One important old adage about audio for video is ‘bad audio kills good video’. This is true: there’s nothing more irritating than lousy audio in a video one’s watching.
Droning brings additional issues for audio acquisition – propeller, motor and wind noise. Very little of whatever audio your drone’s recording system will produce will be usable, so, the use of external recording systems will be necessary. This article will deal with some audio basics and situational considerations.
Field audio system requirements are basic – a recorder, microphones and headphones. Most recorders are digital and can vary in recording capacity from stereo to multi-channel units. Honestly, a stereo recorder would work fine for most situations. While not absolutely necessary, external microphones are also more desirable since one can choose specific microphone types depending on the shoot requirement. Decent quality headphones are vital to monitor what is being recorded.
One of the most important reasons for recording audio separately are the options of how to use this audio during the post-production of the video. One of the best examples I can share why this is important we recently shot a construction video where there was a lot of heavy-equipment activity occurring, and it was essential to capture the sound of the equipment as ‘background’ audio to be used to fill in the blank spaces between dialog pauses, and then as a ‘fill’ or bed underneath the narration, albeit mixed in at a lower level as to not mask the narration.
To elaborate on this, note the next time when watching ‘Star Trek – The Next Generation’ (or any space show). There is continuous HVAC noise present when there are shipboard scenes (not to mention all the beeps and other simulated mechanical and electronic noises), giving the illusion of being aboard such a vessel. Another example is while watching nature videos: since the cameraman can’t be close to the lions while filming, the sound effects of the lion’s actions are added in post-production, but the ambient noise is captured by the audio recordist out in the field as an underlying audio layer. While it might seem to be ‘cheating’, audio background noise adds to the ‘audio cues’ we continuously hear and rely on to make the video sound more realistic.
There are several handheld recorders that come with built-in mics, usually stereo. These are nice because the need to select specific mics for recording is removed – ‘point and shoot’, as it were. Most of these have preset microphone configurations that will give a decent stereo ’field’, where when listening back to the recording (especially with headphones), one experiences a ‘you are there’ listening experience.
Most recorders also have auxiliary mic inputs which allow the user to select more specific microphones. Sometimes the onboard recorder mics will not be sufficient for the shoot requirements, and the recordist will need to use more appropriate mics. My personal recommendation is to use a recorder that has ‘XLR’ inputs. XLRs are a universal professional connector type and can accommodate a wide variety of mics. They’re mechanically stable, rugged, and robust.
We need to discuss microphones at this point. Microphones come in 2 basic types – dynamic or condenser. Dynamic mics are self-powering, whereas condenser mics require external power to function. Dynamic mics are good for higher sound-pressure environments but may not be as ‘nuanced’ or sensitive as condensers.
Condenser mics require ‘phantom power’ to energize the mic capsule and function. They can be more sensitive than a dynamic mic, and care has to be taken to not overload the signal when recording. The phantom power voltage, supplied by the recorder, varies from 3V to 48V. This voltage is also removed prior to being recorded so that only the sound source is passed.
Both types of microphones also come in several different pickup, or ‘polar’ patterns. There are several different polar pattern types, the basic ones used being omnidirectional, cardioid and hypercardioid. Omnidirectional mics record sound equally from all directions. Cardioid polar patterns are more directional (usually in a heart-shaped pattern, hence the name) and will not record sound from all directions equally. Hypercardioid (more commonly known as ‘shotgun’ mics) are highly directional and will reject most sound that is not the direction this mic is pointed at.
Microphone polar patterns are usually determined by the design of the mic, although some mics have switchable polar patterns. Polar patterns also ‘color’ the mic’s tonal characteristics: omnidirectional mics have no ‘sound coloring’ because they record equally from any angle. Cardioid mics will have noticeable changes in sound quality (characteristics) as the mic moves away from the desired sound generating source (most noticeable, bass response declines faster). Hypercardioid mics will have even more radical tonal response than a cardioid as the mic moves off-axis form the sound source – but also have an unusual polar pattern idyosyncracy of having some ‘rear’ polar pattern response developing not seen in cardioid mics.
Mic cable quality is also important because not just any cable will suffice. Use high-quality cables and keep the length as short as possible to prevent RF or other induced transient signals. This matters to dronists since many times, you’ll be flying in high-RF and electrically-noisy environments. Shorter, high-quality mic cables also help keep the noise level down (all audio electronic systems generate self-noise for a variety of reasons, eg: ‘tape hiss’).
Recorders are important for the obvious reasons. My recommendation is a recorder that is stereo, has internal mics but also XLR inputs, removeable recording media (SD style cards, etc but something that is easily available out in the field), level meters and easily-accessible recording and headphone level controls. Battery power is also necessary, and I also recommend something that uses easily-available AA or AAA batteries. Rechargeable power-packs (usually a Li-Ion battery) have inherent faults because one may NOT be able to find a replacement when a fresh battery is required.
Most recorders have some type of menu system to access various functions of recording parameters. For me, it’s important to have control of the recording sampling rate, baseline recording level, low-frequency cutoff (gets rid of low-frequency audio signals like ground-hum and windscreen noise), phantom power on-off, automatic level control (minimizes distortion from excessive audio peak signals), even storage card capacity. Sampling rate determines the absolute recording quality in terms of frequency response: users will want to choose a sampling rate that’s optimal for the post-production environment one’s working in. 44.1K or 48K are pretty standard for post-production environments. Any higher sampling rates are overkill for most of the situations we work in.
One odd thing about older digital recorders- they may not be able to use larger-capacity SD cards now available. I found this out the hard way on a shoot once. This is not a problem to worry overly about – low capacity cards (1 to 8 Gig) are a lot cheaper than what they were 5 years ago, and recording digital audio requires a LOT less storage capacity than digital video.
The last link are headphones. There are many choices here, so the best considerations are noise-rejection, comfort and durability. Noise-rejection here means blocking external noise as much as possible while recording to ensure accurate monitoring of what’s being recorded. Comfort is important since one might be wearing headphones for extended periods, so hearing fatigue can become an issue. Durability is self-evident: the dronist’s working environment can be challenging at times and our gear has to be durable and robust in additional to being high quality.
Make sure to have headphone adaptors to match the recorder’s headphone output. There are two headphone connector sizes – 3.5mm (1/8”) mini and ¼ “ ‘guitar’ plug. Most portable recorders I’ve encountered use the mini headphone connector. If you prefer using a headphone set that has ¼” jack (traditionally found on home stereo systems), I also recommend using a short adaptor cable as opposed to some adaptor plug because trying to plug a larger connector into a smaller stepdown adaptor could potentially damage the headphone jack or interfere with where the recorder will be stored while recording.
Ok, at this point, you, my Good Pilot, are ready to rock. There’s just one little insignificant detail: WHO is going to record the audio while you’re busy piloting your platform? THIS may be the most important consideration to whether or not to use an all-in-one recorder or recorder with external mics.
If you’re a ‘guerrilla pilot’ like many people, you’re at best a crew of pilot and spotter. This means you can delegate the spotter to do double duty as audio engineer. With a little training and practice, your spotter can carry out the audio recording duties while spotting. Audio recording like this doesn’t require a B.Mus degree to be good, granted that the recordist has some practice.
If you’re a one-pilot operator, then you’ll need to consider an all-in-one solution and forget the external mics. What you’ll want to do is get a lightweight tri-leg mic stand or repurpose an old tripod lightstand or cheap old consumer camera tripod. Most recorders have a standard ¼” threaded hole on the bottom or side to allow the recorder to be attached to a camera tripod shoe. For a mic stand, there are adaptors that will mate the typical mic-stand thread to a ¼” adaptor for ease of use. I recommend a tripod-style mic stand because they’ll be more stable in a wider variety of environments than one of the cast-iron round base mic stands that are widely used.
Repurposing an old lightweight collapsible lightstand will require some sort of clamp-on adaptor to let you mount the recorder. In this era of smartphones, a little shopping around should yield a fastening solution, thanks to all the ingenious fastening systems available for smartphones and tablets. One nice thing about using clamp-on mounting brackets is they’ll tend to fit a broad variety of stands since they’re usually designed to attach to a broad range of stands.
Mounting the recorder to whatever stand you opt for means the entire stand/recorder setup can be carried with one hand, which is better for you and/or your spotter when out on production where time is important.
Where to purchase all this? First check out your local music superstore or independent music store that sells musical electronics. Their audio sales personnel may be of some help in getting you set up with a system that meets your requirements. Next is online, where there’s a wide variety of online stores vending gear if you know what you’re looking for. Nice thing about a ‘brick and mortar’ store is that sales staff may be able to answer your questions better than an online search or waiting to hear back from an online vendor’s helpdesk.
To recap, audio IS important for video – good audio can greatly enhance your already great video. Bad audio will destroy great video. Good audio can easily be acquired with a little practice and without impeding your workflow, whether in the field or in post. Just like learning how to drone, you’ll have to practice some, but if you’re used to the complexity of droning and drone cinematography, this is a skillset you’ll acquire easily. Happy Droning!
Jery Winters holds a degree in audio recording from the Johns Hopkins University