added in version 7.43, which you can download in the News section of this forum!


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PostPosted: Thu Jun 05, 2014 12:34 am 
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Any ETA on the linux port? I sadly can't use the Windows version. Excited to see what it sounds like with AM pre-emphasis. Just using my normal FM limiting settings with AM additions is beyond impressive. Getting the highs back in will make it even better. If you need someone to test it, I have light work this week so have more than enough time to commit to it. :)

Trying to apply pre-emphasis curves in gnuradio is a pain.


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PostPosted: Thu Jun 05, 2014 4:03 pm 
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For now, enable FM and FM 75 us pre-emphasis (but disable all other FM features). This works in version 7.42. It will give you slightly too much pre-emphasis (because the highest freqs need to be reduced a bit again), but it gets pretty close.


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PostPosted: Sun Jul 27, 2014 10:15 pm 
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The CQUAM graph and Stereo Tool preset used are now hosted on github.


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