Why digital

Home > Learning Center > Why digital

Why digital

Copsey believes regulators are pressing for digital because "it's a buzzword."
"The regulatory bodies are pushing for digital because they think if mobile phones can do it, radio microphones should be able to too," agrees Patel.

TG 17 generated the digital standard "because we were asked to by the manufacturers, but I'm not convinced that radio microphones need to go digital. At least, not yet," says Copsey.

"Analogue radio microphones can work in 50 channel slots without problems in a spectrum efficient manner," says Copsey. Most non-technical people thought digital would be more efficient and more cost effective, because that is how it performed with CDs and DTV, but he says the reality is different.
Because radio microphones need real time transmission, you can't use the most efficient compression as compressing the signal causes delay. "This problem is most noticeable with lip synchronisation in live performances," he says. "The delay is inherent in any form of compression system, but native rate [uncompressed] systems need greater bandwidth." Of course, analogue radio microphones do use a form of compression (companding), but that is effectively lossless.
At present, a radio microphone channel uses 200kHz, but digital would need more bandwidth to deliver the same quality, even using compression, says Patel. "Digital can't be more efficient because radio microphones need more than 100 dB dynamic range compared to 40 dB signal-to-noise ratio for vision. It is also easier to compress video than audio, especially when trying to synchronise audio to video, the delay is quite crucial on a live set," he says. The delay means it will also be difficult to mix standard wired microphones with digital. Given that most applications for radio microphones are live, this leaves digital dead for now. "We have two conflicting requirements of: no lip synch delay; and compressed audio. You can't do both with the technology we have now," says Patel. He believes the technology will arrive eventually, possibly in about five years.

Gill believes it will be a couple of years before digital kits are in use, but users won't want to buy equipment that can't be used live, so "manufacturers have to crack that problem. If we used more spectrum, you wouldn't need to reduce the bit rate so far, but the target bandwidth is the same as analogue, so it needs considerable reduction [compression]," says Gill.

The US allows 800kHz bandwidth for digital radio microphones at lower power (half a milliwatt), but this would limit users to only about five radio microphones working together in a multi-channel situation.

Within the 1785 - 1800 MHz band, Patel believes that the current specification (with about 400kHz bandwidth per digital channel), would give eight to ten channels in Europe's 15MHz, depending on the technology people employ. "If you allow greater compression, with greater delay, you would get more in. It is probably better to stick to analogue until the technology is worked out," he says.
There are only a few digital radio microphones available yet, such as one Sennheiser sells in the US, although that is believed not to be a big seller.

Copsey sees spectrum efficiency becoming increasingly important as users are charged for bandwidth, but digital technology can't give that efficiency in real time - yet. Besides, digital costs more and can't compare with the multichannel abilities of analogue. While an analogue system can easily cope with 32 channels at a single event, he doubts whether digital will be able to deliver the same ability cost effectively, or in a spectrum efficient manner. "I'm not convinced that digital technology has much to offer the high-end user with multi-channel systems," he says.

"Power consumption is also quite a challenge," adds Gill.

Digital is currently confined to the 1785 - 1800 MHz band, "until we have more experience and can look at the compatibility of digital radio microphones with both analogue and digital TV and more importantly other radio microphone systems," says Copsey. Work on this is starting in the next six months.

The CEPT (Conference of [46] European Post & Telecommunications administrations responsible for radio spectrum) FM (Frequency Management) 41 Project is looking at not only radio microphones, but also ENG/OB frequencies generally, including microwave links, talkback, and wireless cameras. It is endeavouring to make sure there are frequencies for all these things after the switch from analogue to digital and is aiming for a common solution throughout Europe, says Gill.

In Germany, which has 7MHz channels for TV (within 8MHz bands where the remaining 1MHz is used for radio microphones), there will be a problem switching to digital, as the new DTV standard is 8MHz for TV, so there will be no more gaps for radio microphones. The UK has always shared on a complicated basis as it already has 8MHz TV channels, but the broadcasting of DTV alongside analogue has reduced the spectrum for radio microphones.

Gill says FM 41 is arguing the case for specific allocation of the UHF spectrum for radio microphones. He is reasonably optimistic that a European-wide solution will be achieved, otherwise national systems will have to be devised yet again.

Digital

Primer

Wireless lapel

Reality show

Where to buy

Contact Us

Links & Resources

Site Map

Wireless microphones | Digital microphones | Learning Center | Site Map | Links | Contact | Home

Copyright © 2010

Copsey believes regulators are pressing for digital because "it's a buzzword."
"The regulatory bodies are pushing for digital because they think if mobile phones can do it, radio microphones should be able to too," agrees Patel.

TG 17 generated the digital standard "because we were asked to by the manufacturers, but I'm not convinced that radio microphones need to go digital. At least, not yet," says Copsey.

"Analogue radio microphones can work in 50 channel slots without problems in a spectrum efficient manner," says Copsey. Most non-technical people thought digital would be more efficient and more cost effective, because that is how it performed with CDs and DTV, but he says the reality is different.
Because radio microphones need real time transmission, you can't use the most efficient compression as compressing the signal causes delay. "This problem is most noticeable with lip synchronisation in live performances," he says. "The delay is inherent in any form of compression system, but native rate [uncompressed] systems need greater bandwidth." Of course, analogue radio microphones do use a form of compression (companding), but that is effectively lossless.
At present, a radio microphone channel uses 200kHz, but digital would need more bandwidth to deliver the same quality, even using compression, says Patel. "Digital can't be more efficient because radio microphones need more than 100 dB dynamic range compared to 40 dB signal-to-noise ratio for vision. It is also easier to compress video than audio, especially when trying to synchronise audio to video, the delay is quite crucial on a live set," he says. The delay means it will also be difficult to mix standard wired microphones with digital. Given that most applications for radio microphones are live, this leaves digital dead for now. "We have two conflicting requirements of: no lip synch delay; and compressed audio. You can't do both with the technology we have now," says Patel. He believes the technology will arrive eventually, possibly in about five years.

Gill believes it will be a couple of years before digital kits are in use, but users won't want to buy equipment that can't be used live, so "manufacturers have to crack that problem. If we used more spectrum, you wouldn't need to reduce the bit rate so far, but the target bandwidth is the same as analogue, so it needs considerable reduction [compression]," says Gill.

The US allows 800kHz bandwidth for digital radio microphones at lower power (half a milliwatt), but this would limit users to only about five radio microphones working together in a multi-channel situation.

Within the 1785 - 1800 MHz band, Patel believes that the current specification (with about 400kHz bandwidth per digital channel), would give eight to ten channels in Europe's 15MHz, depending on the technology people employ. "If you allow greater compression, with greater delay, you would get more in. It is probably better to stick to analogue until the technology is worked out," he says.
There are only a few digital radio microphones available yet, such as one Sennheiser sells in the US, although that is believed not to be a big seller.

Copsey sees spectrum efficiency becoming increasingly important as users are charged for bandwidth, but digital technology can't give that efficiency in real time - yet. Besides, digital costs more and can't compare with the multichannel abilities of analogue. While an analogue system can easily cope with 32 channels at a single event, he doubts whether digital will be able to deliver the same ability cost effectively, or in a spectrum efficient manner. "I'm not convinced that digital technology has much to offer the high-end user with multi-channel systems," he says.

"Power consumption is also quite a challenge," adds Gill.

Digital is currently confined to the 1785 - 1800 MHz band, "until we have more experience and can look at the compatibility of digital radio microphones with both analogue and digital TV and more importantly other radio microphone systems," says Copsey. Work on this is starting in the next six months.

The CEPT (Conference of [46] European Post & Telecommunications administrations responsible for radio spectrum) FM (Frequency Management) 41 Project is looking at not only radio microphones, but also ENG/OB frequencies generally, including microwave links, talkback, and wireless cameras. It is endeavouring to make sure there are frequencies for all these things after the switch from analogue to digital and is aiming for a common solution throughout Europe, says Gill.

In Germany, which has 7MHz channels for TV (within 8MHz bands where the remaining 1MHz is used for radio microphones), there will be a problem switching to digital, as the new DTV standard is 8MHz for TV, so there will be no more gaps for radio microphones. The UK has always shared on a complicated basis as it already has 8MHz TV channels, but the broadcasting of DTV alongside analogue has reduced the spectrum for radio microphones.

Gill says FM 41 is arguing the case for specific allocation of the UHF spectrum for radio microphones. He is reasonably optimistic that a European-wide solution will be achieved, otherwise national systems will have to be devised yet again.

Links & Resources

Site Map