AM Audio processing on a super low budget

[darklife]

I am tinkering around with a small AM transmitter that I built. It's modulated using series transistors so the audio has a flat frequency response much like more complex and expensive transmitters do.
From 25Hz-15KHz the audio is flat and just feeding it audio from some good music is amazing sounding on good AM radios
What I am curious about is how to get this thing sounding professional w/o spending the money on expensive multiband compressors and such.
Would a simple equalizer and mono compressor be enough?
Is there any free or shareware software out there to process audio for AM?
I'd love to see what this thing would sound like if treated with proper audio since it's capable of 100% modulation w/o distortion.
Should I really cut everything off above 10KHz? I know it's the NRSC standard for legal broadcasters but not sure if part 15 operators or hobby broadcasters do that also.
Just some basic audio tips would be helpful. I have no money budget right now so any software to emulate what hardware would do would be great.
I am fluent in building electronics so any schematics to simple audio filters or circuits for AM processing would be appreciated.
You can check my website for pictures and schematics of the rig I built for experimental fun.
Thanks a million guys.

 

[Tom Wells]

How little is cheap? I also was going for maximum clean, but went the vacuum tube route, modulating on the grid of a 6SN7.
You don't need to follow the NRSC rolloff, or limit your max upper end with part 15. Go for flat.
I use an ART Pro VLA, which is somewhat helpful, $300, but nothing to write home about.
You can set the two channels up unlinked, then run through 2 passes seperately, where the first has an infinite ratio
to limit quick peaks, and the second pass at 3:1 ratio or so, for some gentle compression.
Nice, but still not going to sound like a professional setup.
If you can scrape up enough to buy a used computer, do so, then buy Breakaway Broadcast Processor software.
It is worth every dollar and sounds like it costs many times more. It was 200 dollars a few years ago.
Other alternatives are to buy a used broadcst processor, you will find many recommendations from many different viewpoints, and a lot there depends on personal preference, how you think your music ought to sound, and what kind of music
you'll be running through it.

It is important to have multiband processing, otherwise, you'll hear interaction and ducking that won't sound right.
Not terribly important just how many bands, but you need at least three.

 

[darklife]

Thanks for the reply so far. I was fiddling with the sound while wired into a dummy load and listening to various receivers in my house.
I guess that I really can't go with the NRSC standard anyways. Even though my transmitter is fully capable of 25hz-15khz flat the roll off is right around 10k anyways and when I crank up the highs I cause the lows to be more subtle if I try to avoid distortion. In fact some of the 1-5k frequencies seem to steep above the levels that should be sustainable. I play one song and it sounds great, play another and it sounds awful. Starting to wonder if it's my setup or the music not liked to be mixed in monotone and clipped at 10k.
I don't have the money for a multi-band compressor. That's why I asked if there is alternative solutions.
If I apply the EQ it just takes the highs down another notch and normalizes the bass.
I don't have professional equipment to see the actual spectrum analyzation in action.
I have plenty of used computers. Problem is the breakaway software is pricey and not free. That's why I was suggesting and asking if there is alternative ways to go about it.
I have been an elecro DJ for a short time and seen some of the plugins you can add to the audo stream. I don't see why it's not impossible to just add three individual compressors using a client like fruity loops studio or something and then just running them live and compressing bands of frequencies much like the pro gear does only w/o having to pay a fee.

 

[Charlie]

MBL4 (from the author of Sonos) is a good freeware processor - it features Gate, AGC, 3x Compressor, Limiter plus In/Out LPF/HFP and adjustable Pre-Emphasis. You can also apply "AM" and "FM" filtering on the input (to ease the processor work) and/or the output. It'll run as a stanalone program - you'll need 2 soundcards to "record" the first into MBL and output it using the 2nd. Or you can use 1 card if you're recording the line input. It will also work as a DirectX plugin - so using AdaptX you can run it in something like WinAmp or WMP. As well as "live" sound via a soundcard it will also "play" a file direct.

In comparison to something like the Breakaway Processor, MBL is quite "dull" - the later "Sonos" product is also worth a look.

Screenshot: http://www.charliedavy.co.uk/mbl4.png

If you can't find a copy of it I'll put it on my site for you.

 

[Tom Wells]

If you have some old computers to spare, bite the bullet and save up for Breakway, or at least try out the demo version
of both Breakaway Personal at 40-ish bucks, or even run the trial Broadcast version and be PROUD of your sound while the
demonstration Promo runs. The author included many tweaks specifically for AM, such as 150% positive modulation peaks,
and I promise you will be stunned if you spend some time playing with it. You will thunder and pound like the biggest
50kw blowtorch you've ever, ever heard and never look back at the price.
I'm using an old IBM thinkpad circa 2005, feeding into consumer gear, and my 100 mw sounds like WLS and WCFL on a hot summer night in 1968. I'd spend the money again in a heartbeat. The oscilliscope doesn't lie, you should see how the thuds and crunches fly up to 150%, while never pinching off. And song to song, from classical to punk, everything stays well controlled. I never have an urge to tweak eq since making the change. It all sounds effortless and a proper balance
is maintained despite songs with different eq balance and levels.

After you demo it, you will see your way clearly to buy it. Save the money somewhere else and give your ears a treat.
Did you download the aircheck in the other thread regarding diode detection for air monitors?
How about that "Java" by Al Hirt at the end?

 

[OKCRadioGuy]

http://www.rdlnet.com/product.php?page=242

Run that audio into something like an Inovonics NRSC filter/peak limiter and you're good to go. There seems to be plenty of those old NRSC filters generally laying around stations as they move up to better processors, etc.

It's cheap and it sounds great. ;D

Good luck.

 

[BobOnTheJob]

If you have some old computers to spare, bite the bullet and save up for Breakway, or at least try out the demo version
of both Breakaway Personal at 40-ish bucks, or even run the trial Broadcast version and be PROUD of your sound while the
demonstration Promo runs. The author included many tweaks specifically for AM, such as 150% positive modulation peaks,
and I promise you will be stunned if you spend some time playing with it. You will thunder and pound like the biggest
50kw blowtorch you've ever, ever heard and never look back at the price.
I'm using an old IBM thinkpad circa 2005, feeding into consumer gear, and my 100 mw sounds like WLS and WCFL on a hot summer night in 1968. I'd spend the money again in a heartbeat. The oscilliscope doesn't lie, you should see how the thuds and crunches fly up to 150%, while never pinching off. And song to song, from classical to punk, everything stays well controlled. I never have an urge to tweak eq since making the change. It all sounds effortless and a proper balance
is maintained despite songs with different eq balance and levels.

After you demo it, you will see your way clearly to buy it. Save the money somewhere else and give your ears a treat.
Did you download the aircheck in the other thread regarding diode detection for air monitors?
How about that "Java" by Al Hirt at the end?

I've got to second everything Tom just said. Disappointment & Breakaway are two words you'll never see in the same sentence (except this sentence)