Just need to vent a little. Ticks me off how AM radios today sound like shit, if they are even lucky enough to pick up stations that are more than 500 feet away It's almost like AM built into radios today is an afterthought on the manufacture part.
Anyways I learned the hard way today that modulation monitors don't always help as well as you'd think! I can get the audio sounding perfect through a nice clean modulation monitor into a set of headphones. I can make it sound as good, if not better in some ways than an FM monaural broadcast. I can A/B between the modulation monitor and my input source and not tell any difference when not using processing which proves to me that my transmitter is not coloring the sound in any way (the o-scope also confirms this). Problem is it doesn't seem to matter with todays radios. What seems to sound great on one radio sounds like shit on another.
I do know a thing or two about audio processing for the AM "Medium Wave" broadcast band. The problem seems to be the inconsistencies in every radio I find. With the FM band this doesn't seem to be a problem at all, it's damn near plug and play with FM gear. I swear to God with AM all the work goes into processing the audio and getting the antenna as efficient as possible.
So brainstorm here, is there something I am missing? I do know about the NRSC filtering that is expected with newer radios designed mostly for talk radio reproduction, but that doesn't seem to be the issue.
Do I just go listen to every radio until I get it sounding great on all of them? Or is there some magical recipe I am missing out on?
Like I said I am mostly venting, but if you have any ideas feel free to discuss them.
Post by Ozone Express Radio on Nov 19, 2011 20:01:07 GMT -6
This isn't a surprise, and honestly my experience with any MW broadcasting isn't even worth mentioning as my learning curve has been both steep and expensive.......So, I will just commiserate a bit.
When I say its no surprise, I mean that because every radio I've laid my hands on in the last 10 years has been a crapshoot at best, even more so on the AM band. AM is really an afterthought for radio manufacturers and as such I think they put as little money into it as possible. Other than talk, no one expects much out of AM, if they even listen to it at all. Ask anyone under the age of 40 about AM, and you are likely to get a blank stare if they aren't a DX'er or enthusiast. Add to that the sheer amount of awful and intolerable interference, and IBOC smudging everything into an unlistenable mess, and you have a recipe for disaster.
Of the pile of radios have around here, the only ones that actually have AM tuners that are consistent and listenable are generally the ones with tubes in them, save for a GE Superadio, a Grundig and one very old Realistic unit from the very early 70's.
Just need to vent a little. Ticks me off how AM radios today sound like shit, if they are even lucky enough to pick up stations that are more than 500 feet away It's almost like AM built into radios today is an afterthought on the manufacture part.
AM radio is lucky to even still be included as an afterthought.
Anyways I learned the hard way today that modulation monitors don't always help as well as you'd think! I can get the audio sounding perfect through a nice clean modulation monitor into a set of headphones. I can make it sound as good, if not better in some ways than an FM monaural broadcast. I can A/B between the modulation monitor and my input source and not tell any difference when not using processing which proves to me that my transmitter is not coloring the sound in any way (the o-scope also confirms this). Problem is it doesn't seem to matter with todays radios. What seems to sound great on one radio sounds like shit on another.
Trust me, you are going to want to trust that modulation monitor and the sound quality from it, as well as the scope measurements as your baseline reference in how your station is sounding. Never rely on ANY standard radio receiver for proofing!!!
I do know a thing or two about audio processing for the AM "Medium Wave" broadcast band. The problem seems to be the inconsistencies in every radio I find. With the FM band this doesn't seem to be a problem at all, it's damn near plug and play with FM gear.
The reason is because the conditioning for FM vs AM happened a long time ago and then even more so after the foul up with AM Stereo standards during the 80's. Had it been done right, AM truly would have had an unstoppable comeback.
I swear to God with AM all the work goes into processing the audio and getting the antenna as efficient as possible.
Once you have that sound quality as good as you have had it listening via the modulation monitor, all the work then should be focused on the antenna efficiency. Trying to get that uniform audio sound from a variety of radios where they are barely capable of receiving full NRSC characteristics much less a standard all would follow for bandwidth response specs, will only result in wasted time and a lot of frustration.
So brainstorm here, is there something I am missing? I do know about the NRSC filtering that is expected with newer radios designed mostly for talk radio reproduction, but that doesn't seem to be the issue.
The issue is that the manufacturers cut many corners and despite the NRSC filtering specs, 99.999 percent of radios are made overseas where tolerances from one make to another in mass production will not follow within any standard minimums to each other, hence your experience in hearing all those varieties in sound reproduction from those different radios.
Do I just go listen to every radio until I get it sounding great on all of them? Or is there some magical recipe I am missing out on? Like I said I am mostly venting, but if you have any ideas feel free to discuss them.
I would trust what your hearing out of the modulation monitor and feed that into your studio monitor system and forget about how all the radios are sounding different. It's not your station or your processing, its all those different radios.
Peace!
K-ROCKS RadioOne
ZeroPointRadio
AM Stereo 1670
FM Stereo 92.1
After some screwing around with EQing, compression, hair pulling, and listening directly to the modulation monitor and the best widest IF band radio I could find I think I am finally happy.
I know what should sound good on the modulation monitor should be taken as truth, but I find there is a tiny bit of compromise to be had to make your *average* radio sound that much better.
It didn't help I was compressing the audio after I applied the NRSC equalization which made issues even more complicated since the obvious high frequency audio intensification would screw with the lows making for some music sounding perfect and other stuff sounding terrible.
Well it's a fun educational hobby after all, we all make mistakes. Just seems like with AM it's way too easy to assume something on paper should sound good in real life.
I still am running the EQ for the high band compression adjusted for NRSC, but I compensated for it by readjusting the middle audio frequency range. The low bass band compression is EQed and compressed for maximum punch without noticeable breathing with kick drums and such. (not to confuse, but I am running two bands of compression, one for the low bass end, and the other for medium-high end, combined at output and then into TX)
Finally after comparing my station to a few others on the dial which I consider to have professional high grade processing, I can't honestly tell much of a difference!
Sure there are a few quirks and the audio lacks in some places, but overall I am impressed now. It really is amazing switching the audio processing in/out of the chain. Running pure audio sounds like shit lol, I mean compared to all the other stations running a rack full of equipment to get the most bang for their buck in audio.
I guess the only place to go from here would be building some kind of circuit to make for more asymmetrical audio, upgrading from my goofy two band compressor to a more professional 3 or more band compressor. But hell at a point I think there is only diminishing returns. I mean it's only 10 watts of power into a 30 foot T antenna, not like I am running a kilowatt legal AMer Your average listener probably wouldn't even care, but the goal is to make them not want to tune out after all.
I suppose I should be happy that the audio sounds as good as mono FM from my modulation monitor, and that I can get this far with such little equipment.
If I sound like the other stations on the AM dial using most radios, even those with good audio fidelity, then I should be happy right? Heh.
Now if I can just convince people to listen to AM radio again rather than FM or their IPODs Oh well at least I can broadcast to myself and that one lonely guy out there on the road with only an old GM car radio ;D
Oh I should mention that the TX I built can tune up to 3.5Mc if I wanted using an external VFO or XTAL oscillator. So who knows maybe one day if I get bored with local MW broadcasting I could tune up to 90 meters shortwave and do some shows. I am sure my "T" antenna would work wonders on that band. I remember listening to The Crystal Ship doing broadcasts on that band and got out well with low power. I'd have to cut the audio bandwidth back to 5KHz though I think correct?
I guess the only place to go from here would be building some kind of circuit to make for more asymmetrical audio, upgrading from my goofy two band compressor to a more professional 3 or more band compressor.
I guess the only place to go from here would be building some kind of circuit to make for more asymmetrical audio, upgrading from my goofy two band compressor to a more professional 3 or more band compressor.
It works incredibly well and IMO...better than what the over rated 222 can do in C-QUAM mode.
Peace!
Hey thanks for the link! You read my mind, I was going to ask if anyone knew of a good schematic for such a circuit. When I get the parts and time I may attempt building it
I swapped a major section of my modulator out for a better design. No need to go into details but will just say the low end really comes through clear now right down to 20Hz with almost no distortion on the scope. I can practically bring the thing to DC levels on modulation.
Series modulation really kicks butt for fidelity but I notice one odd characteristic on the modulated carrier waveform. When the modulation drags the carrier to its maximum negative peak without distortion it looks like the sine wave I am testing it with gets squished slightly at the negative end. Almost looks like the negative peaks gets slightly compressed just by the series modulator itself and I'm not talking about full cutoff or distortion. From lots of research I think I come to the conclusion that this is somewhat normal with series modulation and is actually a good thing as it takes more force to push negative cutoffs which in turn helps reduce distortion on large peaks. Sort of asymmetrical in a way.
Just for fun I whipped together a quick crystal radio set and plugged its audio into a good stereo system that also had another input taken from the direct studio audio. I A/B the two and was amazed at how identical they sound. I really couldn't tell any difference apart from the studio feed and the over-the-air audio until I switched in my audio processing, which obviously made it sound even better!
Now it's time to search for the best high fidelity AM receiver I can find for a studio monitor. Yes I know I could just use a basic diode detector, but I really want to find a good receiver, partly because I want to also hear other stations on the air in HIFI and see how good they sound.
My DX398 has a tight filter on it which is nice for what it does but useless for listening to wideband AM music stations. I also have a C. Crane SW pocket radio that has a more open end but lacks the bass. The only half decent wideband HIFI AM radio we have here is a Phillips stereo but even that isn't as opened up as I would like.
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