How to Record Live Audio Like a Pro
The purpose of this blog is to give the amateur-to-novice user a list of tips when recording live audio. These tips may come in handy when recording things like presentations, seminars, sermons, and other events. With a little extra legwork, you will achieve above average sound quality results by following some of simple steps outlined in the blog. Below are seven areas to address to achieve higher quality live audio recordings.
Most don’t get a choice of the room they are recording in, but if you do, make sure you choose something based on sonic value, not on aesthetics. A few things to listen for in the room are the room noise itself, reverberation, and diffused areas. First, walk into the room and close your eyes, simply listen to the room. Do you hear fluorescent lights humming extremely loud, an electrical room buzzing next door in the background, an industrial sized air conditioner that turns on and turns off, or possibly even street traffic? If this is the case, it might be something you deal with in the recording. Microphones are sensitive, and in basic terms what you hear is what you get. Locate the problems, and then position your setup around these unwanted sounds.
Second, walk around the room and talk out loud in it, maybe even clap your hands a few times. Does it sound like a cave, or even worse, does it echo like a tile bathroom? If it’s a large room such as a church, you might even incur a slight echo. Most rooms won’t be a nuisance to record a business seminar or conference in, but if you’re dealing with reverberation or echo, keep in mind this could make working with a wireless microphone a major problem. Rooms that reverberate or echo can provide a healthy dosage of feedback when microphones are moving throughout.
Thirdly, walk the room and listen for diffused areas. A diffused area would be a section of a room that sounds dead, or has no reverberation. A great exercise would be to clap your hands and listen for reverberation. The less reverberation you hear, the more diffused the area. This could be because of a large rug or possibly asymmetric walls. The point being is that the more diffused a room is, the more conducive it will be to recording live audio. Also, keep in mind that the human body will act as a diffuser in the room.
Once you find the most diffused area, you can begin to set up your equipment. A mixing board, interface, and live CD recorder will make a good basic setup, while a more advanced setup may include receivers, effects processors, and more. Read more about this below in the Signal-to-Noise ratio section.
This has to be one of the easiest things you can do to instantly improve the quality of your recording. There are literally hundreds of microphones out there, so which should you choose? The quick answer is that the most cost effective choice would be the Shure brand dynamic microphone, preferably the SM-58 or SM-57. You have probably seen these used at major events like Comic Con, SXSW, and on the lectern of the President of the United States. These are microphones that shouldn’t cost more than $20 a day to rent.
If your audio engineer or the company you’re renting from doesn’t have either of these microphones or something better, I recommend searching for new help. Looking to splurge a little, Shure makes a Beta series of live condensers (87A, 87C) and dynamic microphones (58A). Remember that if you go with a condenser, it will require phantom power. Please keep in mind there are many other choices out there, so do your research.
When choosing a wireless microphone and/or lavalier, you need to consider several different factors. First, take your budget into account. Wireless microphones will at least double your rental or purchase rate per microphone, if not more. Secondly, how mobile will your speaker actually be? Many speakers love the luxury or “cool factor” of a wireless microphone, but will remain in the same sitting or standing position the entire time. Why add chaos to your recording when you don’t need a wireless. Point being is that a wired SM-58 is much more effective than using a lower quality wireless, or using a wireless in a room that’s not sonically friendly (see Room Sonics above).
Third, is dealing with the headache factor. Wireless microphones are wonderful devices, but they can add a lot to the grief factor to your recording. For example, they can add unwanted signals, hum, room noise, and even cut out in areas of the room. A wireless lavalier can incur the same problems, but since they are clipped to a person’s shirt, it can add additional unwanted elements. Nothing is worse than playing a cat and mouse game with a public speaker who is moving or bumping their lavalier microphone. It adds unwanted noise and could possibly destroy your signal to noise ratio.
If a wireless mic is required, Shure or Sennheiser brand microphones are great choices. With a little prepping, these two brands should alleviate some of the headaches. But always thoroughly test your wireless or lavalier microphone throughout the room when prepping. Personally walk the microphone and speak in every area of the room. Find out where feedback and noise might be lurking, so you can coach your public speakers. Also, always have new batteries (usually 9v or AA) on hand in case disaster strikes.
Signal to Noise Ratio (SNR)
In very basic terms, Signal to Noise Ratio or (SNR) is the range between the reference signal (signal you want, like your voice) and self-noise (unwanted signal, like room noise). For example, if you listened to a recording that you made, and heard your voice being drown out in unwanted hiss or room noise, you would have a bad SNR. If your recording were clean with your voice and no room noise, you would have a good SNR. A detailed explanation of SNR can found through a simple search on the web. Achieving a decent SNR can be done by managing two things, signal flow and gain structure.
The signal flow, or how your equipment hooks up, should use the path of least resistance. Keep the setup minimal, and let your equipment do what it does best. In other words, don’t hook up a bunch of extra equipment or run microphones though multiple gain structures (i.e. mixing boards or FX). The most simplistic example would be Diagram 1A, located below, which uses no processing. This is the safest way to ensure clean signal flow to your recording.
However, with a somewhat experienced engineer, Diagram 1B might allow for better SNR. The difference between 1A and 1B is compression and limiting, which can also be referred to as dynamics. What they potentially add is more control over the volume of your speaker’s voice. However, if you don’t know how to use these, it’s highly recommended that you do your research before trying. They can easily destroy a recording when used improperly.
Gain structure is a pretty complicated topic, but for recording a business seminar or a panel, we will simplify it by using an example. In this example we are recording three individuals speaking on a discussion panel. Start by hooking the three microphones to your mixer, dedicated microphone preamp, or Tascam digital audio workstation using XLR cabling. First, make sure you have a microphone signal. Then hit the Solo or PFL button for each microphone on the mixing board, and have the first individual on the panel solely give a microphone check.
At this point, use the microphone gain or trim on the incoming channel to lock in a level on your meter that peaks around -5db on the meter. Meters can vary in sensitivity, so make sure you don’t break 0 db. Do not use the master volume as your level reference, use the incoming channel meter (i.e. channel 1). Then after all three individuals, give a Solo or PFL microphone check that peaks around -5db, try to get the panel of 3 speakers to simulate a real discussion.
It is at this point you will monitor your total master level on the mixing board or I/O. With normal conversation going on from your panel, the master level meter shouldn’t peak higher than 0db. If it does, you will need to go back a step and dial back the microphone gain or trim on the louder individuals until you can achieve the highest individual microphone trim levels without the collective group of 3 panel speakers level peaking over 0db.
If the master level meter barely passes over 0db a few times, it’s okay, due to a feature called headroom. Headroom is the space between the preferred operating level (in this case 0db) and failure (better known as distortion or clipping). Manufactures leave different amounts of headroom on different equipment. So how much headroom do you have? That is like asking how many miles do you have left once your gas light comes on in your car. Trial and error is the best way to find that answer, but always err on the side of caution. A common technique that can curb levels near 0 db with little fear of it going over, is done by using compression and limiting as shown in diagram 1B above.
When recording a live event, it is a great idea to have a secondary device. A handheld linear PCM recorder or even an iPhone can be your best friend in the event things go wrong. Most phones have the ability to record hours of uninterrupted audio at a high frequency rate. For example putting an iPhone in the middle of those who are speaking is not a bad idea. This ensures you have back up audio that you can replace the original with, if your main device crashes. Usually the best placement of the secondary device is nearest the person who will be speaking the most. Please remember to turn off everything on your phone, or put it in flight mode.
One of the biggest keys to recording a public speaker or lecturer is to remember that you only get one crack at it. There isn’t any going back, hanging on, or redoing. Once the audio has been recorded, it’s nearly set in stone. For lack of a better phrase, once the audio has been spoken, “it is what it is,” at that point. I realize this seems quite obvious, but the reason I write this blog is because I have encountered one too many projects where the person recording was flat out lazy, or uneducated about the process. This resulted in recordings with qualities such as distortion, feedback/hum during speech, and a terrible SNR. These are not qualities that can be edited out at a later date.
A great way to get ideas for setting up a room, or positioning of microphones for your recording, would be to do a internet search of pictures of some of the bigger seminars or panels. A few Google image searches are “Comic Con Panel,” or “panel of speakers.” These will give you a visual representation of what your seminar might look like. Again, all of this might seem obvious, but a reference point or visualization might have you rethinking how to setup your presentation.