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Old May 5th, 2008, 10:43 PM   #1
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UHF vs. VHF

What are the differences between wireless UHF and VHF lav mics?

I went to a store today, and said a used an azden which was a vhf, i got pretty good sounds, or so i thought since i'm new to audio, but he just mentioned things about the signals.

Is there a difference in sound quality?
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Old May 6th, 2008, 07:05 AM   #2
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Quote:
Originally Posted by Kevin Ta View Post
What are the differences between wireless UHF and VHF lav mics?

I went to a store today, and said a used an azden which was a vhf, i got pretty good sounds, or so i thought since i'm new to audio, but he just mentioned things about the signals.

Is there a difference in sound quality?
There is and there isn't. There's nothing inherent about the transmission frequency itself that would make a UHF unit sound better than a VHF unit. However the other drawbacks of VHF have sent the pros almost exclusively to UHF and the manufacurers of the top quality gear aimed at that market have followed suit. As a result, the VHF offerings on the market today are almost exclusively budget and consumer level gear with limited features and overall lower quality. UHF is less prone to interference, dropouts, and noise and can be packaged as smaller devices - shorter antennas and that sort of thing.

FYI, the general consensus is that the least expensive wireless for serious work currently on the market is the Sennheiser G2. The Azden might be okay for some purposes but personally I wouldn't risk it for any serious project.
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Old May 6th, 2008, 11:21 AM   #3
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I'd second what Steve has said, but might also add that Audio Technica has recently come out with their AT1800 series, and the early reports on them are very favorable. While not a ton cheaper than G2's they are slightly so.

Incidentally - My experience with the AT88W vhf series has been pretty good - provided the talent is not more than 30 or so feet away from the receiver. That said, if there are no "second take" possibilities, you might want to consider the G2 or similar.
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Old May 6th, 2008, 11:59 AM   #4
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Agreed RE: the 88w--it may or may not be quite usable for your particular application. As Chris sort of starts to say, though, it's probably not the best option if you need a significant amount of range or if your subject matter is critical and cannot be captured in more than one take. The 88w--because it's VHF and only has two selectable transmission frequencies--is much more prone to drop-outs and interference than a pricier UHF multi-frequency system. On the plus side, it doesn't have a compander and so the audio it produces can sound quite good if you use a decent lav with it.
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Old May 6th, 2008, 12:47 PM   #5
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Here is a good overview of the differences between VHF and UHF in wireless systems:
http://www.sweetwater.com/expert-cen.../d--06/14/2001
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Old May 8th, 2008, 01:41 AM   #6
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Thank You all for your insight! I'm learning something new everyday from this forum.
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Old May 8th, 2008, 08:12 AM   #7
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I suppose it's worth mentioning that UHF systems are inherently shorter range because "free space path loss" is greater at higher frequencies. In fixed systems this is compensated for by a higher gain antenna which can be smaller at UHF but with a these mics the antennas are all (VHF or UHF) basically 0 dbi (or less) and so path loss is a factor. FSPL can be overcome with more transmitter power but the FCC limits that and higher transmitter power means shorter battery life. It can also be overcome by improved noise performance (noise figure) in the receiver and that used to be a problem as low noise figure transistors were harder to produce at higher frequencies. These days 3 dB noise figure is nothing at VHF or UHF though the UHF transistor will cost a couple of bucks more. As significant today as noise figure is interference immunity. Here we don't mean co-channel interference but adjacent channel interference. The popular Sensheiser 100 series generally span 2 UHF TV channels and it is unlikely that both will be assigned in a particular area so we use the other. But the channel we are not using can very well have a transmitter in it with hundreds of killowatts of peak power and we are trying to work with a transmitter that runs 10's of milliwatts. FSPL is the savior here (the TV transmitter is much farther away and, as we are at UHF it is greater than it would be at VHF) but darn good out of band rejection and wide dynamic range (high IIP3 if there are any other engineers out there) are required. The need to build receivers that work in this kind of environment has driven lots of development (thanks to the cell phone industry) and so the necessary components are available to the manufacturers. But at a price.

Another consideration may be that as the UHF wavelength is shorter it propagates somewhat better through buildings but, on the other hand, is more attenuated by things like tree leaves (especially if they are wet).

Greater congestion at VHF is probably the main factor that has driven the manunfacturers to UHF as better UHF components have become available to them. Shortly the new digital TV sytems will make much of the UHF spectrum available to other services and the manufacturers are not happy with this. A little review of their websites will give you more insight into this situation (they'd like you to write your congressman). Given that this is such a small industry I'd expect it to lose against the wireless carriers (huge industry) with the result that I expect the mic makers to move up into the GHz range where there are other advantages like the ability to use all digital spread spectrum techniques (everyone is on the same frequency but each user has a unique code).
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