link studio

Everything technical about radio can be discussed here, whether it's transmitting or receiving. Guides, charts, diagrams, etc. are all welcome.
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radium98
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link studio

Post by radium98 » Tue Mar 14, 2017 6:34 pm

COULD here help to make an STL LINK ? any band 9filter ,if and vco ,pll for rx)

nrgkits.nz
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Re: link studio

Post by nrgkits.nz » Thu Mar 16, 2017 6:30 pm

Use a pair of Ubiquiti PowerBeams, they'll easily do 10km line of sight. It's an IP link so use streaming software like icecast2 to carry audio, you could use raspberry pi's at either end and run stereotool at receiving end to feed a MPX signal to the tx.

radium98
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Re: link studio

Post by radium98 » Thu Mar 16, 2017 7:57 pm

thanks :)

alfaeire
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Re: link studio

Post by alfaeire » Fri Mar 17, 2017 9:44 pm

We use ubiquity for ours, raspberry pi on the tx end, so the pi is on our studios network. Then we encode our audio and the pi plays it in Kodi / Xbmc via an ip address. Just need to get a splitter to break down the hdmi, take the audio from that and it will be high quality.

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Albert H
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Re: link studio

Post by Albert H » Sat Mar 18, 2017 3:47 am

I used a Raspberry Pi with a PhatDAC board to recover the audio. It'll run at 96 kHz so it's fast enough for stereo, but not quite quick enough to include RDS, so I use a separate RDS PIC in the rig. I'm waiting for a newer version of the sound card which will be able to do 192kHz which will allow RDS and a lot of other goodies too.

The PI Zero has really changed the whole game - a cheap sound card connected to a £10 computer, with a £2.50 micro SD card, and you have the whole digital link receiver in a tiny module. I've also got an "Orange Pi" which is even cheaper - this might prove to be the best solution for "throwaway" gear!
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radium98
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Re: link studio

Post by radium98 » Sat Mar 18, 2017 2:04 pm

:( zero

nrgkits.nz
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Re: link studio

Post by nrgkits.nz » Sun Mar 19, 2017 8:50 am

You could also write some "phone home" software or a simple bash script and put it on the receiving Pi, anything that will allow you to issue remote bash commands on the device and take remote control of it. Then in case of a rig thief or the Pi mysteriously walking to another station, this could be very useful. You could also use it to infiltrate their local network.

g2000
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Re: link studio

Post by g2000 » Sun Mar 19, 2017 7:26 pm

Does raspberry pi3 have enough CPU to have stereotool doing processing? I presumed not, so have been trying my hardest to get stereotool running on my VPS, then streaming MPX via flac stream...

Would also use a reverse SSH tunnel to have the pi connect back to my VPS so that I can SSH to it really easily, regardless of NAT and firewalls etc!

Albert H
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Re: link studio

Post by Albert H » Sun Mar 19, 2017 8:24 pm

I've run Stereotool on a Raspberry Pi 3. You have to stop pretty much every other process, but it works quite well!

There are alternatives to Stereotool but they're harder to use and don't (usually) have a GUI interface - you have to configure them using text files. When I've confirmed the efficacy of the solution that I'm working on at the moment, I'll post a link to two image files which you'll just write to a blank 8Gb Class 10 SD cards, plug them into your two R P1 3s, connect the AD card at the transmit end, and the DA card at the receive end...

Link using your favourite medium ('net, Wi-Fi, p2p, or whatever works for you), feed your suitably processed studio output (compressed, limited, pre-emphasised) into the TX inputs and recover composite MPX at the RX output socket to feed into your rig.

The configuration files will only have to be written to the TX end (any remote settings will be promulgated over the link). You should be able to get a secure, high quality link for well under £100 if you're using Wi-Fi, about £300 if you use the Ubiquiti PowerBeams.
"Why is my rig humming?"
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g2000
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Re: link studio

Post by g2000 » Sun Mar 19, 2017 11:26 pm

I'm more of a terminal person than a gui one!

Unfortunately I've not managed to get the Linux stereo tool command line version to output mpx for some reason (no trouble with Winamp dsp version with same preset file!) - currently trying to output to file while I'm getting it going.

Are you suggesting you're using other apps besides stereotool for the compression, preemphasis, and mpx?

I'll be adding a relay board to mine, so I can have a cron job to power on/off the transmitter

Albert H
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Re: link studio

Post by Albert H » Mon Mar 20, 2017 8:25 am

My processing air chain is entirely analogue. The compression uses a feed-forward circuit with BBD ICs in the audio path to eliminate the attack time. The pre-emphasis uses a gyrator-based circuit to also provide a really steep 15kHz lowpass filter. The limiter also uses BBD based feed-forward also, so it doesn't overshoot, pump or require clipping. By means of a few other little processing tricks, I can get an output that sounds "loud", but isn't fatiguing to listen to - it just sounds "right". There's also no clipping whatsoever in the chain - I don't like adding deliberate distortion to my audio!

The man from Orban couldn't understand that no matter what he tweaked on his outrageously over-priced processor, he just couldn't get anywhere close to my subjective "loudness" without severe distortion.

If you want guidance on the design of an analogue processor, take a look at the circuit of the Innovonics "David III" processor. I was very involved in its design, so you can see some of the approaches I use. The David III does use clipping, but uses distortion cancellation to minimise the damage it does.
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g2000
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Re: link studio

Post by g2000 » Fri Mar 24, 2017 9:22 am

@AlbertH

Sounds good - and less software to crash or go wrong!!

I've just got a 'JustBoom DAC' for the pi 3 so that I can output at 192kHz. Trying to get StereoTool running on the latest Raspbian image... What did you need to do to get it working?

- I've added the soundcard stuff into config.txt, so that should be ok...
- I *think* i''ve got jackd2 running correctly, but not sure on what cmdline params are needed here. Oddly, jackd2 is v 1.9.x
- I then use mplayer, outputting a stream into jack
- start up stereotool, it doesn't companin about jackd not running, so presume all good so far...

Current show stopper is in stereotool, when i look for inputs and outputs, nothing is listed, just a red box?

Will try and have another bash over the weekend... Would be rather lovely to do away with the laptop at TX site!!!

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