Digital Audio Chain
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Thread: Digital Audio Chain

  1. #1

    Digital Audio Chain

    I'm very good with balanced analog audio, and know it very well, however, now, with a Voltair, PPM encoder, and sometimes a profanity delay, in the totally analog audio chain, en route to the transmitter audio processor, I'm wondering if there are a number of A-D and D-A conversions taking place in the Voltair, PPM encoder, and profanity delay, which now (cumulatively) degrade the final product. Our audio (that audio chain that I just mentioned), sometimes sounded different coming out of various exciters (using the exact same audio chain). There was a Continental 802B (dense sounding), a Harris MS-15 (amazingly clean), and now a Nautel 3.5 (producing the worst sounding audio of them all). I'm feeding a composite signal from the Omnia 11 into the Nautel. Before you all condemn me for doing that, also know that that is the way I fed the 802B and MS-15. We still have analog boards, so I don't, as of yet, have a digital signal to work with. I am wondering if I convert the console analog output, to digital (AES), and keep it digital throughout the audio chain I just mentioned above, if that will clean up my audio coming out of the Nautel. If I do that, do I have to watch out for clipping on the console A-D conversion, as we have some air talent that still peg the console meters? Any recommendations for a A-D converter to use, in this application?

  2. #2
    Quote Originally Posted by Brian Bowers View Post
    I'm very good with balanced analog audio, and know it very well, however, now, with a Voltair, PPM encoder, and sometimes a profanity delay, in the totally analog audio chain, en route to the transmitter audio processor, I'm wondering if there are a number of A-D and D-A conversions taking place in the Voltair, PPM encoder, and profanity delay, which now (cumulatively) degrade the final product. Our audio (that audio chain that I just mentioned), sometimes sounded different coming out of various exciters (using the exact same audio chain). There was a Continental 802B (dense sounding), a Harris MS-15 (amazingly clean), and now a Nautel 3.5 (producing the worst sounding audio of them all). I'm feeding a composite signal from the Omnia 11 into the Nautel. Before you all condemn me for doing that, also know that that is the way I fed the 802B and MS-15. We still have analog boards, so I don't, as of yet, have a digital signal to work with. I am wondering if I convert the console analog output, to digital (AES), and keep it digital throughout the audio chain I just mentioned above, if that will clean up my audio coming out of the Nautel. If I do that, do I have to watch out for clipping on the console A-D conversion, as we have some air talent that still peg the console meters? Any recommendations for a A-D converter to use, in this application?
    The Omnia 11 has a headphone jack. Does the audio sound OK there?
    I find it interesting that your best audio comes from a MS-15! A modern Nautel exciter should have pristine audio performance. A 802B, if in good operating condition, should not color the audio in that way.
    There is something not right with your audio chain. You also posted a while back that your Orban 8500 would not catch peak energy which is the first time I've ever heard someone have that issue. Do you have another engineering friend who could maybe look over your shoulder? Sometimes even the best tech/engineer misses the obvious...

    BTW...although some have a different opinion, I run analog composite into my Nautel. You may be able to measure the difference with lab grade equipment but I seriously doubt ANY listener would notice the difference. If your Nautel exciter has a digital multiplex input you might try that. Again...the difference can be measured but can listeners hear it?
    Last edited by wavo; 01-11-2017 at 05:04 PM.

  3. #3
    >>>The Omnia 11 has a headphone jack. Does the audio sound OK there?<<<

    Good question. I will check. This is mostly a part-time gig for me now, so I am only mostly there on the weekends.

    >>>I find it interesting that your best audio comes from a MS-15!<<<

    I know it, but it's true (IMO). Out of all the exciters that I have heard over my lifetime, I would have to say that that one MS-15 had the highest fidelity of them all (crazy, I know). When I was driving one day, while listening to the backup (which was using the MS-15), I couldn't believe what I was hearing. The highs were immaculate. We, however, are no longer using that exciter, as we now have the Nautel 3.5 (for the main), and a Harris PT4, (? I think that's the one) for a backup. Even though the Harris PT4 exciter looks like a Harris Digit, or Harris CD Digit, I think that I saw that it was marked SuperCiter. That's the first time I have ever seen or heard of that model. If you're wondering if the SuperCiter sounds different than the Nautel, I'll have to get back to you on that one, as I don't remember, but I am curious to find out.

    >>>A 802B, if in good operating condition, should not color the audio in that way.<<<

    One would think, but in my opinion, almost every exciter has it's own audio personality/signature.

    >>>You also posted a while back that your Orban 8500 would not catch peak energy<<<

    That is correct. That was me, however, that was/is for a totally different FM. That situation is on the back burner for now.

    >>>Do you have another engineering friend who could maybe look over your shoulder? Sometimes even the best tech/engineer misses the obvious...<<<

    I have several, but my situations and questions usually stump them, even though they are all seasoned veterans. Personally, I have a good 20-30 years of this stuff myself. I definitely don't mind picking people's brains though.

    I have also set up a selector monitoring system, where I can select a tuner (which can cleanly monitor the local competition), mod monitor output, or the transmitter audio processor input. As of yet, I have not connected the processor input audio to the selector switch. I plan to do that this weekend. That system is in place for the Nautel 3.5/Harris PT4 facility. The output of this system feeds some Dorrough Loudness meters, a decent external headphone amp, and a speaker amp.
    Last edited by Brian Bowers; 01-12-2017 at 09:43 AM.

  4. #4
    I'm noticing that the Harris SuperCiter is an analog only input exciter, but I also notice that the composite input is selectable between balanced and unbalanced. From the SuperCiter spec sheet:

    Wideband Composite Performance
    Input: Unbalanced, jumper selectable 50Ω or 10,000Ω (resistive), BNC
    jack or Balanced (jumper selected), 10,000Ω (resistive), XLR jack.

    I believe the Omnia composite outputs are also selectable (balanced/unbalanced). Maybe this is where my problem is. If one is set for balanced, and the other unbalanced, could this cause a difference in sound? I know that balanced analog audio is much better than unbalanced, especially in the broadcast world (with lots of RF nearby), is it the same for running balanced/unbalanced composite?

  5. #5
    I'm thinking that the unbalanced/balanced BNC composite has more to do with the length of the BNC cable being run, than the sometimes muddy audio that I am hearing. Balanced (composite) is better for long lengths, while unbalanced is better suited to shorter lengths. Anybody know if I'm right on that? When it comes to some of our audio sounding like bad MP3's, I don't think that it's related to the composite outputs that we're using. RDS and stereo pilot all seem to be fine. Modulation is perfect. I still think that this is a cumulative result of all of the A-D and D-A conversions taking place, en route to the audio processor.

  6. #6
    For those that are curious about the BNC composite connection issue, here are responses from Telos/Omnia, and Orban.

    Telos/Omnia:
    The composite output of all the Omnias (and most stereo generators) is unbalanced. And most exciter and STL inputs are unbalanced "bridging" inputs. I think some exciters have that option for hum elimination (ground loop issues) on long runs etc. Normally, just set it to unbalanced mode.

    Orban:
    The answer is in the proof-of-performance. Use whichever mode is the most quiet. If using a composite line over 100’ use RG6 and an isolation transformer if needed.

  7. #7
    Quote Originally Posted by Brian Bowers View Post
    I'm very good with balanced analog audio, and know it very well, however, now, with a Voltair, PPM encoder, and sometimes a profanity delay, in the totally analog audio chain, en route to the transmitter audio processor, I'm wondering if there are a number of A-D and D-A conversions taking place in the Voltair, PPM encoder, and profanity delay, which now (cumulatively) degrade the final product. Our audio (that audio chain that I just mentioned), sometimes sounded different coming out of various exciters (using the exact same audio chain). There was a Continental 802B (dense sounding),
    The 802B sounds dense due to excessive amounts if Intermodulation Distortion and noise they produce. Those exciters weren't very good to begin with.

    Quote Originally Posted by Brian Bowers View Post
    a Harris MS-15 (amazingly clean),
    By today's standards, those exciters are antique junk. In fact, they were junk back in the 80's when new. If you did a proof on either of those exciters, you would be amazed how bad they really are.
    Quote Originally Posted by Brian Bowers View Post
    and now a Nautel 3.5 (producing the worst sounding audio of them all). I'm feeding a composite signal from the Omnia 11 into the Nautel. Before you all condemn me for doing that, also know that that is the way I fed the 802B and MS-15. We still have analog boards, so I don't, as of yet, have a digital signal to work with. I am wondering if I convert the console analog output, to digital (AES), and keep it digital throughout the audio chain I just mentioned above, if that will clean up my audio coming out of the Nautel. If I do that, do I have to watch out for clipping on the console A-D conversion, as we have some air talent that still peg the console meters? Any recommendations for a A-D converter to use, in this application?
    Okay so you're probably not going to want to hear this Brian, but I'll try to be as kind as textual commentary can be.. First, I never want to discourage someone from getting into, or growing in the broadcast technical business, but sometimes we can get sucked into the Program Director or GM mentality of what "sounds good" or doesn't. Seasoned engineers learn over time that when the technical specifications and proper integration of equipment is correct, THAT is when you also get the best "sound". Modern gear will always function better than old gear, and swapping out exciters with old junk is not a sustainable methodology for reliable and consistent operation. In other words, taking the opportunity to make the signal chain as clean and simple as possible. That includes: paying attention to impedance of cables, noise sources that can bleed into gear or cabling, and above all; keep the program chain as SIMPLE as possible. Simple doesn't include daisy-chaining old gear with opamps and dried-up capacitors that contribute to cumulative distortion and noise to your signal.

  8. #8
    Kelly A, I couldn't agree with you more. I could hear the distortion on the 802B, I'm sure that's why it sounded dense and fat. I agree with you on the MS-15 too. I'm sure if I looked at, or listened to, the S/N, or listened closely for distortion, I'm sure it was there, but I'm not kidding, those highs were smooth as silk. That box was way past its time, so I'm glad we no longer have to rely on it.

    The investigation continues as to why the Nautel doesn't sound as clean as I think it should. I've audited and analyzed the entire chain, and connection wise, it is as clean as it can get. I simply have to keep in the EAS box, the Airtools 6100 profanity delay (we do bypass it when not needed), the Voltair, and the PPM encoder. There's no getting around those. The ultimate goal would be to have two routes from the on-air board, digital, and analog, and for quality comparison, simply switch back and forth. Then, one day when we get digital output boards, some of my work (and research) will already be done.

  9. #9
    I've found the Nautel exciters to be pretty good. Have you checked to see if the preemphasis on the exciter is turned on? Your audio processor is already outputting a preemphasized signal, so it would certainly make a difference if the exciter was to to as well.

  10. #10
    I'm not sure I'm understanding you correctly. I believe only one source should be the pre-emphasis provider - either the audio processor, or the exciter, not both. That's the way I've always understood it. I'm assuming that's what you're saying here too, yes?

    My hunch here is that the PD is sometimes uploading less than .wav files for the new music automation (NexGen) source. These then get A-D'd, and D-A'd a few times en route to the Omnia 11. The final picture (so to speak) is then not as clear as the original snapshot. I'm sure that there is currently at least one pre-emphasis source on. I doubt two, otherwise the air signal would be overly bright.

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