Save Our Spectrum - Possible Solutions
Digital wireless microphones – do not compress!
Wireless microphones can of course also be digitalised! But to broadcast the same kind of quality provided today by analogue microphones would take roughly the bandwidth of a TV channel (8 MHz)! An 8 MHz wide TV channel can easily take 10 analogue microphones. Digitalisation here would therefore be very uneconomical at the moment and a waste of valuable spectrum. Work is currently underway on processes that enable digital microphones to operate in the bandwidth occupied by analogue microphones. This would allow an increase in quality, though not a gain in spectrum!
Wireless microphones are at the start of the production chain, and compression processes cannot be used here. Transmissions have to be of the highest quality to retain all the freedom available in terms of editing and managing contributions.
If transmissions are compressed, as is the case when programmes are transmitted via digital TV stations, and then edited and compressed again for broadcasting via the transmitter, it is impossible to control the digital image and sound. The viewer is aware of this which devalues the product and makes it unusable.
Today, old mono recordings can be converted into acceptable stereo recordings because the old mono material exists in an uncompressed form, allowing complete freedom in processing and therefore conversion into other formats with minimal losses.
Digital microphones – delayed
The analogue signal of a microphone capsule comes first. This is digitalised in the microphone and then transmitted, received and processed further. This digitalisation process takes a few milliseconds. A speaker or artist’s digital monitor signal also takes milliseconds to process. If you add all these computing times together, a speaker would hear his words with a light echo which would be irritating and his words would lose their power.
This is also completely unthinkable and unacceptable for a music act because a few milliseconds’ time lag would make the performers go out of time! A process therefore has to be developed where processing times are inaudible – for uncompressed data. Digital mixing desks also have processing times, slowing down the signals being processed: the whole chain has to be observed continually here and brought in line.
Requirements of digital microphones and monitor systems
Digital microphones and monitor systems are not allowed to take up more spectrum than the familiar analogue systems! An analogue wireless microphone takes up around 200 kHz; a digital system currently two to three times as much: 400 – 800 kHz. With high accumulating data flow, high-quality modulation processes also have to be used. These are very complex and have to offer the same reliability as the current analogue systems.
A digital system also has to open up opportunities for improving quality: today sound is broadcast in SD (Standard Definition) in CD quality with 16 bit resolution. In future it will be HD: High Definition. Studios are already working now with 24 bit, some with 32 bit. Digital wireless systems are expected to provide this quality in future – in turn this increases the data flow rate and requires more bandwidth for transmission or even more complex modulation processes.
This just leaves the unavoidable time lag. It clearly has to be reduced to below a threshold noticeable by those involved. Fast computers and intelligent signal processing open up prospects for solutions. The fact that transmitters and monitor receivers have to remain small and battery-operated also needs to be taken into account! All wireless microphone and in-ear monitor system manufacturers are furiously working on meeting these requirements.
What is certain however is that while the digitalisation of wireless microphone technology does not need fewer frequencies than it has at the moment, it clearly presents more opportunities for quality improv
ement.
Alternative production frequency ranges for wireless microphones?
The UHF range is currently almost exclusively conducive to the operation of microphones – a few of them are still operated in the VHF range. The UHF range has the advantage of good signal propagation and low levels of interference.
Radio and TV broadcasters have the right to use mainly the UHF range which means secondary users like reporting teams find it very easy to obtain frequencies. It is in the interest of TV broadcasters to have their content produced for subsequent distribution via their transmitters around the country. Broadcasting programmes around the country alone brings in revenue for TV stations.
Avoiding frequency ranges means finding suitable ones first - everything has been given out - and obtaining authorisation to operate there as a secondary user. Radio has very few additional frequencies that would be possible and these could not carry the entire production load.
As wireless microphones are used more or less exclusively inside buildings, it is possible to imagine using the frequencies primarily available outdoors for radio relay links as secondary users: in the L-Band (with 1.5 GHz). Compatibility studies by the European Union have been initiated but the results have not yet been published.
What could these frequencies be used for? Mainly for in-ear monitor systems, consequently “freeing up” the UHF band from these applications.
Systems worn on the body (bodypacks) are not suitable as absorption by the body and scenery means there is insufficient range in this frequency band. Hand-held microphones however would be conceivable.
The 1.785 – 1.800 GHz frequencies used for reporting are also available and can be used across Europe (except for the UK and Ireland 1.79 – 1.80 GHz). Field tests will be carried out on this in the near future in practical trials to optimise appliances.
Wireless microphones also need the UHF range because of propagation conditions and the ranges required for their practical use.
2.4 GHz microphones
Is this frequency range an alternative? Not for professional users who require high quality signals without interruptions, which is not a given in this frequency range as anyone is allowed to transmit there, such as Bluetooth, WLAN etc. This means there is a very high risk of uncontrollable interference.
With WLAN data transfer, this interference does not apply because if a data packet is erroneously picked up by the receiver, it continues to be requested by the transmitter until it is available error-free. This process ensures data security but also causes delays in transmission, which may not be permitted in the audio sector as it results in an unfeasible increase in latency.
Frequency coordinators
That wireless microphones are crucial in productions is increasingly evident as event organisers use frequency coordinators to ensure that their event runs smoothly and without interference.
Unlike many digital services, wireless microphones have 100% power-on time for the event’s duration and no impairment of any kind is allowed during operation. The short-term loss of a link during an important statement by someone in a position of responsibility would be embarrassing, while it could lead to a cultural event being stopped and a production becoming unusable.
Frequency coordinators identify interference and intermodulation-free frequencies for their planned event and these are allocated to the appliances of the people involved. Attention is paid to local availability to avoid any conflict with transmitters that are already in operation. People wanting to report on the event register themselves in advance and are also allocated frequencies. If they turn up at short notice, security usually informs the frequency coordinator as they enter an event venue for a frequency to be allocated.
What resources do wireless microphones need?
These are specific examples of just a few major events. Take a look round however and it is clear that a great many events of this kind are taking place in politics, culture and sport which are currently coordinated and operated through frequencies that are still available in the UHF band, maintaining the variety of opinions and colour of our cultural landscape.
The cultural sector is also an essential factor in the economy and should not be overlooked. According to Bernd Neumann, Minister of State for Culture (Focus Interview 01/2008), the proportion of the gross national product represented by the cultural and creative industries is around 125 billion euros: the same as the automotive sector!
Day-to-day business is less spectacular, but is going on practically everywhere in press conferences and events in conference centres and hotels, in parliaments and companies during discussions and presentations, in theatres, concerts, studios and location shoots, all the way to fitness studios.
Around 40 links have become the standard in theatres and concerts. On top of this there are monitor links for the protagonists, which are often used at press events and for interpreting purposes too.
Three blocks are needed...
for every three TV channels, a total of 72 MHz covering day-to-day business. 20 links can reliably be used in each of these blocks, meaning for example that 40 wireless microphones and 20 in-ear monitors can be operated in parallel. Three blocks are to be distributed across the UHF spectrum, similar to that in Directive 91/2005, thereby minimising mutual interference and making optimal use of the available spectrum.
Channel gaps are currently available for these applications: 47x 1 MHz = 47 MHz. In addition to this, there are six channels from Directive 91/2005, i.e. another 48 MHz. These six channels have no 1 MHz channel gap, so six need to be deducted from the 47 channels = 41. If you add all these together, this gives a spectrum of 89 MHz used by wireless microphones.
However there are plenty of applications in theatres, concerts, conference centres, universities and TV productions that do not manage on this spectrum and “buy in” additional unoccupied TV channels from the Bundesnetzagentur. This is still possible at the moment as gaps remain in the UHF spectrum, but it is expected that these gaps will be closed in future, mainly by DVB-T applications. How a major event like the ones mentioned above can be carried out in Germany is questionable.
The trend towards more wireless technology remains undiminished. In recent years the sector has recorded double-digit growth. The assumption is that more than 700,000 such installations are being used in Germany, with more than 6 million across Europe.
As they have become easier to operate, are very reliable and mean economies can be achieved at events, this trend will continue. An event’s organisation and development can only adapt to changed circumstances at short notice if it has wireless technology!
A spectrum for wireless microphones is needed because they play a crucial role in communications and mean that many venues are actually useable.
It is worth everyone affected by this campaigning to keep the UHF spectrum.
Users of wireless microphone technology:
Broadcast - TV applications
Professional Applications
Communications
Public facilities
Private facilities
Military
Trade Unions
Banks
Insurance Companies
Health Services
Is your application included in this list? If not, then please write and let us know!
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