With #1 Charlie is quite right with the difference between filters & gel, which is a good idea in it's self to make the designation, of gel being for colour & filters for diffusion. As in days of yore they used red wine in a glass container to add colour to the light beam of candles & oil lamps. Where by they used silk to diffuse the light.
'Cinemiod' & 'Rosco' orginaly used dye doped Geletin as colour medium sheets. This was changed by adding Acetate to give it long life & reduce melting, called Geletan, which were available untill about the 80's. Then with the advent of higher temperature lights, they changed to the polycarbonate & the polyester sheets of today.
I cut my teeth on Cinemiodoriginally, which I believe was an offshoot company of Strand electrics. I knew by heart all the 100 or so colour number code & the coresponding colours, which ( have lost now & it is a useless bit of info these days?}
So the name Gel stuck for the sheets of colour medium used.
As an aside the normal sheet size gel also remains the same, as it was with Gelatin orignaly. Supposedly it was based on the size of Bakers trays used to produce the gel sheets & has not changed since.
Another bit of useless trivia is that Lee adopted the orginal Cinemiod colour code numbering & just added 100 to them to number thier product.
You will still come across the old Cinemiod & Roscolene Gels every now & then, that have survived. It is easy to pick them about by thier thickness & not being as mailable or as thin as the newer polyester gels.
Not being a 'Noisy' I couldn't advise on the radio Mic's, only to me it is Dependant on the receiver to pick up the transmission, so if the audio is transmitted in analogue, so long as you have a suitable receiver & audio system, it would work. Much the same as using a crystal radio, the fact that they have all changed to digital signals, the wavelength of the crystal radio can still be received & the wavelength is still there.
Well that's my zaks worth! [ AZak! - it's not even a Tra piece?] 
I hope it helps?
------------- Joe
Western Gondawandaland
turn right @ Perth.
Hear the light & see the sound.
Toi Toi Toi Chookas {{"chook [chicken] it is"}
May you always play
to a full house}
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