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Old 29-07-2018, 19:40   #1
PhilipOneL
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Join Date: Oct 2014
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Para Stereo?

One of the holes in my technical understanding of DRM is "Para Stereo."

As I type this, I am tuned to Kuwait's DRM signal (15540 kHz, Sunday 29/7/18 at 1915UTC). The signal is too low for audio decoding. Among the data on my MR27024's technical information pages is the fact that R Kuwait is broadcasting it in Para Stereo.

Does this mean that it is a monaural audio signal somehow processed by my receiver (were it strong enough) to make a *fake* stereo signal come out of my speakers? Does it mean there is a full dual-track audio signal carried by the DRM signal? Or does it mean something else?


I always enjoyed the AIR dual-channel signals I used to pick up until they killed that particular DRM broadcast (the one that shared 11620, 9445 and 7550 from time to time). That was not *stereo* in the sense of two channels for simultaneous listening.

Isn't a signal more robust (having to carry less information!) when it is mono? Why would any station on earth want to waste signal strength and coverage by including a stereo signal? Is that what is happening with "Para Stereo"?
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Old 29-07-2018, 23:29   #2
AF4MP
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Very basically the original stereo signal is encoded as mono on a bit stream with the missing stereo parameter information added as extra bits.

At the receiver the bit stream is decoded as mono audio and the stereo parameter info is then applied to produce the resultant stereo signal.

It actually works surprisingly well.

Some stations show on the Screen ID that they are transmitting P-stereo but unfortunately the content server is only providing mono audio and the resultant is no stereo, even though the transmitter is willing and ready to do so.
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Last edited by AF4MP : 29-07-2018 at 23:40. Reason: added last sentence.
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Old 30-07-2018, 00:59   #3
PhilipOneL
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Righto. So the "cost" of making a mono signal stereo is actually quite small -- do I have that right?
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Old 30-07-2018, 01:15   #4
AF4MP
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Yes, depending on the quality; for example, a 22 kbps mono signal becomes stereo with an extra 2 kbps.

DRM was designed from the start to be a higher quality transmission platform than standard AM and good quality stereo music on shortwave is really nice!
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Old 30-07-2018, 15:21   #5
PhilipOneL
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Thanks for the numbers.

I shall discontinue my mono-wanting curses at stations I cannot decode but whose ParaStereo signals are just below the threshold.
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Old 06-08-2018, 17:49   #6
F1BJB
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Quote:
Originally Posted by AF4MP
It actually works surprisingly well.
I totally agree.
Thanks for the explanation
In fact my opinion is that stereo was a bad idea from the start.
Twice the bandwidth for a very little improvement most of the time.
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