Audio Recorders

When it comes to audio recording, as with photography there are two primary types of recordings you will be concerned with. By far the simplest is the witness interview and event logging. It is helpful to record the witness testimony simply so you have a record of all that was said. It becomes much easier to review later; small details that might have otherwise been overlooked are there on the recording and can be included in your case files. Regarding event logging, some investigators do this, I do not. The reason is that while simpler than writing a log, it requires speaking while the investigation is underway. This could interfere with EVP recording in progress.

The type of recorder you use for this application is not really critical. Any inexpensive voice recorder will do nicely. One consideration might be ease of review. Since it is likely you will stop and start the recorder many times while reviewing the statement, it should be one which is easy to use in this manner. Another consideration is the overall sensitivity of the recorder to voice. There is no reason to use an extremely sensitive machine since in most cases you and the client are sitting down face to face discussing the case with the recorder right there too. A recorder which is too sensitive may pick up background noise which could make the recording difficult to understand.

By far the more complex recording issues become evident when you want to record actual evidence. Previously I would not recommend any digital recording system for this application, instead requiring the use of good quality analog cassette or reel to reel systems. Since many insist on using digital anyway, I recently conducted a series of tests using a high end digital recorder. This recorder allowed me to test various sample rates and evaluate the end result of each. It is beyond the scope of this report to make any recommendations for specific makes or models; however certain minimum specifications can be made that apply to all recorders.

First, all recordings, whether digital or analog should be made in stereo. The use of dual channels allows each to act as a check on the other. Any valid sound should be present on both channels. If one picks up a signal while the other gets nothing, the possibility exists that microphone placement may have been such that a stray EM Field may have been responsible. Another advantage is that the use of two channels will allow you to hear depth to your sound. You have two ears, and by using dual channel recording both can work together to determine not only the sound but its direction and to an extent its distance from you. It is much as if you were actually present as the sound was recorded.

The second concern that applies to all recorders is frequency response. While it may be desirable to use a certain amount of voice emphasis, it should not be the recorder that applies any filtering. The recorder should faithfully reproduce anything you send to it. For EVP work it is desirable that any recorder should reproduce all frequencies between 30 Hz up to 12 kHz. Recorders which exceed this are even better, but this is the minimum range the recorder should cover.

A final consideration when choosing a recorder is shielding. The recorder should be well shielded against outside interference. Older analog recorders are often placed in steel cases which provide excellent isolation. However the newer machines which are in plastic cases can also be shielded internally just as well. This is a matter of the design and must be considered when purchasing a recorder. It doesn't matter whether the shielding is the case or an internal shield, just as long as it's there. Most mid to high end recorders will meet the shielding requirements.

When it comes to Digital, many insist on using those little voice recorders for EVP recording. But before you do, Consider the limitations,

READ THIS FIRSTIt will give you the minimum acceptable standards your recorder should meet. If you happen to have a small portable that meets them, fine, use it. Otherwise your EVP will likely suffer from poor quality or not be suitable for in-depth analysis.

Any good quality microphone can be used for EVP work. There is some controversy regarding electret versus dynamic. My recommendation is to simply try both. Results have been obtained with both types.

The mixer is simply a standard audio mixer board such as used in small public address applications. The scenario described here uses a four channel version, which should do well in most applications. One important capability it requires is to be able to mix to a stereo output. (pan pots) Some smaller ones do not have this feature. Many also include bandpass filtering. If you choose to use a bandpass filter it should cover the range from 200 Hz to about 3 kHz. This is the range of normal human voice, male, female and children. If you want to be even more selective, you may use narrower pass bands. Voice is comprised of two components, vocal and fricatives. The fricatives are similar regardless of whether it is a child, a male, or a female voice. They are the sounds made by the tongue and teeth, "S", "T", and "K" are some examples. The pass band should be between 1.5 and 3 kHz. The vocal component differs somewhat. For a male voice, the recommended pass band is between 200 and 400 Hz, a female pass band would be 300 to 600 Hz. Children generally are between 350 to 700 Hz. The bandpass filter can be customized to whichever you are trying for, or simply use the wider 200 to 3 kHz range for all. The gain in performance of the wider band is noticeable, but not to a great degree.

Lastly, an area of controversy. Tapes may be new or reused, but only if they are bulk erased, not simply erased by the recorder. However ALL tapes, even new, should be bulk erased before use. There are residual fields left from the manufacturing process. Put a new unrecorded tape in a good quality stereo and turn the bass and the volume up. Hit play and listen for a "whomp, whomp" sound as the tape runs. Those are residual magnetic fields. They will cause false EVP when you combine them with the steady hiss you get in the field. Your recorder erase head will not eliminate all of them. For the same reason you can't completely erase a tape for reuse. The erase head and the record/play heads do not track perfectly. That is why, when you reuse a tape you can still hear a faint voice left from the previous recording, even though you recorded over it. The bulk eraser, properly used, will eliminate both problems since it erases the entire tape, not just the narrow bands where the previous audio was recorded. The bulk eraser will clean a used tape just as well as a new tape, so as long as the used tape is mechanically sound there is no reason it is any less desirable than a new tape. Use it.

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