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2.4GHz general questions

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Andrew Taylor
2.4GHz general questions
on Sep 29, 2015 at 7:51:25 am

About 10 years ago I moved from digital video production to eLearning design (no hands-on audio or video development, just high level design and conceptualization).

I've moved back to more of a production role now, and as I'm updating my knowledge of tools and hardware, I discover there is a new player (new for me, at least) on the wireless mic arena with 2.4GHz systems like the ones below, listed from lesser known (at least, to me) brands to classic brands:

Neewer Dual Channel Camera Mount
http://www.amazon.com/Wireless-Lavalier-Microphone-Transmitters-Receiver/dp...

Audio-Technica System 10 Camera-Mount
http://www.audio-technica.com/cms/wls_systems/64268b9dcbed6cfd/index.html

Azden PRO-XD
http://www.azden.com/products/wireless-systems/pro-xd/

RodeLink Filmmaker Kit
http://www.rode.com/wireless/filmmaker

Shure GLX-D
http://www.shure.com/americas/products/wireless-systems/glxd-digital-wirele...

So, I'm trying to get a feel for these systems. When I left the field about a decade ago, UHF was basically the norm for higher end hardware. When I look at these systems, I see a mixture of features:
- some of them seem to have movable antennae (which was typical of VHF systems, improved with UHF)
- they seem to use a pairing routine like Bluetooth
- true diversity does not seem to be a selling point anymore
- automatic selection of channels/frequencies (less control, more automatization) seems to be the norm
- the fact that they work in the 2.4GHz spectrum (although the exact range is sometimes not clearly stated) seems to be advertise as a plus.

If you've read this far, I apologize for the length of the introduction, but these are some of the questions I have for anyone who has used/looked at these (or similar) systems:

- Is 2.4GHz really an improvement? Given the number of devices (WiFi, Bluetooth, etc.) that are already on this frequency, all around the world, is this really a cleaner spectrum?

- Is UHF (at 500MHz or 600MHz) still a good (or maybe better) option? I even saw some systems advertised at 900MHZ...is that common standard too? (I recently learned about the 700MHz spectrum changes thanks to another post on the forum)

- What do you call 2.4GHz anyways? Extra Ultra High Frequency (EUHF)?

Feel free to correct any of my misconceptions above as necessary :-)


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Ty Ford
Re: 2.4GHz general questions
on Sep 29, 2015 at 4:34:01 pm

Hello Andrew and welcome to the Cow Audio Forum.

Short answer:

http://tyfordaudiovideo.blogspot.com/2015/01/audio-technica-system-10-updat...

Wireless audio @ 2.4GHz is still in its infancy. Systems are less expensive. My own experience is that I've gotten about 150 foot range. Sound is good quality even though it's usually data compressed 2:1.

The Audio technica System uses multiple antennae, it offers audio bit redundancy and channel swapping if or when a particular frequency becomes a problem. Once it has changed operating frequency (noiselessly) it will again seek another standby frequency in case another problem occurs.

To my knowledge, no UHF wireless offers this type of redundancy (except for dual antennae)

Yes 700Mhz is gone in the US

There are a few holes left in 600MHz per an August 2015 change by the FCC.

500MHz seems safest for UHF.

Regards,

Ty Ford
Cow Audio Forum Leader

Want better production audio?: Ty Ford's Audio Bootcamp Field Guide
Ty Ford Blog: Ty Ford's Blog


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Andrew Taylor
Re: 2.4GHz general questions
on Sep 29, 2015 at 5:17:30 pm

If 500MHz is safest, then the Sennheiser ew 112-p G3 band A (516 MHz-558 MHz) or band G (566 MHz-608 MHz) would be a good option (band B is 626 MHz-668 MHz, not sure if interference may be an issue there).

Now, as you mention, some of these systems are less expensive (than an equivalent UHF system, for instance). Is that because of inherent weaknesses in the 2.4MHz technology, so manufactures are trying to gain product acceptance by offering lower prices, or is it just that this technology (2.4MHz-based hardware) is cheaper to produce?

Nice AT blog entry, by the way.


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Ty Ford
Re: 2.4GHz general questions
on Sep 29, 2015 at 6:44:27 pm

Andrew,

If you're going G3, I would stick with A and G. The ME2 lav that comes with the G3 can easily be bettered by choosing the MKE-2 or other lavs. Sanken and Countryman lavs will normally result in better sound as well.

Again, I'm not sure that all 2.4 GHz systems are equal. The AT one sounds VERY good to me. I have one now as a fall back and test model and, so far, it's doing very well.

There is one problem I have found with 2.4GHz wireless systems and that the shielding on the mic itself. If you hold one of the really small AT lavs near the transmitter, you can hear a HF whine. Normal (visible) lavs, no problem. The Rode has the same problem with the lav that comes with the Rode Link 2.4GHz system.

You don't normally hold the lav next to the transmitter, so unless you try to use the system with the mic wrapped around the transmitter, like a plant mic, you should be OK.

Regards and thanks for the mention of the blog,

Ty Ford
Cow Audio Forum Leader

Want better production audio?: Ty Ford's Audio Bootcamp Field Guide
Ty Ford Blog: Ty Ford's Blog


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Andrew Taylor
Re: 2.4GHz general questions
on Sep 29, 2015 at 7:02:33 pm

Thank you for the extra info. Interesting that I never thought of using a lav as a plant mic. I always assumed a lav would not have the reach, so for anything that was not on the body I would automatically go to a shotgun (hiding it within the frame whenever possible, on a pole otherwise).

In retrospect, maybe it was the cheap lavs I used that did not have the reach :-)


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Richard Crowley
Re: 2.4GHz general questions
on Sep 29, 2015 at 10:54:05 pm
Last Edited By Richard Crowley on Sep 29, 2015 at 11:01:57 pm

Antennas at 2.4GHz are only around 2 inches long, so you are more likely to find the antenna(s) completely enclosed within the transmitter housing (and often that goes for the receivers, also).

All digital systems require some kind of "pairing". Whether this is visible to the user or not is a decision the designers made for you.

Actually many (most?) of the 2.4 GHz products have significantly MORE DIVERSITY than older generations of VHF and UHF systems. For example, most of the 2.4GHz systems that I have seen have TRIPLE DIVERSITY:

1) They have SPATIAL diversity with two separate antennas, much as what we thought of as "diversity" back in the old VHF/UHF era. For example the Audio Technica System-10 has TWO separate antennas inside the transmitter plastic shell.

2) They have TEMPORAL diversity. The same block of audio data is sent at least twice at different times so that if the first is lost or garbled, the second can be substituted.

3) They have FREQUENCY diversity. When powered-on they automatically scan all 12-13 channels to pick the optimal channel for primary operation, as well as a secondary channel as an immediate back-up. When when forced to switch to the back-up channel, they then search and select a NEW back-up channel. All of this happens very fast and completely hidden to the end-user.

The main advantages of 2.4GHz include:

1) 2.4GHz is one of the "ISM Bands". https://en.wikipedia.org/wiki/ISM_band

These bands are reserved IN ALL COUNTRIES and protected against future encroachment by greedy government authorities (like the FCC in the US) who make billions of dollars by selling off RF bandwidth to the highest bidder.

That means that they can be expected to be more "stable" for a few years with some assurance that you investment in gear won't be wiped out next month by a mendacious but clueless bureaucrat.

It also means that your gear will work in ANY COUNTRY. You don't have to look up obscure (and changing) rules and laws if you work in multiple jurisdictions.

2) The technology (integrated circuit "chipsets", antennas, even software.) are ubiquituous with the flood of consumer gear that uses 2.4GHz. Most notably including WiFi and Bluetooth (as well as cordless phones and other wireless gear.) That makes it MUCH MUCH less expensive both to develop and manufacture 2.4GHz digital gear. And we see the direct result of this with all these new 2.4GHz digital audio kits.

3) Automatic channel selection. Because they must "play nice with others", these systems automatically scan all the 12-13 available WiFi channels for the best and "next best" channels for primary and back-up operation. Furthermore, because the transmitter also receives, and the receiver automatically transmits, they can communicate interactively with each other to coordinate "pairing" automatically.

4) Because of the "2-way" communication between the transmitter and receiver, and the extra bandwidth available, extra nifty features can be easily added, typically simply with "firmware". For example: remote reporting of transmitter battery charge/life. And most brilliant: remote cancelling the transmitter MUTE mode!

Of course, nothing that good is without the disadvantages which include:

1) The 2.4GHz band is overloaded with very many devices, users, and applications. Most notably, these include WiFi and BlueTooth. But note that most microwave ovens also operate on 2.4GHz. You may have noticed that your Bluetooth gadgets are intermittent or even completely fail when with 1-2m of an operating microwave oven. And, of course, the more WiFi and Bluetooth traffic there is, the more a 2.4GHz wireless mic will have to compete for channel availability.

https://en.wikipedia.org/wiki/List_of_2.4_GHz_radio_use

So, operation in a modern office building would be more likely to be problematic than out in a rural area, for example. IMHO, this is the biggest unknown for these 2.4GHz products. How effective they will be in the presence of lots of 2.4GHz competition. However, so far I have not seen any widespread (or any at all for that matter) reports of operational problems from RF congestion.

2) Limited channels. There are only 12 (or 13 in some territories) WiFi channels available. A full-speed computer WiFi connection gobbles up 5 adjacent channels, but the 2.4GHz wireless mics use only a single channel (plus another standby, backup channel). Because the systems use microcontrollers at each end, they are designed to automatically scan the immediate landscape to identify usable channels, so they attempt to make the most of this competitive situation.

Note that there are WiFi band analyzer apps for IOS and Android which will show you signal strength on all 13 WiFi channels in graphic form on your device screen. You can install one of these (free) apps to help evaluate the local 2.4GHz landscape in your favorite venues.


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Andrew Taylor
Re: 2.4GHz general questions
on Sep 29, 2015 at 11:18:32 pm

Thank you for a very thorough write up on 2.4 GHz systems :-)


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Ty Ford
Re: 2.4GHz general questions
on Sep 30, 2015 at 1:05:19 am

Excellent response Richard!

Want better production audio?: Ty Ford's Audio Bootcamp Field Guide
Ty Ford Blog: Ty Ford's Blog


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