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Author Topic: Spitfire Am transmitter  (Read 2129 times)

Offline Kage

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Re: Spitfire Am transmitter
« Reply #30 on: March 04, 2020, 1808 UTC »
All of this music, for me, was listened to via AM radio. During the majority of the 70's I was in an area that wasn't served by any listenable FM station, so everything was AM Top 40 from local and at night, distant stations.  I have a certain affinity for the sound of AM radio. That's it. Carole King or Jethro Tull hit music sounds weird in pristine, clear, digital audio. I know it from AM. And I like it that way.
There is a certain sound to AM too. Even if you listen to the highest quality through a modulation monitor it still has a different quality to it than FM because of the methods used for broadcast processing.

That big and loud sound coming from either rack processing or StereoTool, once setup properly gives a punch that you just don't hear on FM and sometimes even further removed from the actual music source. Musicians hate this because their music doesn't sound the same on radio but to the listener it can be enjoyable because of the exact same reason.
Then there is the fact that some of the early rock music was actually mixed down in the studio with AM radio listeners in mind, so not only did they aim for HIFI listeners they also aimed for a sound that would suit peoples car and kitchen radios of the time.

I like to keep it simple and use an AGC to three band audio downward-expander/compressor into a mix of limiting and clipping. Finally with proper audio bandwidth brickwalling and compensation it can sound exactly like the big market stations of the 70s and 80s pushing maximum modulation or even into the positive with asymmetrical clipping for that huge sound.
Of course I like all of this to be analog and rolled my own gear to do so, but modern software replacements can achieve the same, or better. I find it best to not over complicate it and keep the audio path cleaner so not be fatiguing but loud enough to punch through the static and noise. Anything more than this might give you that giant market sound but it becomes overkill with a dozen pieces of gear or plugins running.

With mediumwave all your investment of time and money is going to be in audio and antenna anyway. Transmitters for the MW band are so cheap to design and even those Part 15 transmitters can get a huge improvement out of the two being their best.

Besides all of that, there is nothing wrong with enjoying nostalgic sounds. Get the most out of the medium and have the most fun with it!
« Last Edit: March 04, 2020, 1814 UTC by Kage »
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Offline M R I

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Re: Spitfire Am transmitter
« Reply #31 on: March 07, 2020, 1712 UTC »
I got stereotool to run on a pi4 and a hifiberry card last weekend.  Uses 1/3 the dc of my current processor, sounds good too 😊

+-RH

Hello Redhat. How is pi4/HifiBerry with Stereo Tool working? Do you monitor it with a display? Can you change settings or adjust levels. I know once set up it may not be necessary. How is the latency performance?

I think that is a nice application. I have been looking at the pi4/HifiBerry board also.

Although I could run Stereo Tool on a notebook also (low power compared to a large PC). I like the fact it is on a another dedicated device because of CPU usage and not on the main station PC.
Mix

Offline redhat

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Re: Spitfire Am transmitter
« Reply #32 on: March 07, 2020, 2031 UTC »
The end plan is to replace the current intel based machine running ST with the pi.  It would be neat to have a pop-out touch screen for changing parameters and such.  Latency is about 1/4 second, which isn't bad considering the  small amount of onboard processing power.  I've tried lowering it to 100mS or so and it wasn't real happy.  Good thermal management is a must, and even with the fancy case, CPU temp runs about 25 degrees C over ambient.  That is not much of a problem now, but might be when its outside in a rack and the ambient is pushing 40C.

+-RH
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Offline M R I

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Re: Spitfire Am transmitter
« Reply #33 on: March 08, 2020, 1724 UTC »
If Stereo Tool or another app with the same features is designed with the code to run on DSP chips directly you could get very close to (if not) zero latency. Not that latency is that important in a broadcast setup. 1/4 second is not that bad. Maybe someone will write a touch display code. Let us know how this project works out for you.
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Offline redhat

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Re: Spitfire Am transmitter
« Reply #34 on: March 08, 2020, 2018 UTC »
I was told that with ASIO drivers under windows it can be reduced to 20mS.  That said, bass distortion cancellation is reduced.  Long waveforms take time to process.  Even the delay in a modern optimod or omnia is on the order of a second or two.  The industry has given up on low latency processing for all things but talent processing, mainly because no one monitors off air anymore.  Thanks HD Radio...

+-RH
Somewhere under the stars...
WinRadio Excalibur/305 w/ a chi-town resonant loop, Kenwood KDC-U356 for mobile listening.
Please send QSL's and reception reports to xfmshortwave [at] gmail [d0t] com

Offline Brian

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Re: Spitfire Am transmitter
« Reply #35 on: March 08, 2020, 2226 UTC »
I was told that with ASIO drivers under windows it can be reduced to 20mS.  That said, bass distortion cancellation is reduced.  Long waveforms take time to process.  Even the delay in a modern optimod or omnia is on the order of a second or two.  The industry has given up on low latency processing for all things but talent processing, mainly because no one monitors off air anymore.  Thanks HD Radio...

+-RH
I don't think this is correct.
It's well under a second on any machines I use.

Offline chanito

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Re: Spitfire Am transmitter
« Reply #36 on: March 08, 2020, 2345 UTC »
22ms or less depending on mode for the Optimod 8700i.


Optimod 8600Si can go as high as 270ms for the MX presets.



25ms or less for the Optimod PC 1101e I use for ham radio. I can monitor my audio in headphones no problem.
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Offline redhat

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Re: Spitfire Am transmitter
« Reply #37 on: March 09, 2020, 0143 UTC »
FWIW, I have had very little contact with the newer boxes, and most of what I've heard is second hand or from sales reps.  The point being is that few folks are monitoring off air these days and latency is less of a priority.  Add to that in the typical airchain the processor is only one source of latency.  Often the STL path is far from instantaneous, and most of the newer AOIP routing systems have some delay as well.  30-50mS seems the be the break point where it becomes hard to use in a live situation, and by the time you approach 100mS I can't use off air monitoring.  The effect is weird, you start to stutter!

Running HD?  8 seconds minimum coding and buffering delay for most HD systems.  I believe DRM has similar delay, perhaps less.

Anyway, sorry to derail the topic.  Perhaps we could pick this up somewhere else.

+-RH
Somewhere under the stars...
WinRadio Excalibur/305 w/ a chi-town resonant loop, Kenwood KDC-U356 for mobile listening.
Please send QSL's and reception reports to xfmshortwave [at] gmail [d0t] com

Offline Pigmeat

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Re: Spitfire Am transmitter
« Reply #38 on: April 02, 2020, 1224 UTC »
I based a station based around the early surf rock innovator, guitar player, Dick Dale. I do an "id" and the coyotes started howlng. I go into "Hava Nagila", they're going wild, into "Miserlou, and in two car loads of teenagers come barging in. I was very tempted to show them what a couple of loads of buck and ball would do their radiators, but I think they'd figured out by then that an armed older guy in sticks with a backpack meant he was placing meth labs.

I wish I had an aircheck of a mid's 90's one two liter bottle meth lab going off. They sounded just like the mines John Wayne miraculously managed to dodge as both a Marine and as a Green Beret