Optimod-AM 9400 manual

[westlife]

> Not trying to belabor the discussion, but I just checked the
> NRSC websight, and do not see where preemphasis is mandatory
> for AM-Stereo. What reference are you basing this on?

Look in section 73.128 of the FCC rules. Specifically, 73.128.c:

<PRE> (c) Effective on December 20, 1994, stereophonic transmissions shall
conform to the following additional modulation characteristics:
(1) The audio response of the main (L+R) channel shall conform to
the requirements of the ANSI/EIA-549-1988, NRSC-1 AM Preemphasis/
Deemphasis and Broadcast Transmission Bandwidth Specifications (NRSC-1).
(2) The left and right channel audio signals shall conform to
frequency response limitations dictated by ANSI/EIA-549-1988.
</PRE>
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<a target="_blank" href=http://www.cgl.uwaterloo.ca/~csk/its.html>Be kind to your friend, the apostrophe.</a></P>

 

[rorban]

The DSP in the Optimod 9200 is now decade-old technology, and even though the latest software for it is very good, the 9200 has earned a reputation as having a cold "digital" sound, much like the Optimod-FM 8200. If Orban wants to convince enough existing 9100 owners to install a new 9400, they will need to make it clear whether or not the 9400 is based upon all new DSP technology, or if it's still using the same 10-year-old design as the 9200, just doubled to make it stereo. Because if that's the case (old DSP in a new box) then I don't think many stations will be hauling their old 9100s off to the dumpster just yet!

The 9200 was built on the 8200 code base. The 9400 AM processing is built on the 8400 v3 code base. In both products, there were very substantial DSP modifications to adapt the algorithms to the requirements of AM analog transmission through radios with a typical audio abndwidth of 2.5 kHz.Compared to the 9200, the 9400 adds "intelligent" clipping distortion control, more versatile equalization, anti-aliased clippers, stereo processing, and a speech/music detector that allows the user to separately optimize the processing for speech and "non-speech" program material.The 9400 also introduces parametric lowpass filters, allowing the user to set not only the cutoff frequency of the processing, but also the shape of the transition region. This allows a tradeoff of filter ringing against high frequency extension. This is particularly useful for stations who have reduced bandwidth to 5 kHz for HD and stations outside North America that have always been required to broadcast with limited bandwidthExcept for the stereo enhancer and AGC, the AM and digital radio processing chains in the 9400 are entirely independent, with two equalizers, 5-band compressor/limiters, and peak limiting sections.Although the AM analog processing chain presets purposely have the same names as the presets in the 9200, these presets are entirely new and have been tuned by Greg Ogonowski and me to fully exploit the 9400's more powerful signal processing. Additionally, there are a large number of digital radio processing presets specific to the digital radio chain. These can be "mixed and matched" with analog AM presets. Bob Orban

 

[WGTO]

For those who do not know, I am an engineer owner, and being the big cheese at little WGTO I can play all I want with my rack full of processing goodies such as volumax, optimod 9100, omina ex5 inovonics 222 , crl 450 and even a 9200. Looking at real world car and table radios I find that either they are too brick wall to show any improvement with the pre-emphasis or else they respond with some nasty artifacts if we try to force feed them anything with much boost above 3.5 k.
Those radios that are wide due to lack of tight I.F. or are still well made enough to have a nice I.F. pass with decent rejection sound pretty good when processing is in the flat mode. Or maybe just a pinch of boost. By a pinch I mean maybe 5 db tops. I now bounce between my 9200 and the omnia 5 but run each one pretty flat and enjoy a much cleaner sound at the speaker where it counts. The distortion that comes from these tight no slope radios is best described as an edgy buzz or rough sound that kinda grates at you over time. Killing the heavy pre-emphasis rather than cutting the transmitted audio to 5 k seems to have a more pleasant effect. These radios seem to tolerate the high frequency as long as it not boosted. And the wider band radios don't need the boost as long as they are getting the full 10 kHz audio at the front end. So I just leave it flat. The overall sound is louder cleaner and reminds me more of the hey day of AM, nice and full. Like I said Bob was amazing when he came up with that super pre-emphasis for the radios popular in the day of the 9000 when most radios had a gentle roll off off slope from the I.F. that would allow some improvement with the boost. But today's junk and cliff edge I.F. slopes just can't handle it! And since these radios are still the most popular, we have to live with what they offer and they seem to demand almost flat audio to sound decent. By the way I think the best overall sound is my 9100b2 with a slight boost but alas my unit is getting old and is in serious need of new caps so the audio is getting a bit thin and I no longer use it . I will send it out for work when the budget allows!

 

[Smiths and Smittys]

Ding Ding Ding Ding...we have a winner...
Reviving a 6 year old thread!

 

[satech]

Ding Ding Ding Ding...we have a winner...
Reviving a 6 year old thread!

Indeed! I did a double-take when I saw the dates!

But to address WGTO, if you can't run NRSC pre-emphasis without getting objectionable distortion in receivers, then something is wrong with your transmitter or antenna system. The NRSC curve is actually very mild compared to the extreme amounts of high-end boost many AM stations were using as soon as multi-band processing allowed them to get away with it in the '70s.

 

[WNTIRadio]

Plus most receivers have de-emphasis on the AM side as well, so depending upon where you place your break point for the pre-emphasis, it could sound pretty dull. NRSC is up about 3dB at 2.5kHz. 5dB at 3kHz, and 7dB at 4kHz. Assuming your receiver rolls off starting around 3kHz and isn't a brick wall, but rolls off from 3-4.5kHz and even further, and has de-emphasis, it's going to sound pretty muffled.

The wide band radios have a 75us de-emphasis as per the AMAX standard if they were made in the last 20 years. Of course, there are very few of them.

I can hear the difference on my car radio if I turn off the NRSC, as well as most other receivers I have.