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Texar Audio Prism

A

ASchuelke

I always thought the processing that the AM radio station I grew up listening to and eventually worked at suited the format very well. It ran a Marti CLA-40 at the studio, and an Audio Prism (undoubtedly an AM version) at the transmitter. Nothing after it. So, I got my hands on a CLA-40 and an Audio Prism. The gentleman I bought the Prism from was kind enough to remove the "AM stuff" on it (limiting and clipping and filtering) because I'm running a web-only station.

The sound is CLOSE, but not really there. Some noticeable inconsistencies with level and spectral balance. Could it be that the "AM stuff" did that much to the audio, and by removing it, it just doesn't sound the same as I remember it on the AM station?

I'm sure I could hook up the AM portion of the Prism, but if I recall correctly, it's going to limit my bandwidth to around 10K. For those of you that are familiar with these units, is there a limiter/clipper that can be run AFTER the Prism that would work in the same fashion?

I'd certainly appreciate knowing what (if anything) I can do about this. I'm trying very hard to replicate that certain sound, and I thought it was almost guaranteed when I bought those units... but, I think having that "AM stuff" removed from the Prism is holding it back.
 
Keep in mind that depending on your streaming bitrate you may actually improve your sound by limiting what your encoder has to process. When I ran my stream I was running 64K and the processor I was using, an Optimod 6200 DAB, allowed me to reduce the bandwidth feeding the encoder. I eliminated all the high frequencies that weren't being sent across and it improved things dramatically. I'm sure somebody better versed in online streaming can give you better particulars depending on your bitrate.

I don't recall if the "AM stuff" as you put it, the Phoenix was the AM unit if I remember correctly, includes any NRSC pre-emph and filtering or not. This may have added to the sound along with any clipper that is on-board.
 
Bill DeFelice said:
I don't recall if the "AM stuff" as you put it, the Phoenix was the AM unit if I remember correctly, includes any NRSC pre-emph and filtering or not. This may have added to the sound along with any clipper that is on-board.
Click to expand...

I just saw one on ebay and I guess I was wrong, as the Eagle appears to be the AM version.
 
The Eagle is the AM version indeed. The one I have on the air isn't NRSC complient. I'm guessing all of them aren't. I have a Inovonics NRSC filter after the Eagle.
 
Bill DeFelice said:
Keep in mind that depending on your streaming bitrate you may actually improve your sound by limiting what your encoder has to process. When I ran my stream I was running 64K and the processor I was using, an Optimod 6200 DAB, allowed me to reduce the bandwidth feeding the encoder. I eliminated all the high frequencies that weren't being sent across and it improved things dramatically. I'm sure somebody better versed in online streaming can give you better particulars depending on your bitrate.

I don't recall if the "AM stuff" as you put it, the Phoenix was the AM unit if I remember correctly, includes any NRSC pre-emph and filtering or not. This may have added to the sound along with any clipper that is on-board.
Click to expand...

I run our station online stream at 32kbps (Primarily Talk) using an Aphex Compellor and a Dominator.

The Dominator does a good job of frequency shaping the high end. (I run the HF EQ all the way down and enhance the low end) This really smooths out the high frequency swishiness of the low bitrate encoding and provides consistent levels.

These boxes are available on Ebay for about 5-6 Hundred for a set.

You can listen to the WLOH stream at wm13.spacialnet.com/markbohach89061
It's not perfect but sounds a lot better than some.

Mark Bohach
WLOH
 
I have the board taken out of the am nrsc prism,it has 4 sub boards fitted on it,and this all fitted directly under the top cover.

The board is marked AMC-2,with the usual drive,asym and tilt controls.

I thought the phoenix was an am prism,so what is the difference between the phoenix and eagle ?

Somewhere i do have the manuals, but it's been a while now.

Paul.
 
BROADCAST said:
I thought the phoenix was an am prism,so what is the difference between the phoenix and eagle ?
Click to expand...

That's what I thought. Perhaps the Eagle got renamed when Gentner took over the product line?
 
@OKCRadioGuy: You're using the Inovonics for the filtering? So your AM version of the Prism doesn't have any roll-off or filtering? Interesting.
Maybe all I need to do is just hook the electronics back up that make this an AM Prism. I was under the impression that the Eagle/Phoenix portion of the Prism would roll-off the highs and make it sound very AM.
 
Bill,
The Phoenix is the gentner version of the eagle !
I have found the manual,the AMC-2 board is the aplitude modulation controller.

There is 2 main variants,AMC-1 (non NRSC) and AMC-2 (nrsc 1 compliant*).

The manual says there was 4 versions of the AMC-2, namely EBU, CUSTOM, NON NSC, and NRSC*.

On the AMC-2, the audio goes through pre-emp, limiter, and finally nrsc filter/clipper.
IIRC the clipper had a distortion controller,in that the clipped products were used to control the limiter before it so acting as an "intelligent distortion controller" kind of idea !
 
Thanks, Paul. I knew I was at a station that had a Phoenix but I was starting to doubt I saw what I remembered. Thanks for the clarification.
 
Regarding the comment about the filters making it sound "very much like AM:"

It's worth mentioning that AM broadcasts (up until the digital debacle) have, for about the past 25 years, sounded truly exceptional.

The problem has been the receivers. Manufacturers would make a $650 receiver, spend $649.51 on the FM portion, and 49 cents on the AM.

That's how you end up with AM receiver specs like Total Distortion: 3% and Response: 275 - 2800 Hz.

Most AM stations have been flat to the NRSC standard, 50 Hz to 9800 Hz, for about a quarter century. Unfortunately, the audience has rarely heard what is being broadcast due to the horrible receivers... yet, the FM sounds great, so it MUST be AM's problem...

If you're streaming in standard mp3 at 80 kbps or lower in stereo, as mentioned above, that 10 Khz rolloff could be a God-send. I think you would also be shocked to hear just how crisp a response to 10 Khz really is! (Most home cassette decks, for example, rarely produced anything over 11 Khz, and often a LOT less.)

I agree with this idea of giving it a try; I think you'll be pleasantly surprised!
 
The Phoenix does have a NRSC filter. It also has a cool distortion limiting clipper. They have a VCA driving the clipper and the its compared with the input via a biased comparator/integrator. If the clipping gets too deep, the VCA lowers its drive. There's a control that you can use to set the ultimate clip depth by varying the bias.

I ran a Prism/Phoenix in a cool way at 850 in Boston-I put a rebuilt BL40 Modulimiter in between the Prism part and the Phoenix clipper/filter (I also narrowed the bandwidth of the last three bands in the Prism, IIRC I crossed over between bands 2 and 3 at around 700 Hz and 3 and 4 at 2.5 kHz). I put a 600 ohm resistor on the transformer output and used the unbalanced monitor output to drive the clipper/filter. We ran a mono Compellor/Aphex combination at the studio in front of the microwave STL and ran the Audio Prism part as a fast AGC. It CRANKED! My replacement put on a 9100B Optimod-which in my opinion didn't sound near as good. Last I saw it was at 1510 in Boston (on their MW-50 standby).
 
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