#2 Prepping multiple wireless mics for a television shoot.

Hi Friends,

This is my second blog! Got a few comments for my first one! Many thanks to all those who commented.

Before I continue, I just thought I should clarify that in my blog, I am posting my personal views and comments. I could be completely wrong about some technical aspect I may write about... please do correct me if you think so. My blog is aimed more towards students who have just passed out from an Institute and are trying to make a career in the Film or Television Industry in the field of Sound Recording and Sound Engineering. I just want to share my experiences of the past 33 years with my readers.

Based on the feedback that I received for my first blog, I have decided to write a little bit more about wireless lapel mics.

It is not uncommon to have 10 to 15 Sennheiser G3 wireless lapel mics on a television multicam show. So how do I go about setting them up for the actual shoot?

No two television shows are the same. Each show is different, but whether it a television show or a feature film shoot, my method of CHECKING my wireless lapel mics remains almost the same.

I will first, briefly outline the steps I follow to do this.

• Connect all the gear up.
• Check all mics individually on PFL.
• Check all mics for PHASE. 
• Check all receivers to see if they are receiving RF signal on both antennas.

Now every step a bit in detail.

I am starting off at the stage where my console is powered up, the appropriate scene recalled, and my receivers are connected. My assistant makes sure that all settings on the receiver are identical (output gain, no eq, etc…) and frequencies are setup on the Tx and Rx according to the Intermodulation free frequency chart that is provided by Sennheiser. With all Tx off, no RF signal should be showing up on the receivers, which means we have a clean RF spectrum to work in.

I start off by getting all the wireless microphones next to me in my control room, near my console and from where I can see the receivers of all the mikes too. I bring out my headphones and start testing and checking my wireless mics, one at a time. I power up the first wireless transmitter and hold the microphone capsule close to me, and monitor the channel on PFL. First off, I listen for any hum or buzzing noise. If OK, then I proceed further by speaking into the mic. As I monitor my voice in the headphone, I gently move the cable just below the microphone head to make sure that the cable has no breaks. If the microphones are old and much abused, then you may hear a crackling noise every time, the cable just below the microphone head is moved. If the cable below the mic head is OK, I then slowly move downwards, gently letting the cable pass through my fingers, sort of as if straightening the mic cable. All along, I am listening for any crackle on my headphones. When I reach the connector that connects the mic to the transmitter, I gently shake the connector, to check for any cable breaks or bad soldering in the connector. If there is a problem in the connector, there could be a nasty crackle. Then I press the buttons on the G3 transmitter. Some Tx give off a thud when the buttons are pressed. If that is OK, I then gently move the antenna wire a bit at the base. I also cover the antenna wire completely in my hand (by cupping the wire) and observe the RF signal on the receiver. The RF may drop marginally, but it should not drop off completely. Now I know that the microphone top, cable and Tx, all together are working fine. I now bring the mic top a bit close to my mouth and speak a bit loudly into it and monitor the input level on the meter on the Tx. The meters on the Rx also show the same level. I adjust the gain according to the output the capsule is giving, leaving sufficient headroom for talent to scream or shout.

This is my procedure for the first mic. I follow the same procedure for as many lapel mics as I have. Once I have gone through all the mics and adjusted their input gain according to my voice, I hold all the microphones in my hand...that is I keep all the lapel tops about 4 inches away from my mouth and speak loudly into all of them, simultaneously. If the mics are all fine, you will find that the gain settings on the transmitter are more or less the same, that the output coming from the receivers is also more or less the same and the input gain settings on the console are also more or less the same. This is usually the case when you have all brand new mics and brand new Tx and Rx. But in real life, you seldom get all mics in good condition. So when you notice that one channel is showing a setting that is far too different from the settings of the other mics, you can suspect something is not quite right.

So my advice to all, is to always have extra Tx and Rx in your setup. And use only those which are good and working well.

Now I critically listen to each mic on PFL by rapidly changing from lapel 1 to lapel 2 to lapel 3. All mics are still being held about 4 inches away from my mouth as I speak into all of them simultaneously. This gives me an idea of the tonal quality of each mic. (I keep EQ off and HPF off on all channels when I do this). Once the tonal quality of all mics is acceptable, I move over to PHASE checking.

I assume that the ch 1 mic phase is correct and proceed to check all other lapel mics against it.

To do that, I monitor on my headphones, a mono mix of Ch 1 with the other lapels, one by one. I bring up the fader of ch 1, and as I speak into the microphones, I bring up the fader of ch 2. In effect, I am now listening to a mono mix of my voice from ch 1 and ch 2. If the phase of the two mics is correct, my voice will sound the same, just a bit louder since two mics are sending the same signal and adding up. But if the phase (or polarity of some cable, somewhere in the chain) is reversed, the quality of my voice will change when the two mics are mixed together. The voice will become tinny and the bass will disappear. If you are not sure as to what I mean by tinny and no LF, I suggest you deliberately change the phase on ch1 and then listen to the resultant mix with the mic on ch2. Once you have heard and learnt what happens, when two mics out of phase are picking up the same signal, you will realise why it is important to have all mics in phase.

If ch 2 is fine with ch 1, I then move on to the other mics, one by one….that is ch 3 against ch 1, ch 4 against ch 1 etc. I check all mikes one at a time with my ch 1 mic. (If I find that all the other mics are showing an out of phase signal when mixed with ch 1, then my assumption that ch 1 was OK was incorrect).

So, if all Tx are in good working condition, the tonal quality of all mics is acceptable, and the phase of all mics is correct, then we only have the final step left, which is to ensure that our receivers are set up properly in terms of RF reception.

Now, I send all mics to the studio floor where they will actually be used and watch the receivers carefully. All receivers should show good RF reception on both antenna channels, A and B. If an antenna wire running from the antenna on the studio floor, to the splitter in the control room is faulty, you may end up running your system on only one antenna. It is very easy to overlook such a fault in the system. Sometimes it is better to disconnect both antenna cables and then attach only one antenna at a time. Observe that the correct RF channel (A or B) is showing good RF while the other should show poor RF. Then disconnect this antenna wire and connect only the second antenna to the second input connector and observe the RF from this second antenna coming into your system. This way, you can ensure both antenna wires are sending you a proper RF signal. Once I am certain that my antenna wires are all correctly connected and RF signals coming in properly, I am almost ready to go.

One last check. I switch off all Tx one by one, and now observe the receivers. The RF should drop off completely on all receivers. If some stray RF is being picked up by some receiver, then I change the frequency on the Tx and Rx of the offending channel, but by picking a compatible frequency from the Sennheiser frequency chart.

This is how I check my wireless system.

Some pointers to keep in mind:

• Always use fresh batteries in the Tx at the start of the day. When changing batteries, change both batteries, that is don’t mix old and new batteries in a transmitter. 
• Always ask for more mics that required. You never know when one of them will fail or malfunction, so it is always better to keep extra mics, checked and ready for use. 
• Make sure frequencies on Tx and Rx are set according to the freq chart provided by Sennheiser (or Lectrosonics, in case of feature film work and you are using Lectros). 
• Check each Tx and its microphone, slowly and thoroughly. You don’t want to change a mic in the middle of a shoot because you were careless and did not spot a bad Tx or bad cable. 
• Check phase of all mics when using more than one lapel mic.
• WHEN CHECKING PHASE, JUST MAKE SURE THERE IS NO EQ IN THE CHANNELS AND NO HPF. WE WANT FULL LF FROM THE MICS, TO IDENTIFY PHASE ISSUES. ALSO IF YOU HAVE SWITCHED ON DAN DUGAN AUTO-MIXER IN THE SIGNAL PATH, MAKE SURE THAT IT TOO IS BYPASSED. AND USE GOOD QUALITY HEADPHONES, WHICH HAVE A GOOD LOW FREQ RESPONSE.
• On Lectrosonic receivers, there is a phase invert option in the menu. There is also a phase invert option on the channel input on Sound Devices 788 / 688 type of recorders. So first check that all settings are normal before you start phase checking of mics in this kind of a setup. 
• On Lectrosonic Tx and Rx where the antennas can be detached, it is important to have the correct length of antenna on both Tx and Rx to get the best possible range. There is a chart available on the Lectro website listing the length (depending on the block). Lectro Tx and Rx have many other settings that one has to be aware of, so it is best to read up about Lectro from their website. 
• Remember, the microphone is the first place where sound is converted from acoustical energy to electrical energy. It is most important to get things right at that very stage. 
• Also understand that once a wireless mic is put on talent, it is going to be out of your control. You cannot always easily access the Tx and its buttons to make changes in the settings. The wear and tear on microphone cables and the Tx is dependent on how that actors are behaving. They could be running, jumping, dancing, rolling on the floor etc...and that makes the Tx vulnerable to failure. Always keep extra mics!
• Remember, it is your responsibility as a recordist to check your equipment thoroughly and not simply blame an attendant or the vendor, if a fault arises in the middle of a shoot. Check your equipment thoroughly, anticipate problems and have backups and extra gear whenever possible. 

There are still some problematic issues that might get overlooked. Sometimes, the antenna on the Tx looks good on physical examination, but may be faulty and not be performing as per specifications, resulting in poor RF range. Wireless lapel mics can work fine for an hour and then suddenly fail to work. Sweat from artists can result in RF dropping or mics failing. I am not even discussing RF issues you may run into when you have another shoot nearby. You also need to check the frequency of PA / FM mikes (floor manager mics) and the frequency of any IFB units that you may be running simultaneously on your shooting floor. Use the chart provided by the manufacturer to set your frequencies. Write down all frequencies being used on a sheet of paper and keep it handy. You never know when you may need to refer to this information. Intermodulation distortion is another subject, but I am not writing about it here now. Check and double check your mic before it goes up on talent, and you will minimise the risk of failure.

SOUND FOR FILM AND TELEVISION by TOMLINSON HOLMAN is an excellent book, where all these fundamentals are very beautifully explained. I highly recommend this book to all students and to all those who are just starting out in the field of sound recording for film or television.

Hope this information has been of some use. Until next time.

CC

E-mail: cheerag.cama@gmail.com
Twitter: @cheragc
Website: www.cheeragcama.com