Drive-In - recommended FM transmitter power?

[Marin Zorica]

I did some drive in shows in past few years and i hope there will be some more in next month....

Anyway, here i can get temporarly licence for drive-in transmitter at very cheap cost and is legal. You need to apply some three weeks in advance and check for clear frequency, than you pass location data, frequency etc data in request to regulatory angency and if everything is ok they send you licence with parametres and some fee to pay

From tech point of view, i always used L/C/R summed to either mono if transmitter is mono or stereo like L+C, R+C. In not rate ocasion i notticed that mono is best way to ho, because car systems (speakers placement, some audio processing etc inside of car) are "doing" something to audio you don't want to have while listening dialogue. Some classic compresson was added on main mix to keep max modulation of transmitter up to 75khz, because some radio hates to get clipped. And plus extra compresson on C channel before mixing so you can raise dialogue level, so in case some music etc on L/R, Center will not be masked by other.

As for other processing like optimod, omnia, bw etc i think is not needed at all, while i was working on radio station, it quite different story than to pass clear signal to listener cars, and most of todays fm broadcast processor will sound soooo boosted, which on other hand is go for fm radio.

Mainly i have used half lambda dipole and 50 or 100mW by licence which is enought to cover field like footbal field with good signal without interference. Tried also some cheap to $100 china ebay transmitters but they are no go, since most, like 90% are based upon small bh1441 ic intended for wireless headphones. So either i used professional fm tx, or my own tx i developed back in days with pll and 1w output.

BW is great unit or either some used pro rvr, elenos fm exciter you can find, it cost something like $300 but it will not give you any problems or interference during show.

[Marcel Birgelen]

Yes, that's the problem, L/R/Ls/Rs/LFE will smother Center in a summed mixdown compressing scheme. I think in the X-Air, one could setup a combination of compressors and limiters on a channel basis that would take care of that.
E.g. have a ducker/sidechained compressor on L/R/Ls/Rs/LFE fed by the center channel. That would always keep the center channel on top IF there is signal on it. Sounds like a lot of fun trying...

This is something I can't even do with the Optimod, as it's just a single program/2ch-stereo device.

I toyed around a bit more last night. I kept the surrounds at -3dB, put the LFE at +4dB and the center at +1.5dB... not based on any real science, just intuition. I ran the stuff through the Optimod and listened to the output on the analog port in monitor mode. Apparently, the monitor port has a delay of 5ms, while the signal to the transmitter has a delay of 15ms. The monitor port doesn't apply stuff like comb filtering and other "FM-processing", but should give a pretty adequate rendition of what you would hear on the radio.

After reading a bit through the manual, I wasn't as intrigued as I was before, the amount of settings are pretty comprehensible. The unit is more of a set-and-forget type of thing, doing a lot of stuff pretty decently right out of the box. It's obviously optimized for radio broadcast channels though. I wasn't displeased with the preliminary result after more or less randomly toying around with the settings. It's clear that the thing will put some emphasis on speech and essentially puts "the midnight mode" (you know, that evil compression setting found on your average home cinema thingy) on the entire mix, which is, what I guess, is what it's supposed to do.

I don't have the transmitter here yet, so, I'm still excited to hear how it will sound through an actual car stereo like a little kid... you know, first time ever we're (hopefully) doing an actual "Auto Kino" around here.

[Mark Gulbrandsen]

If it were me I would probably look to use a DSP so that I can create my own "air chain" of limiting, compression, and combining.

Sean, If you combine a USL JSD-60 and the TX30 that is essentially what you have, except in commercial products that directly interface.

[Sean McKinnon]

That would be great if the TX-30 was readily available and you had a license for a signal with that range.

The nice thing with Q-Sys is that for the price of a DCP-300 you get a fully configurable DSP (mix down, limiting, highpass, PEQ, whatever you want, Automation Controller, 16 Channels of AES in on 8P8C connectors, 8 Channel HDMI in and Decoding, 16 Channels of Analog in (phoenix, 8 configurable as outputs if needed), 1 "mic" in on XLR, 1 Stereo 3.5mm in, and 8 analog outputs plus monitor and HI/VI outputs on phoenix, Also a physical main fader knob and a mute button. 4 Relays and GPIO are also included. For a budget conscious customer I used some old SPDT and SPST toggle switches in an old rack plate for selecting Feature, Non-Sync, Bluray, and Mic On/Off. Throw in a $200 Part 15 certified FM transmitter and you have everything you need for a drive in and it is upgrade-able for the future. Hell, you can add a UCI license for less than $150 and give them the ability to operate the entire thing from their cell phone!