New Radio Mic Section for Rough Guide to Location Audio - comments please

[Ben Edwards]

Hi, this is a follow on from http://www.dvinfo.net/forum/all-thin...guide to audio. It looks like a section on radio mics is needed. They seem to be a minefields and should only be used if absolutely necessary. Here is the first stab I have made at it with the help of a sound recordist I know, comments welcome but please be genital;). The guide (Rough Guide to Location Sound Recording) has also been changed to incorporate comments from this forum and that work will continue.

RADIO MICS

Using Radios

Radio mics transmit the audio signal from a mic worn by the contributor as radio waves over a short distance to the receiver, which is connected to a mixer or plugged directly into the camera. They are often used for interviews as they allow the contributor to move around freely. They are particularly useful for presenters (especially if they are ‘out and about’). They should only be used if absolutely necessary, if it is possible a wired lavalier is always preferable.

The average working range for a radio mic varies between around 60 and 150 feet, depending on make and model. The cheaper ones have one antenna and a shorter range. The more expensive ‘diversity’ mics have two so are less susceptible to interference and can be used over a greater distances. The batteries may last several hours but the range can start diminishing after only an house or so. This is generally not an issue as they are usually used at very close range, but this needs considering.

However, their use can also be fraught with problems, not least the issues of crackling/signal drop out and interference from other kit on the same frequency. The radio mic frequency band is shared by various different users, TV and video radio equipment being only some. You may be in range of someone else using the same frequencies as you, so continual monitoring is necessary as this may happen at any time. If it does you can change the frequency (the system will have several).

As well as setting levels on the camera/mixer in the normal way, radio mics have their own levels to set, making setting them up even more complex. The Transmitter/mic pack often has a input/mic trim level. The Receiver pack can also have an output level control. The radio mic has its own noise floor so the level of the transmitter/mic must be strong enough to get well above this but must never peek.

Tip: When setting the radio mic levels, remember that the sum of these levels add some noise to the channel and it is important to set your levels correctly and evenly before starting the job. Try to make sure the transmitter audio input level is not too high, leaving a bit of headroom is preferable and the receiver output level should be adjusted if possible to ensure it is not too quiet.

You are effectively setting up to 2 extra levels (depending on which system you use) so the potential for getting it wrong is increased. This is the reason that they should only be used if you need the mobility or cable free operation. With sit down interviews a wired solution is preferable. Reading the instructions for the microphone is essential. Do some web research for the make model you have. A beginner can get good results but it is risky. A good sound recordist a massive benefit and will minimize the risk.

Makes of Radio Mic

There are many good makes of radio mic available (i.e. through Ebay). Manufacturers include Sennheiser, Micron, Zaxcom, Audio Technica and Audio Limited. Best of the budget range has to be the Sennheiser EW112-p G3 (around £500). Next up is the Micron Explorer 100 Series 16CH - SDR116 which is a true diversity system, on sale at some places for under £1000. Second hand ones can be considered but read the next section and make sure you are not getting one which will be/was obsolete in 2012.

Licences and Changes in the Air

Using radio mics in the UK requires the user to hold a License. By the end of 2012, there are changes taking place in the frequency allocations for personal radio equipment. The frequency band changing from Channel 69 to Channel 38. This means that new equipment is now replacing old. You may be excited by the low prices of radio mics that are on sale for on Ebay but buyer beware - as of the end of next year, the old frequencies will begin to get filled up by telecoms digital transmissions and Channel 69 is expected to become literally unusable (and in any case, illegal to use

Regards,
Ben

[John Willett]

Originally Posted by Ben Edwards

Hi, this is a follow on from http://www.dvinfo.net/forum/all-thin...guide to audio. It looks like a section on radio mics is needed. They seem to be a minefields and should only be used if absolutely necessary. Here is the first stab I have made at it with the help of a sound recordist I know, comments welcome but please be genital;). The guide (Rough Guide to Location Sound Recording) has also been changed to incorporate comments from this forum and that work will continue.

Hi Ben,

A good idea; but, unfortunately, quite a bit needs changing. You do seem too negative about radio and some comments are based on very old designs - for example, the range of a good radio does not diminish as the battery goes down - a good modern radio (eg: G3 series) used a DC/DC converter that always supplies the correct voltage to the equipment. As the battery goes down, the DC/DC converter draws more and more current until the battery is extinguished and the transmitter will then die very quickly. Which is why you should always use new / freshly-charged batteries for each event.

So ............

Originally Posted by Ben Edwards

RADIO MICS

Using Radios

Radio mics transmit the audio signal from a mic worn by the contributor as radio waves over a short distance to the receiver, which is connected to a mixer or plugged directly into the camera. They are often used for interviews as they allow the contributor to move around freely. They are particularly useful for presenters (especially if they are ‘out and about’). They should only be used if absolutely necessary, if it is possible a wired lavalier is always preferable.

This needs changing:

Radio mics transmit the audio signal from a transmitter to a receiver, which is connected to a mixer or plugged directly into the camera. There are three types of transmitter: A pocket transmitter with a small tie microphone (often called a lavelier mic. in the USA), a hand-held transmitter (like a normal microphone with a bult-in transmitter), or a plug-on transmitter (this converts a normal microphone into a radiomic. and are mostly used for converting a long-handled reporter mic. into a radiomic., or for making a wireless fish-pole). They allow the user to move around freely, un-tethered by a cable. They are particularly useful for presenters (especially if they are ‘out and about’).

Originally Posted by Ben Edwards

The average working range for a radio mic varies between around 60 and 150 feet, depending on make and model. The cheaper ones have one antenna and a shorter range. The more expensive ‘diversity’ mics have two so are less susceptible to interference and can be used over a greater distances. The batteries may last several hours but the range can start diminishing after only an house or so. This is generally not an issue as they are usually used at very close range, but this needs considering.

The working range for a radio mic. can be up to one or two hundred metres in line-of-sight, though it is best to keep to 50 metres or less for reliability. Receivers can be "diversity" or "non-diversity", a diversity receiver uses two antennas and the antenna with the strongest signal is the one used and the receiver switches antennas silently to the strongest signal (nb: the G3 pocket receiver uses the output cable as the second antenna). Cheaper systems tend to have less selectivity on the receiver, and fewer can be used in the same location. Modern radio systems use DC/DC converters which give full power to the transmitter until the battery dies; this can happen very quickly, so do not try and use batteries from the previous day. Older or cheaper systems do not use a DC/DC converter and the transmission power will drop quite quickly, it will then level off for a while before slowly dying. Again, a good reason not to use batteries too long.

Originally Posted by Ben Edwards

However, their use can also be fraught with problems, not least the issues of crackling/signal drop out and interference from other kit on the same frequency. The radio mic frequency band is shared by various different users, TV and video radio equipment being only some. You may be in range of someone else using the same frequencies as you, so continual monitoring is necessary as this may happen at any time. If it does you can change the frequency (the system will have several).

The transmission frequency must be carefully chosen as interference with another transmitter could occur. Each manufacturer will have a recommended frequency plan of frequencies that will work together and this should be adhered to. Always switch on the receiver first at a new location or scan to find out if anyone else is transmitting. Do not switch on a transmitter before checking as you could cause interference to others. At large events pre-planning of frequencies is essential. The radio mic frequency band is shared by various different users, TV and video radio equipment being only some. You may be in range of someone else using the same frequencies as you, so continual monitoring is necessary as this may happen at any time. If it does you can change the frequency (most systems will be switchable). Be aware that the human body absorbs - if the antenna of a pocket transmitter touches the body you can attenuate the signal by as much as 70dB, vastly reducing the range. Keeping the antenna off the body by as little as 1cm will get most of this back. Consider mounting the transmitter with the antenna pointing down as this can often help.

Originally Posted by Ben Edwards

As well as setting levels on the camera/mixer in the normal way, radio mics have their own levels to set, making setting them up even more complex. The Transmitter/mic pack often has a input/mic trim level. The Receiver pack can also have an output level control. The radio mic has its own noise floor so the level of the transmitter/mic must be strong enough to get well above this but must never peek.

As well as setting levels on the camera/mixer in the normal way, radio mics have their own levels to set. The Transmitter will have a sensitivity control to maximise transmission level without distortion. The microphone has its own noise floor so the sensitivity of the transmitter must be set to give a good output but must never peak. The Receiver pack will normally have an output level control, many can output either microphone level or line level; wherever possible it is always best to output line level and go into a line input.

Originally Posted by Ben Edwards

Tip: When setting the radio mic levels, remember that the sum of these levels add some noise to the channel and it is important to set your levels correctly and evenly before starting the job. Try to make sure the transmitter audio input level is not too high, leaving a bit of headroom is preferable and the receiver output level should be adjusted if possible to ensure it is not too quiet.

Tip: When setting the radio mic levels, remember that the sum of these levels add some noise to the channel and it is important to set your levels correctly and evenly before starting the job. Try to make sure the transmitter audio input level is high, but not too high, leaving a bit of headroom is preferable to clipping and distortion and the receiver output level should be adjusted to as high as possible without distorting the input of the receiving equipment. Line level is better than mic. level - if you do have to use a microphone input make sure that no phantom or plug-in power is being sent into the receiver, or you have a receiver with blocking capacitors that will prevent this power doing any damage.

Originally Posted by Ben Edwards

You are effectively setting up to 2 extra levels (depending on which system you use) so the potential for getting it wrong is increased. This is the reason that they should only be used if you need the mobility or cable free operation. With sit down interviews a wired solution is preferable. Reading the instructions for the microphone is essential. Do some web research for the make model you have. A beginner can get good results but it is risky. A good sound recordist a massive benefit and will minimize the risk.

You are effectively setting up to 2 extra levels (depending on which system you use) so the potential for getting it wrong is increased. This is the reason that they should really only be used if you need the mobility or cable-free operation. With sit down interviews a wired solution is preferable. Reading the instruction manual is essential. Do some web research for the make model you have. A beginner can get good results but it is risky. A good sound recordist is a massive benefit and will minimise the risk.

Originally Posted by Ben Edwards

Makes of Radio Mic

There are many good makes of radio mic available (i.e. through Ebay). Manufacturers include Sennheiser, Micron, Zaxcom, Audio Technica and Audio Limited. Best of the budget range has to be the Sennheiser EW112-p G3 (around £500). Next up is the Micron Explorer 100 Series 16CH - SDR116 which is a true diversity system, on sale at some places for under £1000. Second hand ones can be considered but read the next section and make sure you are not getting one which will be/was obsolete in 2012.

Makes of Radio Mic

There are many good makes of radio mic available. Manufacturers include: Sennheiser, Audio Limited, Micron, Lectrosonics, Zaxcom and Audio Technica. Best of the budget range has to be the Sennheiser evolution G3 series (ew112-p G3 - around £500 - or the ew 100 ENG G3 which is the same kit but with an added plug-on transmitter). Next up is the Micron Explorer 100 Series 16CH - SDR116 which is a true diversity system, on sale at some places for under £1000. Second hand ones can be considered but read the next section and make sure you are not getting one which will not be usable for you after 2012.

Originally Posted by Ben Edwards

Licences and Changes in the Air

Using radio mics in the UK requires the user to hold a License. By the end of 2012, there are changes taking place in the frequency allocations for personal radio equipment. The frequency band changing from Channel 69 to Channel 38. This means that new equipment is now replacing old. You may be excited by the low prices of radio mics that are on sale for on Ebay but buyer beware - as of the end of next year, the old frequencies will begin to get filled up by telecoms digital transmissions and Channel 69 is expected to become literally unusable (and in any case, illegal to use

Licences and Changes in the Air

You MUST make sure you are aware what frequencies are available in your country and find out if they require a licence. It is very dangerous to take radio microphones across borders without first checking the legality as you could find them impounded by Customs - in the same way, it can be dangerous to purchase radio systems from another country as you could easily end up with something that is illegal in your own country.

In Europe there is a small frequency band - 863MHz to 865MHz (in Ch.70) that is available for use licence-free in every ETSI signatory country. This frequency band will not change and will continue into the future. In practice up to about four frequencies can be used intermodulation-free. Cheap systems only two or three, though Sennheiser can get six frequencies in G3 systems.

All other frequencies require a licence in the UK. There are two types of licence available: "co-odinated" (fixed site) or "shared" (mobile). In the past the shared frequencies were 14 fixed frequencies in TV channel 69, though in practice only four to six were usable in cheap systems, though better systems could get eight or twelve working together. This frequency band will become illegal during 2012, but is guaranteed up until the end of the London Olympics. The replacement frequency band is channel 38 which is currently used by radio astronomy and some radar stations. These will cease at the end of 2011 and the full Ch.38 will be available for radio microphones. Up until the end of 2011, channel 38 can be used, but with exclusion zones (the largest is centred on Jodrell Bank radio telescope). A licensed user must first look up the availability at his location and if it is within an exclusion zone, then frequencies in Ch.39 or Ch.40 will be allowed (the look-up table will advise). From January 2012 onwards, Ch.38 will be fully available for shared frequency use and Ch.39 and 40 for licensed co-ordinated (fixed site) use only.

After the shut-down in 2012 Ch.69 will be licensed for a Europe-wide wireless broadband system (including many other TV channels) and will be totally unusable and illegal for radio microphones.

You may find many second-hand systems for sale cheaply - be aware that if these are old Ch.69 systems they will only be of use if they are under 10mW and can be switched to the de-regulated 863MHz band.

Full details on UK licenses are on the JFMG website.

Their is also lost of information on the change-over on the BEIRG website.

The website of the Institute of Broadcast Sound is also useful.

________________________________________________________________

OK - that's my take on the guide.

It is meant to be constructive and does correct some mis-information in the original.

I hope it helps.

[Karl Winkler]

John,

Kudos on the great edit. And with your experience in the UK with the changing regulations, your advice in that area is particularly helpful to this UK-based primer. I didn't see anything to add to your changes.

[Ben Edwards]

John,

Wow - thank a lot for taking the time to help, will include your edits. . I guess it seems negative because it is beginners guide and people often seem to head straight to using radios when wired is safer. I do however think that they probably should only be used where wired are not practacle, rather than as a first choise for all interviews.

Ben

[John Willett]

Originally Posted by Ben Edwards

John,

Wow - thank a lot for taking the time to help, will include your edits. . I guess it seems negative because it is beginners guide and people often seem to head straight to using radios when wired is safer. I do however think that they probably should only be used where wired are not practacle, rather than as a first choise for all interviews.

Ben

Wired is definitely safer - but a well planned radio link need not give any problems at all.

The biggest problem is people going to a radio tie mc. when booming a mic. would give far better and more natural sound.

[Alastair Traill]

Quote: -
"Here is the first stab I have made at it with the help of a sound recordist I know, comments welcome but please be genital;)."

It is a long time since anyone wanted me to be genital!

[Garrett Low]

Originally Posted by John Willett

The biggest problem is people going to a radio tie mc. when booming a mic. would give far better and more natural sound.

This is very quickly becoming a bigger and bigger issue especially with small independent productions which I do a lot of. IMO it is due largely to misinformation being spread by many online articles and websites that give out what appears to be "expert" advice. More and more I run into young and new producers and directors that just say "we'll use wireless lavs" to pick up 90% of their dialogue. When I try to explain to them that it would be worth the extra preproduction time to plan out how to capture audio correctly when blocking each scene they don't want to take the time. Then, when they get into post they can't understand why their production just doesn't sound that good.

Kudos to you Ben for taking the time to research the subject and solicit input to make sure you're article is as accurate as possible.

-Garrett

[Tony Davies-Patrick]

There was talk of Ofcom closing the 69 Channel to wireless/radio mic users by end of the Olympics, but at least that hasn't happened and all is still OK in UK.

OFCOM have announced that they are extending access by three months to the channel range 61 to 69 until the 31st of December 2012. JFMG will continue to co-ordinate the use of channels 61 to 68 during this period.

Here is a link to more details:

http://www.jfmg.co.uk/pages/equip/Radiomics/dtv.htm

Here is diagram showing the movement from Channel 69. This is a big headache, especially due to myself and thousands of others who have many sets of Chanel 69 wireless units. Hopefully I'm going to be able to still use them next year as well.

Click on the thumbnail to enlarge image.