What is sound?
Think of a piano. When you hit a key at the far right, you will get a note with a higher frequency than when you hit a key on the far left. Frequency, sometimes referred to as pitch, is the number of times per second that a sound pressure wave repeats itself. The units of frequency are called hertz (Hz). Humans with normal hearing can hear sounds between 20 Hz and 20,000 Hz.
Most “ears” are great at detecting sounds between around 200 Hz to 12000 Hz, but beyond that range they are less sensitive. A child with really good hearing may be able to hear sounds clearly up to around 16000 Hz, and “detect” sounds up to almost 20000 Hz. With age, hearing tends to become less acute, particularly for high frequencies, and for most adults the upper limit is usually around 16000 Hz. Frequencies above 20,000 Hz are known as ultrasound.
When your dog tilts her head to listen to seemingly imaginary sounds, she is tuning in to ultrasonic frequencies, as high as 45,000 Hz. You can see why dog whistles are so effective! Bats can hear at among the highest frequencies of any mammal, up to 120,000 Hz. They use ultrasonic vocalizations as sonar, allowing them to pursue tiny insects in the dark without bumping into objects.
At the other end of the spectrum are very low-frequency sounds (below 20 Hz), known as infrasound. Elephants use infrasound for communication, making sounds too low for humans to hear. Because low-frequency sounds travel farther than high-frequency ones, infrasound is ideal for communicating over long distances.
At the extreme low end, “ears” are not very good at hearing at all, but other parts of the body can detect the vibrations which the brain interprets as very low sound – thus for very low frequencies you not only hear with your ears, but with your whole body.
The intensity of sound is technically called “Sound Pressure Level” (SPL). Over the normal hearing range, SPL approximately correlates to “loudness” (how “loud” it sounds is the subjective sensation). In order to hear sounds in the extreme low-frequency range with your ears, the Sound Pressure Level needs to be so high that it is likely to cause permanent hearing damage.
To hear sounds down to 20 Hz, you really need some very large speakers that can move enough air so that your body can “hear” it. Of course, another option is to record the sound and enhance it during playback by using a program like Audacity (free, open-source program) or even just cranking up the volume. Using software is nice because you can remove ambient noise from your recording and concentrate on the EVP.
This is the relative strength of sound waves (transmitted vibrations), which we perceive as loudness or volume. Amplitude is measured in decibels (dB), which refer to the sound pressure level or intensity. The lower threshold of human hearing is 0 dB at 1kHz. Moderate levels of sound (a normal speaking voice, for example) are under 60 dB (a former boss of mine repeatedly clocked in at 75, however. Yes, I secretly measured him, and no, I no longer work there).
Relatively loud sounds, like that of a vacuum cleaner, measure around 70 dB. When workplace sound levels reach or exceed 85 dB, employers must provide hearing protection. A rock concert, at around 125 dB, is pushing the human pain threshold.
For some reason, it seems like a large percentage of EVPs are whispered words or phrases. There are definitely exceptions, but this does seem to be the way it often happens. Your guess is as good as anyone else’s as to why this might be the case. Are ghosts afraid of frightening us? Are they trying to remain hidden? Is there some sort of “ghost code” preventing them from being louder? And what about the ghosts who violate this observation? And where does music come from, which is sometimes heard when there is no obvious source?
I wish I had the answers. But I do know that regardless of the answers to these “why” questions…voices and noises are probably the most common evidence we get. Once you get used to listening closely, you will be amazed at the clarity of some of them. In the EVP section of this website, I keep an updated collection of EVPs from my own investigations, from “official” sources like police video, and from trusted colleagues. While I may occasionally include EVPs from unknown sources, they will be clearly marked.
I encourage you to get a decent audio recorder and visit some haunted locations to see what you get. You don’t need to spend a lot of money to do this, and it is really life-changing when you have your first voice capture!
Equipment: Any good quality sound recorder should work, but pay close attention to the microphone. If you use a built-in microphone, be sure it can pick up lower frequency sounds. An external mic is a preferred option, you just get better quality sound (and more of it). Behringer ECM8000 measurement microphone and a Roland R-26 field recorder are my recommendations if you are buying equipment specifically to capture EVPs.