New FCC rules "Allow WMAS Technology That Enables More Wireless Microphones to Operate with Greater Efficiency"

[Jim Feeley]

I saw the Sennheiser marketing on WMAS last year. Are other companies adopting WMAS, or something like it? 

 

 

Press Release from today, Feb 15, 2024

(Link to report & Order below):

 

FCC EXPANDS OPPORTUNITIES FOR WIRELESS MICROPHONE USERS

New Rules Allow WMAS Technology That Enables More Wireless Microphones to Operate with Greater Efficiency

--

WASHINGTON, February 15, 2024—The Federal Communications Commission today adopted new rules to allow a new, more spectrally efficient wireless microphone technology to operate. Wireless Multi-Channel Audio Systems (WMAS) use spectrum more efficiently than currently available narrowband microphones, meaning more microphones can be used without allocating more airwaves. The rules will permit WMAS to operate on a licensed or unlicensed basis, while preserving the existing spectrum rights of others that share those frequencies.

 

Wireless microphones, which operate under the FCC’s technical rules for Part 74 low-power auxiliary station devices and Part 15 unlicensed devices, can be found in a variety of settings, including theaters and music venues, TV and film studios, educational institutions, conventions, corporate events, houses of worship, and internet webcasts. The new rules will allow WMAS to operate in the broadcast TV bands and 600 MHz duplex gap on both a licensed and unlicensed basis, and in other Part 74 LPAS frequency bands on a licensed basis.

 

WMAS will enable more wireless microphones to operate in the spectrum available (i.e., more microphones per megahertz of spectrum), which provides additional options when more microphones are needed. The rules do not alter the existing spectrum rights or expectations regarding spectrum access and availability as it relates to other authorized users that share the frequency bands with wireless microphone operations (including, for example, broadcast licensees, Wi-Fi, and white space device users).

Action by the Commission February 15, 2024 by Report and Order (FCC 24-22). Chairwoman Rosenworcel, Commissioners Carr, Starks, Simington, and Gomez approving. Chairwoman Rosenworcel issuing a separate statement.

 

###

 

Full Report & Order, and a couple other links on the FCC website here:

https://www.fcc.gov/document/fcc-expands-opportunities-wireless-microphone-users-0

 

 

[The Documentary Sound Guy]

That press release contains very little useful information.  The actual report is here:  https://docs.fcc.gov/public/attachments/FCC-24-22A1.pdf

The only manufacturers to comment on the report were Sennheiser, Shure, and Lectrosonics.  I would assume that means these companies are at least considering building something.  The rest of the commenters are mostly tech companies and industry groups.  Full list:
 

List of Parties Filing Comments
Comments
1. Aerospace and Flight Test Radio Coordinating Council, Inc. (AFTRCC)
2. Cisco Systems, Inc. and Facebook, Inc. (Joint Filers)
3. Microsoft Corporation (Microsoft)
4. National Association of Broadcasters (NAB)
5. National Telecommunications and Information Administration (NTIA)
6. Sennheiser Electronic Corporation (Sennheiser)
7. Shure Incorporated (Shure)
8. Society of Broadcast Engineers, Incorporated (SBE)
9. Waves Audio Ltd. (Waves)
10. Wi-Fi Alliance
Reply comments (due August 30, 2021)
1. Cisco Systems, Inc., Facebook, Inc., Qualcomm, Inc. and Intel Corporation (Joint Filers)
2. Lectrosonics, Inc.
3. Microsoft Corporation (Microsoft)
4. National Association of Broadcasters (NAB)
5. NCTA – The Internet & Television Association (NCTA)
6. Sennheiser Electronic Corporation (Sennheiser)
7. Shure Incorporated (Shure)
8. ViacomCBS Inc. (ViacomCBS)
9. Waves Audio Ltd. (Waves)

Here's what I was able to glean:  WMAS is about allowing wider channel bands for audio transmission as a way to allow more tightly packed channels.  This seems to approve channel sizes up to 6MHz in our usual UHF bands, with the expectation that that would include 18-24 channels of audio in those 6MHz.  Other frequencies allow up to 20MHz, but those probably don't affect us as much.

I'm confused by why the term "wireless microphone" is thrown around so much in the report, since there's little use for an 18 channel microphone.  This is about wireless transmission of many channels from the same source, so more like a standard for audio via a wireless "snake".  Call it wireless dante.  WMAS stands for "Wireless Multichannel Audio System" ... so it's many audio tracks bundled in a single wireless channel.  To me, that implies that there's a single transmitter for the whole channel, meaning single lav microphones are not the application here.  I don't think that allows for packing multiple transmitters more tightly (but it's possible I'm not thinking creatively enough).

So ... I think this is probably bad news for the way we currently operate.  How much intermodulation or noise floor does a 6MHz channel create?  How much wasted bandwidth will there be in the 600MHz UHF spectrum if people start using 6MHz channels to transmit three or four active tracks using technology capable of transmitting 18?  Will the companies designing WMAS devices shrink the size of the channel to suit what is actively in use?  I hope so, but I have my doubts.  Granted, these systems are designed for large venues, and hopefully we won't see too many in one place at the same time.  But I have to think that this is just adding more traffic and new applications to the UHF band.  Will a studio lot with 8 or 10 different mixers on site all want their own 6MHz chunk?  Given how Dante is currently being used, I can see that happening.  I think it's going to get even tougher to find pockets for single mic channels, and I think analogue modulations that are susceptible to intermodulation issues are going to get even more challenging to use.
 

[borjam]

8 minutes ago, The Documentary Sound Guy said:

So ... I think this is probably bad news for the way we currently operate.  How much intermodulation or noise floor does a 6MHz channel create?  How much wasted bandwidth will there be in the 600MHz UHF spectrum if people start using 6MHz channels to transmit three or four active tracks using technology capable of transmitting 18?

 

 

Actually, maybe it's not so bad, quite the contrary. Advanced modulation techniques can be more "gentle" as far as I know. Intermodulation is especially nasty with analog transmission that relies on continuous carriers.

 

That said, my brother tried transmitting Dante over a 60 GHz wireless link (full duplex  1 Gbps, 0.5 ms delay, or course perfect line of sight) and it worked like a charm.

 

[Johnny Karlsson]

Some interesting insights on WMAS here:

 

https://fohonline.com/articles/on-the-digital-edge/wmas-wireless-multi-channel-audio-systems/

[Matthew Steel]

At first it didn't make sense that multiple transmitters could share a large channel.  But having read a couple of articles and I think I understand better.  The individual transmitters would use spread spectrum and time division multiplexing.  Communication is bidirectional, and the base station can tell all the transmitters when and where they can transmit to avoid conflicts.

 

All the articles talk about using an entire TV channel, but conceptually, I don't see why a system could not be designed so that it could use less spectrum for fewer channels.  Also, it appears that the system is not an advantage until there are large channel counts.

[Michael Wynne]

WMAS approval allowing high bandwidth bi directional communication is the future for all remote control protocols such as frequency, gain settings, sleep modes, remote recording, etc. No need to rely for unstable and overcrowded 2.4 ghz technology used in todays tech.  It’s great news for all.

[The Documentary Sound Guy]

What is stopping manufacturers from using bidirectional communication under current licensing?  I have to admit, I'm very confused about the distinction between the licensing process and the technology here.

[Michael Wynne]

I believe it has to do with the per channel bandwidth limit, but I don’t know from an engineering stand point.  I’ve only heard of what’s possible now that they can utilize it and it seems to open new possibilities that weren't possible before.  Here’s an excellent video from Gotham Sound on the possibilities of WMAS with Shure.

 

 

[The Documentary Sound Guy]

50 minutes ago, Michael Wynne said:

I believe it has to do with the per channel bandwidth limit, but I don’t know from an engineering stand point.

 

I think the engineering standpoint is what's important though.  Control signalling requires a tiny fraction of full-bandwidth audio; I don't buy that it's a bandwidth limitation.  Zaxcom manages to transmit timecode embedded in their UHF signal under the existing license conditions, so it's not like it's unheard of to transmit metadata along with the main signal.  But nobody has done a two-way system that I'm aware of.

I didn't find the Gotham video very enlightening ... yes, you can do all kinds of things with 6MHz channels, but that's all this is really.  Everything else is unimplemented at this point, so it's all very speculative.  I don't see why it magically makes a control scheme possible that couldn't be implemented in a 200kHz channel.  Maybe this is what's necessary to allow devices to transmit on different channels but share a single "control" channel?  (though, that's effectively what is already happening, with the audio in UHF, and the control in 2.4GHz).

Don't get me wrong, I'll be pleased if WMAS allows control protocols to operate in UHF ... I just don't see how a change in channel allocation facilitates that.

[Dejan Ceko]