Old 08-18-2011, 12:32 PM   #1
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Default Realistic AM-radio simulation with REAPER

These projects attempt to simulate AM radio in most of its characteristic effects by "macro-modeling" the actual signal chain from transmitter over ionosphere to receiver and speaker, recreating the interdepency of on-channel and off-channel signals in the receiver.

This goes way beyond simple filter and distortion type of AM simulation, it recreates most of distance-related detrimental effects of AM radio like characteristic intermodulation and distortion effects created by off-channel signals, multipath propagation/selective fading and in the (cheap) receiver frontend. Yada.

You can get the unspectacular local clear-channel station sound which doesn't differ much from what already exists, and - this is where this probably differs most from what I've heard so far - get a quite realistic representation of a station transmitting from 10,000 miles away on a particular shortwave band.

Typical offchannel signals/interference are created in realtime. In addition to that special noise, you can simply add audio files on the "splatter" tracks in order to create a realistic frequency neighborhood, they will rock your virtual IF filter slopes almost like the real thing.

The bottom line is, when you need an AM sound that won't get debunked as "bandpass with distortion" by every radiohead/ham/SWL/old guy within 20ms, this is supposed to do it.

Demo*: night reception of a medium power station, 500 km away, on the European broadcast band. Please note how the mysterious station fades into a longer "propagation hole" in a (hopefully) very typical way after about half a minute.

*Parts of the clip courtesy of Drew or SWS or someone else in the reaper chat, sorry it's been a long time...

Here are the projects:

1. AM Radio Sim 41m Evening (shortwave)

A strong shortwave station heard on 41m in the evening. 41m is a traditionally crowded band with strong ionospheric signals from medium distances. Check this project first, it demonstrates best where this simulation is unique (or wrong! )

2. AM Radio Sim BC Europe 150km (AM broadcast band)

Not a local medium wave station but still strong and with a slow fading setting in as it's typical for evenings, when the ionospheric waves start mixing with the ground wave signals. Interference and bandwidth match the European 9kHz-channel situation during that time of day.

If you're not into this stuff and need a specific situation modeled ("I need the sound of a particular station/time period/frequency band") anyway, just post here.



How to use:

All you need to do is to slap an audio file on the Program/TX track. If you want some (different) audio files of your choice to create stations transmitting on the adjacent radio channels ("splatter"), to add your own neighbor stations to all projects, just replace the files on the "Splatter USB" and "Splatter LSB" tracks.

In both projects you can move away from or go closer to the station if you will, by changing the "Fading Server" fader - the more you move it towards 0dB, the more intense the fading and interference becomes and pulling it down around and beyond -10dB makes the stations "local" or "pretty close", or relating to the frequency, either more "noon" or more "midnight".
The leftmost track on the MCP is a "signal strength meter" where you can see the effect. All other controls can easily destroy the "simulation" character to something rather unrealistic, so I locked the controls. Please unlock and play at own risk and don't blame me if you open a wormhole by accident.

If you disable the "speaker" FX chain on the master, you will get something like a less filtered "headphones" or "line out" type of signal as a sound alternative. The "Transistor Radio" EQ on top of the master chain shrinks your radio in an instant.

Since the free running part of the mass of LFOs in the project are starting from playback start, it's best to start renders 30s (they are slow LFOs) ahead in time in order to let the LFOs phases run apart. In general, the longer it runs, the more realistic it gets.



How it works:

I used REAPER's great parameter modulation and an additional pair of track channels to introduce a "control voltage" solution to recreate the actual "when X goes up, Y must come down" mechanics of signals in a radio:

For example, "fading" is an elementary component of AM radio. Unless your station is very close to you, its signal strength will have cyclic variations, with their intensity depending on distance, propagation conditions and power, which can result in a station changing between "full power signal" and "dropping below the noise carpet" all the time. This action is compensated by the "AGC" (automatic gain control) in your receiver, which increases receiver input stage gain when the signal drops, which in turn causes the noise and interference to come up.

Creating a realistic AM sound with only audio signals suffers from the lack of a carrier (RF-) signal that determines all other events in this manner, but this is easy to do in REAPER and so the simulation uses an actual "signal strength" concept to control onchannel and offchannel signal levels, fading and the receiver AGC. All tracks with a "Fading Client" (which is just a JS volume plug-in) are depending on "signal strength".

The on-channel signal runs then through a "Ionosphere", how that works probably explains itself best by opening the FX chain window for that track. The actual theory is that multipath propagation with runtime differences between the paths is causing an effect called "selective fading" amongst radio guys, in our circles better known as "phasing". This has some little twists and turns though, one of them being that it resembles a "barberpole" or "Shepard's tone" movement (which is why you can't do it with a phaser). The effect can be so spectacular (in real life) that it made me wish I could have the ionosphere as a stomp box.

Unless you're listening to a "clear-channel" station (which only exist in the USA), there is a high likelyhood that the channel neighbors are causing "splatter" - their modulation is bleeding through, with a low frequency rumble from one side of the frequency scale and with a high-pitched rustle from the other side and their carrier signal may be one source of the typical "interference" or "beat frequency" tones you hear on AM. I used heavy filtering and a ringmodulator to create the splatter signals from anything sitting on these tracks. Interference noises (each underlying its own fading) are created on the "Beat Frequency" track using a bunch of tonegenerators.

In short, it's not perfect but it tries to be and I hope that it's as close to AM radio as it gets in your computer.



Can this guy get a real life or what?

This is definitely a trip to geekland and a realistic simulation of how things get unintelligible on AM is not what Hollywood will let us hear in a flick, but it may have some limited practical use (and you still can turn down the "Fading Server" track to get a boring but still accurate AM sound)

- You can check how your tunes or your commercials/jingles turn out on AM radio when it reaches an audience nnn miles away. This can be a revealing thing regarding your mixes, which will suffer from bandwidth limitation, being mono, masking effects and the brutal effects distance and propagation conditions can cause. Can your spot/speech/message/arrangement survive this?

- If you happen to like that old AM sound, you can listen to your own private station all day by streaming audio through the "Program/TX" track, or fake old time radio show recordings in adequate realism.

- Maybe you could make experiments with processing signals going to an AM radio transmitter. I tried to create some generic processing chain in a very uneducated way, but maybe it is of some use to have something like a playground for technical purposes like this.



Edit 08/29/11: I updated the archive with new/alternative versions of the projects: I overheard that AM transmitters never get a bandwith limited audio signal except for some occasional 50Hz rolloff maybe. So it bothered me that I needed lots of ReaEQs on the wrong places (e.g. the transmitter) to get the needed "offband rejection" in the receiver.
Pretty much all of the bandwidth limiting is actually done by the IF filter and other receiver parts, so I needed to create a better one in ReaFIR that can do the job all alone, which is more than easy, I can rebuild actual IF filter shapes and so I upgraded your receiver with a pro grade Collins filter. I further added some multiband processing I suspect to find in actual signal paths to transmitters. I would love some input from technicians there.

Last edited by Ollie; 09-04-2011 at 02:57 PM. Reason: spelink and gramar r not my friendz
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Old 08-18-2011, 01:35 PM   #2
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Interesting stuff.

Thanks.

On testing this I get a "leveler" and "mod optimizer" FX not found.
Where do I get these ?
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Old 08-18-2011, 01:41 PM   #3
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They''re just renamed (in REAPER that is) instances of ReaComp, that's odd that it doesn't load them... (but apparently the other renamed stock-FX)
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Old 08-18-2011, 01:58 PM   #4
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Before testing this I just did a fresh portable install (using default tickbox settings).
Now upon rechecking, ReaComp was the only FX that was unticked.

I wonder why that is, but this explains it.

After reinstalling with ReaComp included it loads fine now without missing plugins.

Thanks.
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Old 08-18-2011, 02:08 PM   #5
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This happens relatively often these days and I start thinking these things really uncheck themselves... are you sure you didn't uncheck that by accident?
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Old 08-18-2011, 02:34 PM   #6
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Eat your heart out Tom Waits!

I love this stuff! I'm on my phone now but will check it out this eve.

Thanks Ollie.
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Old 08-18-2011, 02:44 PM   #7
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Dang now I have that song in my ear and it won't get out!
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Old 08-18-2011, 03:36 PM   #8
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Boy, that's plain crazy!

Ok, I need sunshine along the day tomorrow and a healthy chunk of rain in the evening. Which faders do I automate for that?

Amazing work, Ollie.
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Old 08-18-2011, 04:12 PM   #9
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Very cool Ollie - although I barely understand how this works. Thanks for posting, I am pretty I'll use this on one of my projects.
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Old 08-19-2011, 03:03 PM   #10
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Quote:
Originally Posted by gofer View Post
Boy, that's plain crazy!
Thanks! In case you meant that in a more literal way, I know...that's so nerdy I'm giving myself wedgies all day.

Quote:
Originally Posted by peter5992 View Post
Very cool Ollie - although I barely understand how this works. Thanks for posting, I am pretty I'll use this on one of my projects.
Thanks! I tried to make sure you don't really need to understand how it works (hence the locked tracks and a single control for the intensity of the effects), but I edited the OP a bit.
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Old 08-21-2011, 10:30 PM   #11
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Outstanding effect! Takes me right back to the 70's. Give yourself
a wedgie on me, my treat
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Old 09-07-2011, 07:29 AM   #12
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I appreciate a project like this. Kind of a perfectionist vibe that tickles me. Now maybe I can do my remake of Pink Floyd's Wish You Were Here.

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Old 01-28-2012, 04:25 PM   #13
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Ollie you are a star! Very realistic indeed

I am a radio engineer by trade, hobby musician, radio ham (as well as a sometime DJ) and have been contemplating something like this for years! - wanting to recreate the time spent as a youth listening to 'The Peter Stuyvesant top 30', circa 1973 on 1440 Radio Luxemburg, or , 'from a point at sea, to the circles of your mind' ...., 319metres, 962 kHz This is the new Radio caroline...'

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Old 07-31-2013, 12:59 PM   #14
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Amazing support guys! So many possibilities I don't know where to begin. I think I'll go eat some chocolate
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Old 08-29-2013, 04:37 AM   #15
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Default thanks ollie for reminding me

Ollie,

Just a quick thenk you for reminding me that all audio is.....is manipulation of time, freq and amplitude. i checked out a couple of your projects on reasynth......I love trips back to the basics.....Thanks again


The paramater modulation on THA is absolutely inspiring to me.
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Old 08-29-2013, 08:00 AM   #16
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Default Scary Good

I was just talking about this with a ham a few weeks ago! Thanks for mindreading.

It's scary good. Is there a way to simulate tuning the receiver? It would make the whistles and such change frequency.
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Old 08-29-2013, 08:05 AM   #17
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Outstanding

one question...

Does it simulate a "Realistic" (TM) radio, or does it just sound real? :cheeky:
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Old 08-29-2013, 09:45 AM   #18
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Quote:
Originally Posted by toddhisattva View Post
I was just talking about this with a ham a few weeks ago! Thanks for mindreading.

It's scary good. Is there a way to simulate tuning the receiver? It would make the whistles and such change frequency.
I wouldn't say "no" but given the complexity of the whole thing it would be utterly complicated to synchronize stuff to simulate tuning in a similar depth. Interesting food for thought tho.

Quote:
Originally Posted by James HE View Post
Outstanding

one question...

Does it simulate a "Realistic" (TM) radio, or does it just sound real? :cheeky:
If you tweak the "IF filter" accordingly to simulate some super-cheap knock-off of a cheap Murata ceramic filter and add a few tracks to recreate bad image rejection and/or an easy to overload input stage, you'll get a realistic Realistic.

(Had DX-394 for a while, it looked much better than it performed and may not be representative for all Realistic radios. After all IIRC they made some rather good BC band DX receiver in the 70s, forgot the name.)
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Old 02-09-2016, 05:13 AM   #19
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I'm totally newbie with Reaper, I found this topic making a google search of a VST plugin that would make a (random) distorsion like short wave reception.
So, I just installed Reaper, download the project and run : very nice and realistic

One question :
How can I add (random ans cyclic) distorsion to the track "program/tx" ?
I guess it will ask some serious knowledge ...
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Old 02-09-2016, 09:54 AM   #20
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just stumbled upon this thread because it popped up under "new posts".

very interesting.

and what is that in the demo??? Obama saying "Reaper is da shit!"?

bruhahaha...
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Old 02-09-2016, 10:13 AM   #21
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Quote:
Originally Posted by LightOfDay View Post
just stumbled upon this thread because it popped up under "new posts".

very interesting.
Same here. This grabbed my attention immediately. My first qualification when I completed my apprenticeship 25 years ago is "radio tradesman" so this is right up my alley.
My first job (before I started my apprenticeship) was working at an AM radio station called 3GL in Geelong which is now called K Rock and is now on the FM band.
I've just downloaded these projects and will give them a whirl tomorrow.

Last edited by ReaDave; 02-09-2016 at 10:22 AM.
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Old 02-09-2016, 10:21 AM   #22
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Here's a photo of the AM transmitter from 3GL where I worked nearly 30 years ago. Those output tubes visible in the left hand window panel are as tall as the average person!

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Old 02-09-2016, 10:35 AM   #23
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I couldn't wait until tomorrow. Playing about with this now. This is VERY nice work Ollie!!
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Old 02-09-2016, 12:14 PM   #24
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nice Even the president agrees!
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Old 02-09-2016, 01:11 PM   #25
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This thing is the ultimate in nerdy coolness. Bravo sir.
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Old 02-09-2016, 02:20 PM   #26
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Quote:
Originally Posted by ReaDave View Post
Same here. This grabbed my attention immediately. My first qualification when I completed my apprenticeship 25 years ago is "radio tradesman" so this is right up my alley.
My first job (before I started my apprenticeship) was working at an AM radio station called 3GL in Geelong which is now called K Rock and is now on the FM band.
Wow! Takes me back to the late 50s - early 60s. 3GL all over the dial on all the crystal sets I made, blocking out most of the Melbourne stations. If I'd understood tuned circuits when I was 15 as I did (still do) a few years later as an Electrical Engineer, I'm sure I could have done better.

Managed to spend a bit of time with a technician at 3GL while I was studying. Mostly making a nuisance of myself I suppose.

Still often listen to K-Rock via the internet during the footy season.
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Old 02-09-2016, 03:07 PM   #27
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Old 02-10-2016, 08:07 AM   #28
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Thanks everyone for your nice comments! I've almost forgotten about this thing.

Quote:
Originally Posted by on4lao View Post
One question :
How can I add (random ans cyclic) distorsion to the track "program/tx" ?
I guess it will ask some serious knowledge ...
The more you push the "Fading Server" fader up (more "Fading Server"=more fading), the less signal strength and the more random and cyclic distortion you will get, in conjunction with the signal dropping into a fading "valley".

I must admit that I have no clue anymore how or where exactly that distortion was introduced, so I can't give you any hints on how to control that further.

If you want to make the "output" of the "transmitter" more distorted, just slap some distortion on the "Program/TX" track, however (much) distortion added at that stage is not what usually happens unless the transmitter is seriously ill.

Last edited by Ollie; 02-10-2016 at 08:13 AM.
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Old 02-10-2016, 09:12 AM   #29
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Quote:
Originally Posted by alanofoz View Post
Wow! Takes me back to the late 50s - early 60s. 3GL all over the dial on all the crystal sets I made, blocking out most of the Melbourne stations. If I'd understood tuned circuits when I was 15 as I did (still do) a few years later as an Electrical Engineer, I'm sure I could have done better.

Managed to spend a bit of time with a technician at 3GL while I was studying. Mostly making a nuisance of myself I suppose.

Still often listen to K-Rock via the internet during the footy season.
I hoped you'd spot this topic Alan.

Here's a blast from the past for you. I remember this like it was yesterday!!!
3GL on the West Coast jingle
https://soundcloud.com/retroradio-1/...coast-jingle-1

Brings back memories cleaning the cart machines they used to play those jingles.... and the morning routine of cleaning and demagnetizing the Ampex open reel news decks and broadcast logging decks.

I can relate to your experiences with crystal sets too. I did the same thing and had the same results. 3GL loud and clear no matter what the tuning!!! I lived in Grovedale at the time and the 3GL transmitter was only a few blocks away from us (in Heyers Road).

I have fond memories listening to the Cats on 3GL in the mid 80s on an AWA Radiola valve radio in our garden shed next to the swimming pool on hot summer days. That radio my Dad got from his Dad and he still has it. It isn't working at present but next time Dad visits (in a couple of months), he's going to bring it with him and I'm going to see if I can restore it. Perhaps I should make a post about that if anyone is interested in following it.

Do you remember the name of the tech you worked with at 3GL by any chance?

Here's an interesting site with some info about 3GL and its STC transmitter from 1970...

http://users.pipeline.com.au/~burst/stc.htm

...and a cool photo of the transmitter from that site...


Quote:
Originally Posted by Ollie View Post
Thanks everyone for your nice comments! I've almost forgotten about this thing. .....
You've created a real gem there Ollie. I spent considerable time last night running all sorts of things through that simulation. It had me totally captivated!! I played around with some ReaEQ settings on the audio output to simulate more closely some of the old transistor radios I had as a kid. I also added a 10KHz whistle filter on the output with just enough attenuation to simulate the filters on some of the better AM receivers (they were 9KHz here in Australia).

Your work on this fantastic emulation is inspiring some new musical ideas for my next album too.
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Old 02-10-2016, 09:59 AM   #30
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Cool! Didn't see this thread originally so glad it came back around.

This should be good stuff the next time I have the opportunity to make a "Pink Floyd" cinematic mix.
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Old 02-10-2016, 10:49 AM   #31
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Quote:
Originally Posted by Ollie View Post
Thanks everyone for your nice comments! I've almost forgotten about this thing.



The more you push the "Fading Server" fader up (more "Fading Server"=more fading), the less signal strength and the more random and cyclic distortion you will get, in conjunction with the signal dropping into a fading "valley".

I must admit that I have no clue anymore how or where exactly that distortion was introduced, so I can't give you any hints on how to control that further.

If you want to make the "output" of the "transmitter" more distorted, just slap some distortion on the "Program/TX" track, however (much) distortion added at that stage is not what usually happens unless the transmitter is seriously ill.
Thank you Ollie for the infos, I'll make some try
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Old 02-10-2016, 11:36 AM   #32
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AllanOfOz, this is especially for you. I just ran the 3GL jingle through Ollies AM radio emulation.

First pass is through a full range mantle style radio. Second pass is through a cheap transistor radio.

3GL on the West Coast - Ollie Style
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Old 02-11-2016, 04:47 AM   #33
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<Warning - nostalgia>
Dave, Thanks for all that, especially the STC stuff - I would have loved some of those pics when I was teaching this stuff through the eighties.

The jingle was new to me - a bit after my time there. Good job on the radio emulation - can it emulate a crystal set with old army disposal headphones? I lived in Elizabeth St Belmont back then, so not much further from the transmitter than you were.

From '61 to '64 I studied Electrical Engineering at the Gordon, so I often passed 3GL, must have been Little Mallop St. Back then it was the Gordon Institute of Technology (not the current Institute of TAFE). One side of the tracks was effectively the technical college, the city side was as good as an offshoot of RMIT, although we liked to think we were independent. When Deakin Uni started some years afterwards many of the courses and lecturers went there, (much simplified version).

During my student days a fellow student (name forgotten) had a family member (or family friend) working at 3GL as a technician. He seemed to me to be close to retirement (but at my age then anyone over 50 probably seemed that way). Can't remember his name. One day I blew a resistor in my multimeter, which had cost me a whole weeks wages of my holiday job. The replacement resistor (same price as a milkshake I couldn't afford) seemed to result in questionable readings, so my mate took me to see this technician for the first time. Using 3GL's Post Office Box we determined that what should have been 470 ohm was 493 (can't remember names, but I remember the value). Making practical use of my course I calculated that 10k in parallel would get very close to 470. Also that a poor tolerance on the 10k wouldn't matter much. I skipped another milkshake & bought the 10k. Still have the multimeter.

The PO box was a bit like this


I moved to Adelaide in '65 to work for Philips at Hendon, a couple of years later to Sydney, later at EMI, then teaching electronics for 40 years at technician level. Then retired to the Blue Mountains. Never been busier.
</nostalgia>
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Old 02-11-2016, 07:10 PM   #34
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Thank you for reviving this thread. thanks Ollie of course for sharing the concept, and thank you ReaDave for the example you provided. Definitely nostalgian sounds, well done.
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Old 02-12-2016, 01:46 AM   #35
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Initial Project from Ollie - AM_Radio_Sim_41m_Evening_3000mi.RPP

I've changed the original splitter.mp3 file by a shortwave RTTY broadcast reception.
Also, some adjustement in the volume ( in db) :

OnChannel 0
Program TX 1.09
Fading Server -6.5
Channel Noise 0
QRM Master 0
Beat Frequen Mute
Splatter LSB -18
Splatter USB -5.5
Multipath Del -27.4

A small extract https://stash.reaper.fm/26637/Carolin...0RTTY2%20X.mp3

Thank you, Ollie, for this nice project
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Old 02-12-2016, 08:04 AM   #36
cyrano
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Hey, I like that! Mind if I borrow it?
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Old 01-24-2017, 06:36 AM   #37
audionomio
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Default Thank you!

I just registered to express my huge THANK YOU! This is a real gem, I was looking a realistic AM simulation already for a very long time. Once I even built a complete AM transmitter/reciever chain to get that sound. But in this current project this is no option, so I need to simulate it. And it works really beautifully!

Thank you so much for sharing it!

Bests,
- mathis
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Old 02-01-2017, 10:07 AM   #38
ReaDave
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I'm currently working on a new album and will be using this simulation (with a few of my own mods) for sections of the album where I'll be adding narration.
I wanted the effect of someone tuning in to a distant station and hearing the narration which will lead into various sections of the album.

One thing the simulation doesn't do though is simulate the tuning of a station. So, in order to achieve that, I've just built a very crude AM transmitter using a single 555 timer IC (those little chips are EXTREMELY versatile) and a few other components to transmit to my 80s ghetto blaster (which I've had since the 80s).
I'm feeding the output of the REAPER simulation to the input of the transmitter and will record the audio from the ghetto blaster headphone socket back into REAPER.

I've just run a test and it works really well. The AM transmitter, as mentioned, is very crude and the signal is somewhat noisy but in this case, that only enhances the realism.

Here's a couple of photos of the transmitter (built on a prototype breadboard) and the ghetto blaster.



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Old 02-01-2017, 11:12 AM   #39
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This stuff sounds fantastic... Wow. Thank you!
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Old 02-01-2017, 02:31 PM   #40
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that's a hell of a ghetto blaster readave.. dave
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