This guide is split into many parts and is intended to fill a gap left by the numerous field recording blogs and websites. Many of these sites make quality audio files available for both the general public and novice alike, to either listen to for pleasure, or where provided with a description of technique and equipment used, act as useful reference material for the novice recordist. Unfortunately, audio material of instructional value for the beginner tends to be unavailable in this format, being limited to text-book reference material only. This can result in the beginner being unaware of common problems, their failure to recognise faults and inability to rectify them when they occur. This limits progress and development towards the production of better quality recordings.
Unbeknown to the beginner, there can also be a detrimental side effect to this wealth and availability of quality field recording material, as it may well encourage the setting of targets which are far too high for the beginners’ limited experience both out in the field, and later back home during the conversion process from raw audio to the desired final format.
Understandably, most experienced field recordists are reluctant to admit to having failures, least of all posting them on the internet for everyone to hear. The problem therefore is the lack of suitable material from which the novice can learn about the problems, faults and their causes. Without that knowledge, the learning curve will be that much more difficult and faults will keep popping up unannounced during subsequent field recording and post production sessions, causing frustration and increasing the likelihood of the novice simply abandoning the hobby.
In this first part we consider a few of the many common problems encountered, together with the best methods of dealing with them:-
Wind
This is one of the most common of all the problems to be encountered which often confuses the novice, mainly due to the belief that the foam covers supplied with their newly purchased recorder or microphone are suitable for the task – they are not; they are totally unsuitable for field recording.
These are the effects heard as a result of insufficient wind protection. The rumbling sound heard cannot be effectively removed in post-processing without seriously affecting the audio quality of the recording:
Garden Ambience, Diss Norfolk. Recorded 21 May 2008 19:09hrs. Mid-side stereo array Rode NT1A & NT2A(Fig. 8 pattern) microphones fed direct to Edirol R-4 recorder. Original 44.1KHz, 16Bit, 2-channel.
The solution is simply to provide satisfactory wind protection to the microphones in the form of a suitable windjammer, often termed ‘dead kitten’ for use in low velocity winds. In the case of more higher velocity winds and more extreme conditions, a blimp system may be used which not only provides greater protection against direct wind blow, but also isolates the microphones from wind buffet and handling noise from the supporting structure (including the hand); by supporting them in an elasticated suspension system within the blimp. Where unusual microphone arrays are deployed, it is sometimes better to homebrew your own system to suit the particular array as shown here with the basket blimp.
Handling Noise
Most beginners sensibly make a start with the smaller handheld or portable recorders, making use of the recorder’s own in-built microphone system. Although much can be said for the portability and extremely high audio quality of the current models to be produced, they all tend to have an inherent problem of being susceptible to the slightest re-positioning or movement within the hand or operation of controls whilst recording is in progress. This is due to the manufacturing difficulty in providing suitable isolation between the microphone elements and recorder controls and casing. I must stress that handling noise is not limited to portable or handheld recorders, in fact it is encountered with external microphones as well – they all tend to pick up handling noise, some more than others. As an example the following audio, despite being protected within a sophisticated suspension cradle still picks up handling noise.
Walking Through Dry Grass. Recorded 03 June 2010. 14:36hrs. Rode NT4 XY microphone in blimp system mounted on monopod. SD702 recorder. Original 48KHz, 24 Bit.
The only way to be 99.99% certain of avoiding handling noise is by not touching or moving the microphone system whilst recording, that means laying it down somewhere or mounting it on a tripod. If you must hand-hold the microphone and cannot afford the expense of extra equipment then at least provide some form of isolation such as wearing a glove or wrapping faux-fur around its barrel. Where portability is required whilst recording, such as in the recording above, then a shock-mount, sometimes termed a cat’s-cradle will be required, or better still one already incorporated in a blimp suspension system as shown above. If you are wondering why the mention of 99.99% certainty; that is because vibrational noise can even be induced by wind and traffic into a tripod mounted microphone.
Power Supplies
The Scout motto immediately springs to mind here – Be Prepared, although not quite as all-encompassing as their motto; nevertheless, the field recordist should always be prepared with respect to recorder, preamplifier and microphone power supplies, in particular their failure. There is nothing more dispiriting than making that special field recording trip out only to be thwarted by a last-minute failure in power supply. The consequences could be that much worse if failure occurs part-way through a digital recording, resulting in the corruption and complete loss of memory with some recorders – be warned! Removable batteries pose the least problem, just remember to take plenty of useable spares. In-built batteries are more unpredictable and have the habit of just failing at the most inappropriate moment. Make certain their charge is maintained and continually monitored, even when not in use. Last of all, if you rely on battery-powered microphones rather than plug-in, or phantom power supplied from other sources, make sure you carry spares for those as well.
Sorry, but no audio recording sample for this – it just drops out!
Clipping & Distortion
Keeping it simple – clipping is caused by overdriving the recorder’s amplifier stage beyond its handling capability. This results in the louder portions of a signal being truncated, producing distortion of the audio signal.
Digital amplifiers work best and at lower levels of self-noise, when operated at high gain levels; the aim therefore is to record with gain levels set as high as possible without exceeding 0dBFS. Fortunately most digital recorders possess a limit or clipping indicator which flashes whenever the manufacture’s preset recording limit is breached. The safest method of operation is to keep your eye on the recording level meter and lower the recorder gain setting if clipping is indicated; failing that, the recorded audio is likely to be distorted, the ‘take’ lost, and your time wasted. There are post-processing computer programs capable of repairing marginally clipped files, but as with most post-processing, audio quality is lost. This loss of quality can be quite noticeable where clipping repair work has been carried out and often results in a recording having limited dynamic range.
Setting correct recording levels is one of the more difficult aspects of field recording, often being dependant upon the predictability of the sound source and whether or not there will be further opportunity for repeat ‘takes’.
Where the recording is a ‘one-shot take’ with no opportunity for preliminary test recordings, there is a need to err on the side of caution when it comes to setting levels. However, there are some useful tricks of the trade available in order to help reduce noise by maximizing recorder gain levels and at the same time reduce the likelihood of clipping. This will be discussed in a subsequent part of the guide.
Watton High Street. Recorded 28 September 2011 16:07hrs. Soundman Classic OKMII with A3 adapter mounted in spectacle case fed to Olympus LS-11. Original 48KHz, 24 Bit.
In the above sample the recorder gain levels were set for the ambient traffic noise with enough caution built in to satisfactorily record most unexpected sounds as well, without clipping, such as the nearby motorcycle alarm encountered. However, as with most things in life, an element of luck tends to be involved in field recording; unfortunately this luck has a habit of running out at the most inopportune moment, as was the case here, when the loudest of all vehicles roared off down the street, resulting in quite severe clipping and distortion in the recording. In fact the recording is so badly distorted that it’s impossible to determine whether it was a motorcycle or some other type of vehicle.
Screenshot of the recording, with clipped area indicated by arrows.
Faulty Cables & Connectors
These faults can be some of the most frustrating to deal with as they have a habit of occurring at a critical point in the recording session, or when time is at a premium.
For the beginner, possibly dealing with shorter lengths of cabling and just a few connectors, the problem tends to occur less frequent than at a more advanced level when dealing with multi-channel recorders and cable lengths of 10m or more. These longer cables tend to be more prone to damage both out in the field or when packing and unpacking the equipment.
One of the main causes of cable failure, apart from being chopped in two by a sharp object, is due to repeated incorrect coiling and uncoiling between recording sessions. I have included a very useful video below, which demonstrates the correct manner in which cables should be coiled.
There are other reasons for cable failure in addition to mechanical strain, such as the breakdown of its dielectric insulation. This damage is less common, so will not be considered here.
Cable failure can also occur at its junction with the connector, often caused through incorrectly fitted strain clamps, poor soldering, shorting inside the connector between adjacent tabs, or through stray wire filaments etc.
So let’s hear a typical cable failure:
USAF Refuelling Tanker Landing USAF Mildenhall, Suffolk UK. Recorded 14 May 2010. 10:14hrs. Rode NT1A & NT2A (Fig 8 pattern) mid-side stereo array mounted on tripod with faux-fur windjammers fed via 10m XLR cables to Edirol R-4 recorder inside vehicle.
The cable failure was in the signal feed from the Rode NT2A (Fig 8 pattern) microphone serving the side channel 2. It progressively becomes worse and fails completely towards the end of the recording.
This colour coded text has been bookmarked for more detailed consideration later on in the guide, once the principles of recording are more fully understood.
Slideshow
Wow, I enjoyed this entry. I will keep it handy for future use.
thank you,
Andrea