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Author Topic: IAS Intermod Specs  (Read 621 times)

Mark Hannah

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IAS Intermod Specs
« on: November 07, 2017, 12:29:10 pm »

Two parts:

1) How does one figure out the IMD specifications to use in IAS, WSM, WWB, etc?  Should a manufacture freely share the information?  I will assume that adjusting the original settings requires a level of experience that I don't have yet.

2) Because the shop I work for is 95% Sennheiser, I tend to go to WSM's professional mode most of the time.  I'll use IAS along side WSM for atypical gigs.  Since IAS does not factor an imported trace's amplitude for coordination, without spending time adding to the "active spectrum" list, I'll probably stick with WSM for most situations.

One of those atypical gigs is coming up where I'll be adding 6 Lectrosonics UH400a (Block 22, 100k spacing) to the mix. 

I've attached both IAS and WSM dialog boxes and would appreciate someone checking them.
     - Is there a reason by the numbers in IAS are not rounded up? 
     - IAS doesn't have a 3Tx IM5 option so what should I put into WSM?

Thank you in advance for sharing your knowledge!
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Pete Erskine

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Re: IAS Intermod Specs
« Reply #1 on: November 07, 2017, 07:48:27 pm »

Two parts:

1) How does one figure out the IMD specifications to use in IAS, WSM, WWB, etc?  Should a manufacture freely share the information?  I will assume that adjusting the original settings requires a level of experience that I don't have yet.


The formulas are theoretically the same however there is always a random component in the calculations to encourage the most results given repeated runs of the calculations.  The levels or allowable distance from each result is different for each program as well.  Don't waste time trying to get one program to agree with another.  Actually =the results are all good between all the programs, workbench included.

Watch a video I did comparing workbench with IAS.  In it I discuss how I tried to match the specs between the programs.  Mostly it was a comparison in doing the same wireless with the 2 different programs.

the videos are at the bottom of the page http://www.bestaudio.com/spectrum-scans/
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Mark Hannah

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Re: IAS Intermod Specs
« Reply #2 on: November 08, 2017, 05:45:27 am »

Pete,

If I'm running 40 channels of Sennheiser devices and adding 6 of another brand, then I'm better off using WSM so I don't have to manually type in frequencies.

Consequently, the desire to have confirmation that I copied over the numbers from IAS into WSM correctly.  And on how to get those numbers in the future for devices that might not be in IAS's database.

It has been a while since I watched your videos so I'll take another look.

Thank you.

PS.  I knew before purchasing IAS to not waste time getting two separate IMD programs to agree with each other.

The formulas are theoretically the same however there is always a random component in the calculations to encourage the most results given repeated runs of the calculations.  The levels or allowable distance from each result is different for each program as well.  Don't waste time trying to get one program to agree with another.  Actually =the results are all good between all the programs, workbench included.
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Dan Mortensen

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Re: IAS Intermod Specs
« Reply #3 on: November 10, 2017, 04:23:50 pm »


 How does one figure out the IMD specifications to use in IAS, WSM, WWB, etc?  Should a manufacture freely share the information?  I will assume that adjusting the original settings requires a level of experience that I don't have yet.


This is exactly the problem I'm having with my JTS microphones. I spent at least an hour in the Shure booth with Tim Vear at the NY AES convention learning about setting up WWB, which was hugely enlightening. We got most of the way through it, but the intermod specs for 2 and 3 transmitters came up, and that information wasn't in the JTS reply to previous questions.

The local rep has been helpful in asking both the manufacturer and importer, and I have asked separately, too, but info is not yet forthcoming. I have faith, though...

I looked up intermod calculations, and it seems quite

straightforward

as long as you know the frequencies of specific transmitters, but the the data entered in the data box must have more to it than just that, since it is a variable rather than a fixed calculation (meaning the intermods will be different as the frequency spacing of the transmitters is different, but the data box only contains some kind of spacing minimum, as near as I can tell). What is that difference and how is it calculated? Is that even the right wording for the question?

PS Pete, I watched your video comparing WWB to IAS and didn't see (or comprehend, most likely) what part of it would be relevant to this exact question. It was helpful otherwise in seeing how different programs made different settings easier or harder, among other things.

Also TIA.
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Dan Mortensen

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Re: IAS Intermod Specs
« Reply #4 on: November 22, 2017, 08:32:20 pm »

....the data box (of WWB) only contains some kind of spacing minimum, as near as I can tell). What is that difference and how is it calculated? Is that even the right wording for the question?

So as to not leave that question hanging, I spent some hours (yesterday and over the past couple weeks since posting it) with RF Explorer and Vantage trying to watch what the microphones do in use.

The first picture [with "1)" in the title] is the background RF in my shop. I chose the region that looks pretty flat in the high 400's, and set one mic for 496.325MHz. (Picture 2)

Looking in the Group Chart that comes with the microphones, I found one that had 496.325 in it, and the closest frequency above it that they recommend is 498.375MHz, so that was the second mic (Picture 3, with the first mic turned off).

That spike at 511.875 definitely was a result of Mic 2 being on, since Mic 1 didn't have a similar spike, so I noted its amplitude and frequency in case one of you looks at it and recognizes a problem. (Picture 4)

The calculator that I referenced above predicted the following IMD for those two frequencies. (Picture 5)

Turning on Mic 1 along with Mic 2 gave Picture 6, and the resulting spikes are exactly at the predicted frequencies, which was confirmed with a bunch of measurements (in similar pictures) I won't post here unless you want to see them.

It was interesting that Mic 2's 511.875 spike diminished as a result of having Mic 1 on. Any ideas why that would be?

There's a 7 picture limit per post so I'll go to the 3rd Order pictures in the next post. The final three pics should be together.
« Last Edit: November 22, 2017, 08:34:36 pm by Dan Mortensen »
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Dan Mortensen

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Re: IAS Intermod Specs
« Reply #5 on: November 22, 2017, 08:50:02 pm »

Zooming in on the lower 3rd Order harmonic (Picture 7) shows that it is spang on the predicted frequency, and it has an amplitude of roughly -43.5 dbm. "Roughly" because, as you undoubtedly know but I'm discovering, the values jump around with each pass of the scanner. I'm using variously the 5 scan to 10 scan average for Exporting from Vantage, but I think the displayed value may not show the average but only the last scan. Is this true?

Is there a way to get csv files displayed to show a cool graph like these screen grabs? The only way I've found is in WWB, and that screen doesn't show as much detail as this one. (There may be another WWB screen somewhere in there but I am not conversant with it yet.)

From these graphs I'm assuming the answer to my earlier question about the meaning of the bandwidth value in the 3rd Order box in WWB is the width of this spike, with some level down on each side of the peak being the proper value to set the lower and upper boundaries. Yes?

I grabbed what seemed like likely spots on each side of the peak (Pictures 8 and 9), but don't know if they are too much or too little. I'm guessing too much (wider than they need to be) because the bandwidth is so large compared to what was already in the box in WWB.

What values (how far down from the peak) are actually used for this calculation?

I haven't yet done the 3 TX research.

Am I on the right track?

BTW, JTS has still not given me the necessary information that would negate the need to do all this. They have sent a bunch of documents and data but nothing relevant to this exact part of the prediction preparation process.

TIA, and hope you all have/had a Happy Thanksgiving.
« Last Edit: November 22, 2017, 09:03:05 pm by Dan Mortensen »
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Mark Hannah

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Re: IAS Intermod Specs
« Reply #6 on: November 23, 2017, 04:03:28 pm »

After re-reading my OP and the responses, perhaps I should have only posted the two images and then asked...

1) Why give different devices different "spacing" parameters?  Tolerances of the product?
2) How are the "spacing" parameters taken into consideration when calculating IMD?
3) How do you figure out the "spacing" parameters for devices?

Mr. Mortensen,

I hope you didn't do all that work just for me.  Thank you.
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Pete Erskine

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Re: IAS Intermod Specs
« Reply #7 on: November 23, 2017, 10:12:04 pm »

After re-reading my OP and the responses, perhaps I should have only posted the two images and then asked...

1) Why give different devices different "spacing" parameters?  Tolerances of the product?
2) How are the "spacing" parameters taken into consideration when calculating IMD?
3) How do you figure out the "spacing" parameters for devices?

Mr. Mortensen,

I hope you didn't do all that work just for me.  Thank you.

All of these questions can be answered by... it's personal preferences.  Each software writer determines what kind of spacing is appropriate for each intermod...What works best for each piece of equipment.  I am sure there are tests to quantify the numbers but in reality it's up to you.

I tend to adjust the basic spacing depending on what I am coordinating.

After the IM is calculated all spacing is checked to insure that new frequencies stay at least the specified distance away.

In my video I set all the spacing the same between IAS and WWB for the test and the numbers came out vastly different.  There is no one way to calculate IM.  Each works well within the parameters of it's program.
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Pete Erskine
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Dan Mortensen

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Re: IAS Intermod Specs
« Reply #8 on: November 25, 2017, 08:12:21 pm »

Mr. Mortensen,

I hope you didn't do all that work just for me.  Thank you.

Hi Mark,

For you specifically, no; for me to learn what the bandwidth of an intermod spike is and what intermods are and look like, yes. And since your thread is about intermods and I'd previously expressed mystification about them in ITT, I thought/hoped it would be the right place to post it and share with anyone who is following along, which to me is a part of being part of these forums.

I can't tell if the pics I posted helped you, but they are helping me understand what's going on.
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