5.7.1.1 Many collections are created through programs of field recording rather than, or perhaps in addition to, the acquisition and preservation transfer of historic recordings to stable digital storage formats and systems. These field recordings may be used in the creation of oral history collections, programs of traditional and other cultural performance, environment and wildlife recordings, or as part of the responsibility of broadcast collections. Regardless of the subject matter, where these recordings are destined for long term retention in archival collections it is most effective to make a decision about matters relating to their archival life at the time of planning the recording. In fact, inappropriate formats and technologies can severely limit the life and usability of the resultant audio.
5.7.1.2 Field recording may be undertaken in a variety of locations and situations, and the subject of such recording may be anything that makes a sound; from people, technology, plants or animals, to the environment itself. Recordings may be made to capture the acoustic context, i.e. in which the desired sound is recorded in an acoustic environment, or may be isolated from it, in which the recording technology may be deployed in a way which minimises the environment in which the recording is made. Recordings may be made in lounge chairs in big cities, on the verandas of remote bungalows, or where there is neither technology nor society to support it. The possibilities are virtually limitless and consequently this chapter on field recording technologies does not seek to discuss the specific discipline-related details of field recording techniques. Rather, it answers a simple question: "How do you best create a sound recording in the field in which the content is intended for long term archival storage?"
5.7.1.3 This subject of this section falls somewhat between the previous chapters on signal extraction, and the following chapters on digital storage technologies. It is included here, as it addresses the creation of digital audio content which is ingested into the digital storage systems as per the following chapters.
5.7.2.1 The same technical recording standards apply to field recordings as they do to archival transfers; i.e. they should be captured and stored in a widely used, standard linear audio file format, normally .wav or BWF .wav format; they should be created with a suitable sampling rate; at least 48 kHz, but, depending on intentions, possibly higher, either 96 kHz or maybe in some circumstances 192 kHz or higher. It is advisable to make recordings at 24 bit. Lower rates will not reflect the dynamic range of the performance and the environment in which the recording is made and could well result in low level signals of very poor quality.
5.7.2.2 Whatever the recording resolution, it is advisable to record natively to a standard format. This allows direct transfer to archival storage without alteration of the format and simplifies the archiving processes. Using BWF facilitates the collection of critical metadata which is necessary to the life cycle of archival digital information.
5.7.2.3 The use of data reduced (popularly called compressed) recording formats, such as MP3 or ATRAC encoding will produce recordings which do not meet archival standards. Data reduced formats, although highly developed, not only omit data irretrievably that would otherwise be captured by a non-data reduced format, but also create artefacts in the time domain as well as in the spectral domain. Such artefacts can lead to misinterpretations of spectral components as well as of time-related components, especially when analysing the signal by means of a spectral tool. The artefacts of data reduction codecs cannot be recalculated or compensated for at a post processing stage, as they are dependant on the level, dynamics and frequency spectrum of the original signal. For archival purposes it is advisable to re-encode the resultant files of compressed recording formats as .wav files (this is also the case with Minidisc,and early technology which used lossy codecs (See 5.6.10 Minidisc). While this does not replace the missing data, it does reduce further dependence on the codecs.
5.7.3.1 The decision about the use of a particular piece of recording equipment depends on many matters. There are, however, a number of technical issues common to all field recording situations and these can be grouped under three headings: archival compatibility, audio quality, and reliability.
5.7.3.2 Archival compatibility
5.7.3.2.1 The choice of the recording format in the digital domain has a long, and irreversible, impact on archival life: e.g. lossy compression formats may reduce particular usages. For this reason the recording device should be chosen according to the archival compatibility of its recording format. Current technology offers the possibility of recording directly to a file based format using hard disk and solid state recorders. Such devices usually provide a choice of several linear and data reduced recording formats. The selection of .wav or BWF .wav is recommended. Raw or proprietary formats should be avoided as these often have to be transferred to .wav or BWF .wav via proprietary software for future long term archiving. In keeping with archival recommendations, data reduced recording formats should not be used.
5.7.3.2.2 An alternative to dedicated portable recorders is a suitably equipped laptop computer. With the addition of a high quality microphone pre amp and analogue to digital convertor (see Section 2.4 Analogue to Digital Converters (A/D)) sound can be directly recorded to a laptop using widely available recording software. The same recommendations regarding file format applies to laptops as well, i.e. it is generally best to record directly in the storage format. This solution is practical, but high power consumption, as well as the acoustic noise which may be generated by the laptop itself, and the conspicuousness of the computer make this suitable for only some situations.
5.7.3.2.3 The laptop, and many of the portable recording devices, can be configured to record simultaneously to an external hard disk. This additional safety strategy is outlined in 5.7.5.1 (Transfer and Backup of content in the Field).
5.7.3.3 Audio quality
5.7.3.3.1 The audio quality should be chosen according to archival recommendations in Chapter 2, Key Digital Principles. The requirement for good quality recording applies to all types of content. Contrary to widespread opinion, spoken word recordings benefit from the same high resolution as music recordings, in fact it may be argued that the dynamics of speech places more demands on recording technology than many forms of music. In addition, if detailed signal analysis (e.g. formant / transient consonant analysis etc.) is required, the higher quality is a necessity.
5.7.3.4 Microphones
5.7.3.4.1 The discussion below regarding microphones is limited to issues related to the creation of archival recordings. Much more can be said about microphones as these are, in essence, the tools used in the most creative and manipulable part of the process and it is recommended that any field recordist be familiar with the use of microphones.
5.7.3.4.2 The use of external microphones, separate from the recorder, is recommended in the majority of recording situations. This minimises the inherent system noise captured by inbuilt microphones, and avoids handling noise when operating the recorder. The quality of the microphones should be sufficient to match the needs of the recording task as well as the specifications of the recording device, noting especially the signal to noise ratio (SNR). In order to capture the full dynamic range possible, and hence record 24 bit recordings, the use of good quality external microphones with a suitable preamplifier are necessary as most of the lower quality recording devices and microphones compromise at this crucial point.
5.7.3.4.3 In some recording situations the positional characteristics associated with the event are important. To capture such information a pair of external microphones deployed in a standard array is required (see Section 5.7.4.3 below). A standardised microphone array will provide comprehensible stereo sound characteristics whereas fixed internal microphones, as provided by many devices, usually do not match any standardised microphone array and are not manipulable. Condenser microphones are the most sensitive, and generally preferred for best recording results. Condenser microphones need phantom power which is normally provided by a professional recording device, (ideally switchable) but can also be provided by an external battery or mains powered supply. Condenser microphones tend to be more likely to be damaged in poor conditions and it may be preferable to trade off sensitivity and use more robust microphones such as dynamic microphones in some situations. Condensor microphones are also quite expensive, and very good results can be achieved with some of the higher quality electret-condenser microphones which, having a permanently charged capsule, can operate for extended periods of time on a small battery. Outdoor recording, especially with condenser or electret-condenser microphones, requires adequate high quality wind shields. Incorrect and ad hoc wind shields can be detrimental to the recording characteristics and alter the polar patterns of the microphones making the recording less predictable. Users should be aware of this effect when selecting and using windshields.
5.7.3.5 Reliability
5.7.3.5.1 Unreliable equipment has the potential to lose already recorded material or fail just when it is required for a recording. To minimise the risk of failure, recording equipment should be chosen to give the best possible reliability. Low cost consumer-grade devices are in many cases, flimsy and insubstantial, and easily subject to damage, and should not be used in the field before being extensively tested. In addition to more robust construction professional devices offer more reliable circuitry and interfaces, such as balanced microphone inputs, and so allow long cable runs and more reliable professional connectors. Even though low cost equipment is more likely to be susceptible to damage and failure, cost should only be an indicator of reliability and all field equipment should be tested extensively before being used in the field.
5.7.3.6 Testing and maintenance
5.7.3.6.1 Regardless of cost or quality, all recording equipment should be regularly tested and maintained to ensure accurate and reliable functionality especially under field conditions. The integrity of the recording system should be tested, especially after equipment has been dropped or transported under irregular conditions. The frequency response of microphones should be regularly measured to ensure they are functioning adequately. Dust and humidity protection is vital in keeping equipment in good working condition. Regular checking and cleaning of the devices, including connectors and other surfaces is vital to maintaining a reliable recording device. Equipment should be allowed to acclimatise to changing environmental conditions, especially when moved from a cool dry environment, such as a plane’s cargo hold, to a hot humid environment. All test results should be kept to allow the production of a continuous report of the maintenance condition of field equipment and to foresee necessary exchange of components.
5.7.3.7 Other considerations for field recording equipment
5.7.3.7.1 Though the technical specifications and characteristics help determine the quality and reliability of a recording device, other practical issues can impact on the choice of equipment according to the envisaged recording situation.Important features include;adequate recording time when battery-supplied; a rugged and clear design; easy handling; and a small and light-weighted but robust construction. Illuminated controls are essential for recording in the dark but result in higher battery consumption. A decision should be made as to whether the recording situation makes devices with changeable media (such as Flash or SD cards) or a back up hard disk preferable to enable a suitable safety strategy (see Section 5.7.5 Transfer and Backup of content in the Field). Ideally the device should allow fast and simple data transfer and duplication, and have an inconspicuous design (the latter of which reduces the visual impact on a documentary recording, and may also minimise the risk of theft).
5.7.4.1 The purpose of the recording and the rules of the particular discipline to which it belongs will govern many aspects of recording approaches, microphone techniques and the like. There are, however, a number of common concerns in making such a recording.
5.7.4.2 Field recordings usually record or document a given situation and under these circumstances the original dynamics of the documented action should be respected in the recording as well. Audio input levelling should orientate on the wanted signal, and not the general background noise, and continuous adjustment of the level during a recording should be done judiciously, if at all. Use of automatic gain control functions is not recommended as such features falsify original dynamics by raising low level parts (and therefore noise) and reducing the wanted signal dynamics. Likewise any limiters used in a recording should be applied cautiously. A well adjusted limiter will rescue the recording if an unexpected high level signal is captured but have absolutely no impact on the majority of the recording because it is not triggered by the level of the recording. On the other hand, a poorly adjusted limiter may simulate a perfect level on the meters of the recording device while the microphone itself may already be overloaded due to the input signal.Whenever possible, manual levelling is to be preferred and any limiter, adjusted so as it has no impact on the normal signal, only switched in after an optimum level has been achieved.
5.7.4.3 When making a recording where the signal is embedded in a noisy environment advantages are to be found in using standard stereo microphone arrays. There are many approaches but those that are briefly discussed here include near-coincident technique of which ORTF (Office de Radiodiffusion Télévision Francaise) is an example, XY crossed pair,AB parallel pair and MS (Mid-Side) techniques.
5.7.4.4 ORTF seems to be most useful where analysis and evaluation properties of the documentary recording are an important requirement. In this technique the microphone capsules are separated by 17cm at an angle of 110º. An ORTF recording, when analysed via headphones, enhance the ear and brain’s ability to trace a wanted signal within a noisy surrounding; the so called “cocktail party effect”. The head-related binaural microphone array imparts the extra information and so helps identifying wanted signals in noisy sound fields. Also, as the specification for ORTF is defined, the microphone set-up can be much more easily replicated in a standard way.
5.7.4.5 Standard XY crossed pairs are arranged so that the microphone capsules are as close together as possible, but pointing at least 90º away from each other. The intensity of the signal information is recorded, but ideally no phase difference is noted. This technique produces a recording that reproduces well on speakers, but does not have as much separation information as other techniques. AB parallel pair uses two omni-directional microphones in parallel separated by around 50cm. This technique has been favoured in very good acoustic environments but will rarely produce acceptable results in very noisy environments. It may have phase cancellation problems when summed to mono.
5.7.4.6 MS (Mid-Side) technique places a bidirectional microphone (figure 8) at right angles to the sound source, and a cardioid pick up pattern microphone (or sometime an omni directional microphone) pointing at the sound source. The two recorded signal may then be manipulated to produce mono compatible stereo recording (M+S, M-S). If recorded as MS information, the signal may also be manipulated after the event, and so gain some control over the apparent spread of microphones.
5.7.4.7 Some situations, where the exact nature of the event is unknown prior to the recording being made, can take advantage of movable directional microphones, multi-microphone techniques and multi¡track recording. Interviews may use two microphones pointed at the participating individuals, which presents very acceptable recordings. Clip microphones are, in many cases, less useful, as they pick up unwanted noise from body movements, breathing, clothing and jewellery, and record little or no information about the environment in which the recording was made, which is often an integral and necessary part of the field recording.
5.7.4.8 Microphone techniques contribute to the quality of the recorded content and this very brief consideration of them is only a guide to the possibilities. It is recommended that all those intending to make recordings in the field should become familiar with the possibilities afforded by good microphone techniques before making important recordings.
5.7.5.1 Field recordings remain vulnerable while in the field, and unless back up copies are created, are at risk of being lost. A second copy of a field recording should be made at the time of recording or as soon as possible after the recording is completed. Different workflows and situations make for different approaches, but generally speaking, the workflow selected should offer the best possible safety strategy.
5.7.5.2 Hard disk and solid state recorders offer a file based recording technology either on hard disks or on changeable card media. The recording is generally deleted from either of these media after the wanted file is transferred to another storage environment. This is clearly an area of risk in the use of the new technology and must be managed carefully to ensure no loss of wanted material. The recording medium should be regarded as an original carrier as long as possible. It should be erased only after verifying the correct data transfer into an archival system. In the case where a long field trip requires the management of large amounts of data which cannot be immediately archived, duplicates should be created and stored in the field. In the case of flash card or SD recorders it may be useful to invest in additional storage cards which are used to store recording until recorded content is transferred to a more sustainable storage system. In the case of hard disk or laptop recording devices, portable hard disk storage devices can be used to create backup copies until the data has been successfully transferred.
5.7.5.3 In practice, some devices offer parallel use of internal hard disk and storage cards, or allow the parallel recording to hard disk. This is an advantage as it enables the automatic creation of a safety copy as part of the recording process and should be undertaken whenever possible. Alternately, safety copies can be manually created in the field, using external hard disks, laptops or at least CD/ DVD drives.
5.7.5.4 Some devices create file names automatically when a new storage medium is inserted (automated numbering starting with the same file name on each new medium), so the copy process has to be carefully managed to be sure that files named the same on different carriers can be correctly matched with the correspondent metadata/ field notes etc. In the worst case this can lead to accidental erasure of identically named files and so a careful structure and naming strategy is necessary. Renaming the files after the copy process is recommended, provided that the original file is not changed or manipulated in some other way.
5.7.6.1 The absence of metadata describing the field recording, its context and related rights, severely limits the value of the recording. The lack of metadata (including preservation metadata) can have serious implications not only for ingestion into a repository, but also for subsequent archival management and dissemination of archival information. This data is so significant that its lack may lead an archives manager to reject the content. There is also critical technical and preservation information necessary to acquiring field recordings which should be obtained at the time of recording and included in the archival record. These include:
5.7.6.1.1 Recording device: Brand, model number, description of dynamically made adjustments during the course of the recording, recording level, recording format, encoding (not recommended but should circumstances require its use, it must be documented).
5.7.6.1.2 Microphones: microphone types/ polar pattern, information about the microphone array, distance, special approach (like clip microphones, analytic multi microphone technique etc).
5.7.6.1.3 Use of additional equipment such as windshields etc. description of room situation, etc.
5.7.6.1.4 Carrier: type, specifications of original carrier (flash card, disk etc) or hard disk.
5.7.6.1.5 Power source: batteries, 50 or 60 Hz AC, unstable or fluctuating power conditions, etc.
5.7.7.1 Field recordings exist in relation to each other and to other events, objects and information. Developments in the research communities are leading towards integrated data and metadata acquisition tools which document and relate different objects and the times and place in which they were created.Various international projects meanwhile have created tools that meet the requirements of specific metadata schemes. Such tools offer a relatively complete metadata collection and make transfer to established database systems easier and ensure accurate data for future researchers. At the time of writing such tools and concepts are in an early stage of development, they also tend to contain data that is discipline specific and so are not discussed here, however, it is important that all the technical data described above is acquired for populating future management and access systems. All data acquired should have in mind the transfer compatibility to the final archiving system. Until standards come into being, use of UNICODE characters and XML format is recommended.
5.7.7.2 If metadata is collected manually, without using acquisition tools as mentioned above, it is recommended to use a format that can easily be transferred to usual database structures. Alternatively, institutes and archives sometimes provide their individual tools and if possible these should be used in the field.
5.7.8.1 The time required to record an important event or interview can be quite extensive. The time required to preserve a field recording can be reduced to the time it takes to ingest the data and metadata if the field recording approach has been designed properly. If the system depends on manual approaches it is quite likely that much valuable information will be lost due to human error, or lack of resources to undertake this time consuming, but important, archival task.