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Orban Optimod 8500 Overshoots

This may be where our respective troubleshooting throughs may diverge here, but...

I'm concerned about you looking at one processor through one FM, and the other processor through a separate station. As it appears to me, you're assuming the Optimod is the culprit, but you're feeding it through the stereo generator of a completely different exciter.

Have you tried the Optimod on the station that doesn't overshoot?

The other thing is, I think you miss out on some of Optimod's processing features if you don't use its own stereo gen... especially in the area of overshoots and any composite clipping you might consider using. That was the major point of the processor/stereo generator combination that started the whole Optimod product line. Since it's right there, have you tried feeding the composite output of the Optimod to the exciter directly? That might narrow down the possibilities a bit.
 
I've watched the Optimod now overshoot on two different exciters, out of the exact same transmitter, using both the composite output, and the AES output. Yes, I believe it is the culprit. Regarding looking at the Omnia 11 FM, and the Optimod 8500, through the Inovonics 531, I have used the exact same 531 on each transmitters RF sample port, so it's not the 531 that has the problem. I really don't have much of a choice, when it comes to using the internal Optimod 8500 features, especially now that the Geocasting guys are in control of exactly what input and outputs they need, for their setup.
 
Brian Bowers said:
Just learned from the Geocasting guys that we are in fact using the 8500 AES output for the main exciter input. The composite is only connected for emergency switch-over purposes. Stereo pilot is being utilized in the Flexiva exciter, not in the 8500.

I probably couldn't explain everything there is to know about Maxxcasting, or Zonecasting, as I am, believe it or not, still in the dark on some of what is going on with that system. I think Geocasting's website could possibly explain it better than I could.
Click to expand...

I looked at the website. They site a case study station that is no longer even in the market. I can find no app for experimental authority to operate/test it.
Furthermore...it seems to imply there is a main signal and lots of PCS cellular style low power sites. I get the concept of boosters...fill in sites for areas the main site poorly covers...but the site seems to imply that each of these low power sites could have different commercial matter. I'm confused as to how a radio would choose the low power site if the main site has a higher signal strength and how these two would not create massive interference zones. It makes sense to me if there is NO main signal but not a main and twenty low power sites all within the main signal's city grade.
Can anyone explain?
 
Again, I don't know their system inside and out, but they use some sort of delay, from the main site, to the booster sites, using the AES feed. I'm not sure where the delay is inserted, but I'll tell you, the system performs very well. It is seemless, traveling from coverage area, to coverage area. One would think, with all of the transmitters on the same frequency, there would be delay, and phase problems, but there isn't, except, sometimes, for very weird tropo days, and even that is very rare.
 
Is comparing the Optimod 8500 even on the same level as an Omnia 11? One processor is in the $6500 price range and is not even the top of the line Optimod. The Omnia 11 is the top of the line Omnia box and cost $4k more $11K. It would make sense the Optimod can't control peaks and density as well as the 11. If it could, Orban would not have brought the 8600 to market. If your comparing the top of the line Omnia to an Orban, should it not be the top of the line Orban against the Omnia 11? You may have found the limit and reason for the Orban 8600 to come to market. Even the latest firmware may not bring the 8500 to the level of newer DSP technology in the 8600.

Is this Gecasting thing taking place on a tower in West Seattle by chance?
 
>>>Is this Gecasting thing taking place on a tower in West Seattle by chance?<<<

If it is, I know nothing about it.

>>>If your comparing the top of the line Omnia to an Orban, should it not be the top of the line Orban against the Omnia 11?<<<

Yes, if that was what I was trying to do, but that wasn't how I began the thread. Please re-read the initial post.
 
xmtrland said:
Is comparing the Optimod 8500 even on the same level as an Omnia 11? One processor is in the $6500 price range and is not even the top of the line Optimod. The Omnia 11 is the top of the line Omnia box and cost $4k more $11K. It would make sense the Optimod can't control peaks and density as well as the 11. If it could, Orban would not have brought the 8600 to market. If your comparing the top of the line Omnia to an Orban, should it not be the top of the line Orban against the Omnia 11? You may have found the limit and reason for the Orban 8600 to come to market. Even the latest firmware may not bring the 8500 to the level of newer DSP technology in the 8600.

Is this Gecasting thing taking place on a tower in West Seattle by chance?
Click to expand...

Clipping overshoots is quite easy and the technology has been here since dirt...almost. A couple of biased diodes, back to back, will create a brick wall. Will it sound good? No...that is why Orban first developed distortion cancelled clipping.
Every Orban product I've used, designed for on air, starting with the 8000, could control peak modulation with a combination of limiting and clipping.

No...there is something we're missing here. It all seems to have something to do with high freqs creating overshoots...Brian states that's the only time he sees the mod monitor light up. Too bad Bob Orban doesn't hang out on this list - he does on some others. I have to believe that something is not right here...either in the monitoring equipment, technique used to monitor, or in the 8600 itself.
 
I don't profess to know much about the magic inside Bob Orban's boxes, but the few problems I've had with them did revolve around the quality of peak limiting. The last Optiimod-AM I sent out to Bill and Kim Sacks was letting peaks get out to the point it was blowing a DX-10 off the air on regular occasions. After the box came back, you really understood what "brick wall" meant just by looking at the mod monitor.

Assuming for the moment that you don't really want to change the processor, I really think you should look someone up who's got service experience on it. For the moment, given its heritage, I'd bet the box didn't overshoot when it was new.
 
No knock on you Brian, nor am I trying so be Captain Obvious here, but there are a couple wildcards that need to be considered. There seems to be a level of uncertainty on how the program chain is connected, so I'm still hesitant to agree that the audio processor is not doing it's job correctly. Remember, (here comes the Captain Obvious part), everything in the chain is additive to the overall measured modulation level. For example; having a Nielsen encoder that sends out a watermark will increase the RMS level or for that matter, any other data (SCA) services stuck in the line. With high frequency peaks being the shortest in duration and potentially the highest dynamic range, when the overall level increases you'll see HF peaks move up accordingly. In other words, everything downstream of the processing also contributes to increasing your overall level. Some of these devices don't transmit full time either.

Another thing to consider is the way you're monitoring peaks. The Modulation Sciences box is probably twenty years old. Capacitors dry out and parameters shift. That monitor was somewhat controversial back in the 80's when it was new anyway, so without a way to benchmark it along side a known good 21st Century-style monitor like a new Belar, I would question it's accuracy.
 
If you look over the past posts, you'll see that I mention that the ModMinder is non-operational at this point. It arrived that way. Yes, when I initially received it, I did try hooking it up. It is currently at Lightner Electronics, to see if they can repair it. Even if it can be repaired (and I'm not even sure I'll have it repaired yet), I probably won't regard it as being the most accurate modulation monitor.

IMO, all audio ends up at the 8500. I would think, no matter what is inserted into it, it should be the brick wall limiter. Either it is not correctly working, or it was never capable of brick wall limiting. Don't get me wrong. I'm not trying to come down on Bob Orban and his Optimods. I personally love them, and their sound. I've used (and been a DJ with) the 8000, the 8100, the 8200, and the 8500. To my ears, they all sound(ed) musical, in an audiophile kind of way. All I'm asking is if anyone has noticed, or ever noticed, overshoots, when using the 8500. That's how this thread began.

I'd like to hear from other broadcast engineers, who are observing their modulation monitors. What mod monitor are you using. What audio processor are you using, and are you seeing any overshoots with it. I've gotta admit, I do like the affordably priced Inovonics 531 mod monitor. It seems to give me a good picture of what is going on, modulation wise. Either way, I doubt I'll get the 8500 repaired, if indeed it does need it. I have recommended that it be replaced with an Omnia 11 FM, next year.
 
Hi Brian... check to make sure there is no additional pre-emphasis turned on in the exciter if you are using the AES input.... also, some exciters have overshoot compensation that can actually ADD overshoot if misadjusted.

Mike Erickson
Wheatstone Corporation
 
Thanks for the suggestion Mike. This is a brand new GatesAir Flexiva exciter, and the previous Harris THE-1 (yes, we were still running one of those) did the same thing. Also, no on the double pre-emphasis. I can usually hear that right away, just like speakers being out of phase, when it is taking place.
 
The 8500 has energy beyond 16 kHz (nyquist) so it will overshoot on digital audio devices where the base sample rate is 32 kHz The Harris digit exciter had this problem with some processors as the base sample rate in the digital input module was 32 kHz. I'm not sure about the Gates Flexiva. I wouldn't trust any off-air mod monitor. Look at the RF sample from the transmitter itself. A composite input should have the peak tightest control if everything is working as designed.
 
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