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Do radio stations still stack gear today?
- Thread starter 192khz
- Start date
What do you mean by "stack"? Are you referring to putting individual units, like audio processors, transmitter remote control units, various monitoring devices, the EAS receiver, telco gear, network related equipment and the like in a single equipment rack?
Hi 192khz-
Perhaps you have read or heard about audio processing "air chains" of the past. Back then a radio station might have processing gear occupying half a rack. Or even an entire rack, all for one mono audio channel. You can search right here on Radio Discussions and find threads about this.
This is because originally most rack mount devices provided one audio processing action. Over time, devices came to market that could do many audio processing actions in "one box" This happened in analog, and later in digital. Today's audio processors have many audio processing actions "stacked" in the device.
You might go to websites for the manufacturers and take a look at the documentation, which shows a block diagram.
192khz would you consider finding your way into a radio station or a content creation job where you can grow?
You are very interested in this, follow your interest and see where it takes you.
Perhaps you have read or heard about audio processing "air chains" of the past. Back then a radio station might have processing gear occupying half a rack. Or even an entire rack, all for one mono audio channel. You can search right here on Radio Discussions and find threads about this.
This is because originally most rack mount devices provided one audio processing action. Over time, devices came to market that could do many audio processing actions in "one box" This happened in analog, and later in digital. Today's audio processors have many audio processing actions "stacked" in the device.
You might go to websites for the manufacturers and take a look at the documentation, which shows a block diagram.
192khz would you consider finding your way into a radio station or a content creation job where you can grow?
You are very interested in this, follow your interest and see where it takes you.
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Yes. I’ve tried giving stations a call but no luck so far. I’ve explained i have experience with the omnia 9 processor (Omnia 9 PTN demo software).
My main setback is i’m 17, so I will have to wait til 4/20 to try to truly apply.
Like the analog days radio. Multiple processors.
In the world of digital processing that combines analog and HD out of one box, the answer is usually no. Of course there could be some old-school folks who stick analog processors with noisy VCA's ahead of their digital processor because they think it helps. What introducing cascading noise helps exactly? All perception, no reality.
Umm...well, it seems like we've done this one before.
"Noisy" VCAs in processors were never the problem. The dbx 165 from 1975 used the dbx 202 VCA and somehow ended up with an equivalent input noise figure of -90dBm. That's a "real" vca in there, and that box had performance that easily beat any recording or transmission (or receiving) device of it's day, and still does in may cases. The raw 202 had THD figures at .03% over a 40dB control range. You don't do that with a noisy VCA.
Aphex Compellors from later that same decade might seem "noisy" if you only read the specs (which were made without any stated bandwidth limiting filter, and unweighted), -67dBu might seem noisy. That's until you realize that the 15KHz band-limited noise was far lower, and with gain reduction, the noise floor went down too. Then you measure under real conditions and find it's really in the high 70dB range referenced to +4, with a total dynamic range of the box being in the mid 90dB area, similar to 16 bit PCM. That would have been the most common pre-processor for 20+ years. I also strongly doubt many stations could produce a mic noise floor 71dB below +4dBu out of a mic preamp, even today, being limited by noise in the room. And then you add mic processing.
Now, if you're thinking of the pre-VCA days, the Audimax days, or other products that didn't use a real VCA, then sure, they may have been noisy. But again, noise in the processing chain wasn't usually the problem, unless something went bad. Ever measure the noise floor of a vinyl record? Carts? Records dubbed to carts? Ever measure the dynamic range of today's music? I mean the music itself?
I don't in any way disagree that today's digital processors often don't require much if any pre-processing, and do include functions we used to have to do separately. In fact, they have for decades. And even if the odd situation comes up and you do need something before it in the chain, there are several digital solutions. But let's not just malign an old technology categorically as if it was universally awful. If you have one, a properly maintained and aligned Compellor will not degrade the noise floor of the received signal today.
But apparently, there are just enough sloppy board-ops and jocks in the world who don't even know what a VU meter looks like, and treat faders like on/off switches, that Mike Dosh at Angry Audio has seen the need for yet another pre-processor line. Yes, they're digital. I don't know for sure, but I strongly susupect the idea sprang from the fact that you can't buy a new Compellor.
My personal view- we are at a point in time where component failure in an aging Compellor is a factor to consider, especially since a Compellor may be a single point of failure in an audio chain.
Much respect for Marvin and Donn at Aphex for making an excellent product.
Much respect for Marvin and Donn at Aphex for making an excellent product.
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The problem has never been a single VCA device, but when you start stacking VCAs plus Opamps becomes the problem. Stacking devices in front of one another, usually a combination of VCA's and Opamps increases the summed noise floor logarithmically.
But that's the thing, forget the published specifications. Take a good quality audio measurement system of the day like a Potomac Instruments generator and analyzer, or an Audio Precision and measure the s/n of an audio chain of old that uses VCA stacked processing devices, versus even an older digital Optimod, like the 8200. The difference is quite obvious. Every dB of noise being generated by stacked devices is wasted modulation and adds to diminishing the overall listening experience. Of course, those who want to compress and clip the crap out of their audio chain to make it appear loud, don't care about things like listening experience other than their own skewed perception of what sounds good.
And also too, old Compellors are, well, old. Caps dry out and are rarely replaced until the piece of equipment fails, if at all.
If you were able to toss a new Compellor on the test gear and one that's thirty years old, of course, there will be a noticeable difference in noise and performance.
The quick and easy answer is, no - not usually. There really isn't a need to because modern processors, for instance, have the functions of what would have been at least a few separate pieces of equipment, now combined in 1 nice, tidy unit in the rack. In simplest terms, think of your smartphone. Back in the day you'd have a separate calculator, computer with internet access, a calendar, Rolodex, telephone, CD player and a host of other gear, to do what your phone, in the palm of your hand can do in 1 device. It's the same as mixing consoles for concerts. Back in the analog days, 20+ year ago you'd have the mixing desk which, depending on number of channels and other stuff, could be a behemoth, then you'd have outboard gear in the racks for compression, limiting, effects, EQ, patching and a whole host of other things. Now in the age of digital, all those ancillary racks full of equipment have gone away for the most part, because all the stuff that outboard gear was needed for, can now be done within the digital mixer itself.
BTW, I mean this with respect @192khz but is there a reason you seem to ask so many questions, specifically about processing? You've posted various threads asking about which model processors various stations in the Pittsburgh market use, how best to install/setup processing, you've mentioned in a few threads that you've played with an Omnia 9, and have also mentioned you've called various stations about their processing. With so many other things in the signal chain aside from the processor, is there a particular reason you take a specific and repeated interest in that?
Actually, if the two noise sources are random and of precisely equal level, they sum with a resulting increase of 3dB. IF they're equal. And they're usually not, the higher noise floor dominates, and the increase from it plus the second source is less that 3dB. In the case of the processors I cited that already have a total DR equal to 16 bit PCM, this is simply not a problem.
Noisy opamps hasn't been a problem for many decades now. We got the 5534 in the mid 1970s. In a 60dB mic preamp gain circuit equivalent input noise is -129dB...about 2dB off theoretical thermal noise. And that's perhaps the most common opamp in broadcast gear of the 1980s on, until we got the all that PMI/SSM stuff which nudged the noise floor down farther. There were some earlier noisey opamps, like the 709, 301, and (ugh...for audio??) 741. But those haven't been in audio gear for over 45 years, certainly not in the audio path of a processor.
This is a fairly pointless argument, as neither of us can prove it, and we're not throwing actual measurements into the mix. But I'll just disagree with "quite obvious" for now. The noise increase, related to processors, has to do with the increase in gain required to get them above threshold. If they're all set for unity gain, you won't notice any noise increase. So, we crank up the input to the pre processor so it's doing 10dB of GR. What happens when it releases? You now amplify whatever noise is coming in by 10dB. Do that again in the next processor...etc, etc. But it's not the processor itself, it's the noise in the system that's being amplified. You could tell by terminating the input to the first processor, vs connecting it to whatever you're driving it with. In those analog days we had noisey telco lines, analog STLs, and analog source gear. If you didn't pre-process before the biggest noise maker (lets say, an analog STL), you'll be amping up its noise at the TX end. A lot. Again, not strictly the processor at fault.
What's changed is the system. We have digital systems end to end. That means we now have complete knowlege and control of where 0dBFS is, and how much DR we have below that. But, we still have to be careful with the above situation. If we're sliging 16 bit audio around, we "only" have 96dB, and really, more like 93dB of DR. If we allow 15 for headroom in the system (before processing), our noise floor is now "only" down 78dB from average signal. Now you go into a processor with that, and push it to 10dB of GR. And then let it fully release. Now your noise floor is 68dB and everything is working just fine, nothing's broken, nothing has "noisey VCAs" or "noisey opamps".
Now before we got saying "yeah, but I run 24 bit audio", yeah, no you don't. You have 24 bit words. Your actual audio is 20 bits of DR (because ADCs can't do noise floors lower than thermal noise), and your source devices are more than likely 16 bits, probably compressed. And then there's the mic, preamp, and the elephant in the room...the room. And we're right back to where we were.
I need to clarify here. I'm not taking ANY issue with the need and goal of low noise. Not at all. Low noise is good. But your sentence above isn't making sense. Lets say you somehow manage a noise floor at 78dB below 100%. And then you add another 3dB of noise, to put it at 75dB. What modulation has that wasted? Your -78dB was 0.0125% mod. You've bumped that up to a whopping 0.0175% "wasting" an additional 0.005% of your total mod. Pick your noise levels, run the calculations, it never wastes even 0.1% of modulation. Diminish the listener experience? The average acoustic noise level in a quiet living room is 30dB SPL. To hear the -75 noise floor above that, they have to play your station at 105dB SPL, which is darned loud. While possible, there are few formats that would be tollerable that loud for very long. And that assumes they could actually receive your -75dB noise floor (which they can't). Car listeners? Nope. The average interior noise in a car is between 60 and 70dB SPL, covering any broadcast noise you may have quite well.
You are literally "amplifying" the "noise issue".
I will say, just so everyone knows I DO care about noise, I spend many years working for a station where noise mattered. A lot. The transmitted noise floor could be as low as 82dB below 100%, that's until a source was played, even a digital one. We found that nothing on earth could receive that low a noise floor. Nothing. Low 70s in practical receive situations. There's one thing HD Radio improved on.
Different issue. We can discuss, but there's literally no point right now.
All true, and I've never (hopefully!) implied that anyone should just toss an old piece of gear into the air chain. But...funny...I've had the opportunity to pop the top on several Compellors lately. None new, of course, and yes a couple were in their 30s. They'd been sitting for years, unpowered. My goal was to rehab them then find them a new owner. The first step, after making sure nothing is smoking, is to run some audio tests. You are correct, there was a noticable difference between their noise performance and the original specs. They were better! Yeah, better. No power supply ripple, no hiss, boom rattle, nothing unusual other than to beat their published specs. That doesn't mean they didn't get recapped a bit, because hey, fair is fair. But it does say a lot about how Aphex designed stuff. And the new caps didn't improve anything. I had a dirty pot and a couple of dirty contacts to clean.
I did mention the Audio Chameleon, right? There's your "new Compellor". Well, not exactly. Probably much better, but I haven't tried one personally.
Ran sum numbers (because I was curious). All noise figures are calculated with a 20kHz bandwidth, and are unweighted. The circuit is a typical non-inverting 20dB gain configuration with a 10K feedback resistor and a 1K from the inverting input to ground, temp is 20 degrees C, power suppply is +/-15V. Total noise includes the opamp and resistors.
5534 has a total dynamic range of 116dB.
A TLO72 has a total dynamic range of 108dB.
The data on the much older LM301 is not very complete, but it looks to be about at the same noise level as the TLO72, though other specs are worse. I couldn't find enough data on an LM709.
The absolute quietest IC opamp today, the LT1115, in the above circuit and conditions will get to 119dB DR.
These numbers are for one opamp, and obviously even two in a differential circuit will raise the noise 3dB.
But you might begin to see why true 24 bit noise levels (144dB) are total mythology outside of the digital domain. And sooner or later, we have to work outside of the digital domain to get signals in and out of it.
5534 has a total dynamic range of 116dB.
A TLO72 has a total dynamic range of 108dB.
The data on the much older LM301 is not very complete, but it looks to be about at the same noise level as the TLO72, though other specs are worse. I couldn't find enough data on an LM709.
The absolute quietest IC opamp today, the LT1115, in the above circuit and conditions will get to 119dB DR.
These numbers are for one opamp, and obviously even two in a differential circuit will raise the noise 3dB.
But you might begin to see why true 24 bit noise levels (144dB) are total mythology outside of the digital domain. And sooner or later, we have to work outside of the digital domain to get signals in and out of it.
Is some way of determining internal headroom in digital signal processing a good idea?
Should digital consoles and audio processors have an internal gain structure dashboard visible in the GUI?
Should digital consoles and audio processors have an internal gain structure dashboard visible in the GUI?
Interface digital maximum (in/out) is always set at 0dBFS at the ADC and DAC (in practice, somewhat less because of intersample overs). Internal (DSP) dynamic range of processors and consoles is set by bit depth, which is, these days, 32 bit or 64 bit floating point math. 32 bits linear quantization has a 192dB DR, but then they use a few bits for floating-point math, essentially a dynamic "gain set", and the DR becomes 1528dB for 32 bit fp, and effectively removes the concepts of "dynamic range" and "gain structure" from the discussion completely, even taking 0dBFS out of the internal picture. The issues are all placed at the inputs and outputs, which if digital, are limited by the bit depth and 0dBFS, and if analog, are limited by the analog noise and 0dBFS analog level, usually well under 115dB. Thus, console and processors internal gain structure is no longer relevant, other than the nonlinear effects of the dynamics processing itself which is extremely algorithm dependant.
Older digital consoles and processors did not use floating-point math, so were limited in DR by their internal DSP bit depth. Gain structure would have definitely mattered in those, but at a practical minimum since the 1990s, would have been 24 bits, or 144dB, and is still very much limited limited by the analog interface, which we all used back then.
In the old days as well as today, the total system DR is limited by the source DR, with studio and mics being the worst, both because of residual and studio noise, and pauses that would expose it. Today, all common release and distribution data formats are 16 bits (24 bit releases are not "real" 24 bit DR) and studios, mics, and preamps are no quieter, being limited by dollars and physics. It doesn't matter, no analog radio listener can receive even close to a 96dB DR, and no listener, analog or digital, can reproduce a 96dB DR at their end. Nor would they want to.
Older digital consoles and processors did not use floating-point math, so were limited in DR by their internal DSP bit depth. Gain structure would have definitely mattered in those, but at a practical minimum since the 1990s, would have been 24 bits, or 144dB, and is still very much limited limited by the analog interface, which we all used back then.
In the old days as well as today, the total system DR is limited by the source DR, with studio and mics being the worst, both because of residual and studio noise, and pauses that would expose it. Today, all common release and distribution data formats are 16 bits (24 bit releases are not "real" 24 bit DR) and studios, mics, and preamps are no quieter, being limited by dollars and physics. It doesn't matter, no analog radio listener can receive even close to a 96dB DR, and no listener, analog or digital, can reproduce a 96dB DR at their end. Nor would they want to.