Swedish Radio at night

In the XXI century not all radio stations broadcast 24h a day. Some cease their programming after midnight and turn into a mysterious utility radiostations!

-And who'd have known it is also true for such civilised countries like Sweden! I first found out about this a couple of years ago during one night of excellent distant reception from Sweden in the FM radio band. Many Swedish stations were running their typical nighttime programing then (for example SR P3 joint with P4), but the First Channel after 1 AM started sounding strange. Sveriges Radio P1 is a speech channel, which means they usually broadcast news, current affairs and general talk shows. What I heard then sounded like a speech too, but somewhat processed...
Take a look:

Due to my acquaintance with pay-tv stations, I instantly recognised the "metallic" sound as an encrypted audio, the same I used to hear back in the days on analogue pay-tv channels. -Blimey, an encrypted programme in the middle of the night on the public Swedish Radio!

In this monophonic recording of SR P1 there are actually 3 streams: 1-kHz test tone - unencrypted, a separate programming on right and left channels, both scrambled - just the way you would hear them on any radio receiver.
The same "encryption system" was applied by Polish Canal+ and some other pay tv channels for scrambling their analogue broadcast (the accompanying video scrambling system was called Nagravision Syster).
Audio decoding was relatively simple - the entire soundwave spectrum was flipped at a given frequency point. As a result, bass tones were broadcast as high tones, and high tones - sopranos, as a bass. If you listened very carefully, you might guess what is being said, but music and other sounds were all messed up.

A decoder's job was only to flip the spectrum back. But it's a conditional access system, so the decoder would work only if some conditions are fulfilled - in the case of pay-tv, a subscription fee payed.
The "encryption" parameters were constant, so it meant easy piracy. And although sometimes there were problems with getting proper quality picture of Nagravision-encrypted channels using a "pirate" decoder, sound always worked out well. There used to be many plugins for computer soundcards to process a "crypted" audio.

Now, over 10 years after phasing out analogue scrambling, you might wonder why would a Swedish public radio provide such encrypted programming?

The scrambled radio shows run only at night, starting 1-2AM so I assume it's enough effort from Swedish Radio to preserve a casual listener from accessing it. So what is this programming? Who is entitled to listen to it then? And what are the terms and hardware for accessing?

A surprising idea for explaining the radio phenomenon may be found on this Swedish forum: http://elektronikforumet.com/forum/viewtopic.php?f=2&t=36768

The mysterious broadcasts is meant to be a "newspaper" for blind. A decrypting and recording device captures it overnight and in the morning the show is ready to play.
-Hmmm... Strange, since i always believed the radio itself (the unscrambled) is a newspaper to visually impaired people. Well... It must be some sort of "premium" service for blind.
Here's the original extract from the forum:

kodade "hemliga" sändningar på sr, och svt

rysshack.se
När jag var yngre kommer jag ihåg att någon gång då och då, så visades någon typ av kodade sändningar på svt. Man såg inte bilden ordentligt, och ljudet lät lite metalliskt, kanske lite förskjutet. Det gick inte att förstå vad de sa.
Nu satt jag uppe sent, och lyssnar på radio. Hör samma typ av ljud, när jag rattar in P1. Givetvis spelar jag in det. Kanske går att få ut något vettigt ur det med matlab.....
Någon som vet vad det är för sändingar jag talar om, varför de sänder kodat, och algoritmer för avkodning. Är det bara någon modulering eller något annat enkelt??

Jonyverse
Det du hört är DN eller SvD som taltidning för synskadade. De läses in och sänds ut kodat på natten till prenumeranter som har en speciell apparat med inbyggd P1-radio, avkodare och kassettbandspelare. När prenumeranten kliver upp på morgonen kan denne njuta av morgontidningen som alla andra.
Det har funnits ett tag och jag ägnade för några år sen lite tid med att försöka knäcka det hela.
Ljudet är modulerat på en bärvåg på runt 10-12 KHz och man tar ut det undre sidbandet och lägger ut på P1. Man kan faktiskt höra lite vad som sägs så för att dölja det spillet ligger det en "testton" (0,5-1KHz) och piper för att dölja och irritera tjuvlyssnare. Den används förmodligen som referens för att bilda ny bärvåg när man ska avkoda.
Jag lyckades avkoda med olika plugins i ett ljudredigeringsprogram i datorn, men enkel hårdvara går också. I signalen finns start o stoppulser för bandspelaren. Avkodning - filtrera bort tonen med högpassfilter, kör det som är kvar med en ringmodulator. -Klart ljud!! Om man bygger hårdvara, prova att faslåsa LO 10 KHz med en PLL på piptonen.
Kör hårt!
SM0NGL - Jonny

 

Also:
another report of "scrambled" Swedish radio fro ma DXer in Northern Poland: https://forum.radiopolska.pl/index.php?showtopic=1601