Field Recording Tips

Last updated February 2007.

Record Digitally

You will want to get your recording into digital format eventually, so you'd might as well make it digital from the outset. Almost any use that you will make of the recording, including transcription, editing, and acoustic analysis, will best be done on a digital version. Furthermore,archiving of your recording is best done digitally. A digital recording can be copied more rapidly than an analog recording can be, and more importantly, it can be copied repeatedly without degradation.

Record Uncompressed

Audio data can be recorded uncompressed (that is, in what is known as linear Pulse Code Modulated format) or using a variety of kinds of compression. The widely used audio compression techniques, such as MP3, are all lossy compression techniques. That is, they distort the signal. For research purposes, it is best to minimize distortion. You should therefore record initially speech without compression. See Saving Space Without Distortion for some distortion-free ways of saving space.

Note that it is important to distinguish between the format of the audio data itself and the file format. The .wav format, for example, is a file format, not a data format. A .wav file may contain a variety of different data formats, so just knowing that something is in ".wav format" does not tell you what format the data is in. For an explanation of audio file and data formats, see Lecture Notes on Audio Formats.

Resolution

Virtually all current digitizers and digital recorders provide 16 bit resolution. This is perfectly adequate for linguistic purposes. Old 8 bit digitizers, such as found on personal computers prior to the mid-1990s, should be avoided. Some current devices offer resolution higher than 16 bits. This is not really necessary, and much existing software cannot deal with resolutions higher than 16 bits, so in general it is best to stick with 16 bits.

Sampling Rate

Many devices record by default at the CD sampling rate of 44,100 samples per second. This corresponds to a frequency range of about 20,000 Hz. Most adults have limited or no hearing in the upper part of this range. In any case, all of the linguistic information in speech is located below 8,000 Hz. A sampling rate of around 20,000 samples per second is therefore more than adequate for linguistic purposes. A sampling rate of 22,050 samples per second, half the CD rate, is available on most digital recorders and digitizers. A discussion of the choice of sampling rate can be found here.

Recommendations

Best

Flash Card Recorders

Flash card recorders record digitally on removable semiconductor memory of the same sort used by digital cameras. Flash cards are therefore fairly inexpensive and widely available. They can be read by virtually any computer without special software since they can be mounted as a file system. If the computer does not have a built in flash card reader, an external reader that attaches to a USB port can be had quite cheaply. Good flash card recorders, such as the Marantz PMD670, record uncompressed, with a choice of sampling rates, have microphone inputs, and provide input level meters.

PCMCIA Disk Recorders

PCMCIA disk recorders, such as the Sonifex Courier, are similar to flash card recorders but use very thin hard drives that are inserted into a PCMCIA slot. PCMCIA hard drives also mount as filesystems and so do not require special software. If your computer does not have a PCMCIA slot, as most desktop computers do not, it is necessary either to buy an external PCMCIA card reader or to transfer your data via a laptop (since most laptops have a PCMCIA slot). PCMCIA disk recorders are therefore somewhat less convenient than flash card recorders.

Second Best

Digital Audio Tape Recorders

DATs produce a high quality recording but have a number of disadvantages in comparison to more recent devices. First, they have short battery life in comparison with devices that use media such as flash memory, PCMCIA cards, or minidiscs. This can be a real disadvantage in a field setting. Second, they are generally more expensive than other comparable digital recorders. Third, the tapes on which they record are subject to melting and other physical damage. Finally, they often require a special interface for uploading data to a computer.

Minidisc Recorders

Minidisc recorders have the advantages of being small, cheap, and using cheap, removable media. A minidisc that holds two hours of mono costs about US$1.One disadvantage is that they use a lossy compression technique called ATRAC. ATRAC compression does not cause as much distortion as MP3 compression, so minidisc recordings are usable for most linguistic purposes, including much acoustic phonetic work.However, it is possible that minidisc recordings are not desirable for some kinds of acoustic analysis, such as spectral analysis of weak fricatives and stop bursts. One study has shown no effect of ATRAC compression on measurements of vowel formants.

One problem with portable minidisc recorders is that they are so small that manipulating the controls can be difficult, especially when it is desired to change settings while working with an informant. Another issue is that many portable models do not have digital output, so it is necessary to use an additional desktop model to upload the data to a computer.

HiMD Recorders

There is now a new kind of minidisc recorder called HiMD. Unlike regular MD recorders, these provide the choice of ATRAC compression and uncompressed recording. However, like regular minidisc recorders, the portable models generally do not provide digital output.

Discouraged

Cassette Recorders

The better portable cassette recorders, such as the Sony Walkman Professional and the Sony TCM-5000 in their day produced fairly high quality recordings. Nowadays, however, there is really no reason to use analog recorders. For the reasons mentioned above, digital recording is generally better. Furthermore, cassettes are not terribly robust. They can be melted by the heat of the sun and are subject to physical wear and tear.

Pocket Recorders

There are a number of very small digital recorders available, intended primarily for dictating voice memos. These are very convenient as they fit in a shirt pocket, and may be useful if you want to be able to record impromptu or unobtrusively. However, they have a number of disadvantages that make them undesirable for other research purposes.First and foremost, most if not all such devices record a relatively narrow frequency band and use lossy compression in order to pack as much speech as possible into a small amount of memory. As a result, the acoustic quality leaves much to be desired. It may be possible to understand the recording, but it will very likely not be suitable for acoustic analysis and transcription of nuances may be problematic. Secondly, many such devices record on non-removable memory. In this case, you must upload the contents to a computer before you can record more. Third, they often have only a built-in microphone of not particularly high quality and lack a microphone input jack.

Music Players

A number of devices intended primarily for playing back music allow for recording. These include the Nomad Jukebox and the Applie iPod.These generally have two disadvantages that make them unsuitable for linguistic research. First, they have no input level meter. This makes it very difficult to set suitable input levels, resulting either in overloading and clipping or unnecessarily low volume levels. Secondly, some of them record only in MP3 format. Furthermore, some of them do not accept microphone level input. They require line-level input, which makes it necessary to use an external preamplifier. This is cumbersome and may add noise. An additional problem is that they use a special filesystem, so special purpose software is generally necessary to upload files from them. This software is usually available only for Microsoft and Apple operating systems.