This is a beginner-level introduction to EMF field recording. Suppose you have not followed the Soldering EMF Tentacles Workshop. In that case, you may build your own stereo EMF detector from an open-source, free circuit Elektrosluch: electromagnetic wave detector published by Jonáš Gruska or buy it from LOM Audio whenever they restock them.
The device detects electromagnetic waves as the voltage difference in coils changes. The voltage varies with the distance between the transmitter and receiver coil and the transmitter signal frequency. Conductive materials give a significant voltage difference ranging between 0 and 0.072 volts. Our device’s integrated circuit (IC) contains two operational amplifiers (Op-Amp) that amplify the received voltage from coils. The voltage translates to digital audio frequencies in our recording device. However, the device does not measure the frequency range or the intensity of electromagnetic waves in numerical terms, as the coil is a quasi-sensor, not an actual sensor. For that, you would have to have at least an amateur measuring device that detects:
- Low-frequency electromagnetic field strength
- Electric field measurement
- Radio-frequency field strength monitoring
Scientific laboratories use arrays of EMF probes connected to an oscilloscope that provides a focused measurement of material properties, for example, oxides in metals. For precise measurements, they also conduct a series of calculations starting from the most straightforward equation for wavelength λ = c/f (wavelength is the speed of light divided by frequency). Rather than measurement, we are interested in the movement, in poetic and experiential qualities of electromagnetism.
Non-ionising electromagnetic frequency range
We are looking for devices that emit electromagnetic waves in different frequency ranges that vary in time. However, electrical devices are not the only sources of EM waves on Earth. A telluric, or Earth current, is an extremely low-frequency current that moves underground and results from natural causes and human activity. The strongest are geomagnetical currents induced by changes in the outer part of the Earth’s magnetic field. Interactions between the solar wind and the magnetosphere or solar radiation effects on the ionosphere usually cause them.
Electromagnetic radiation in our environment causes some concern regarding its effect on biotic organisms. Current studies show their impact is closely related to exposure duration, frequency, and intensity. Therefore, strict exposure regulation and citizens’ understanding of risks are paramount.
Low-frequency EM (lower than 100 kHz) is induced by alternating current and voltage in electricity production, transmission, and consumption. Sources of low-frequency EMS are power lines, electrical wiring, generators in power plants, transformer stations, electric motors, household appliances and many devices in the industry. Low-frequency EM has electrical and magnetic components. Electric fields are strong near high-voltage power lines, and magnetic fields near household appliances, induction hobs and welding machines. In areas accessible to humans, exposure to low-frequency EM is much lower than the limit values. If people walk directly under a high-voltage power line, exposure to these fields is relatively high but within the recommended values. Exposure to high-voltage power lines for a longer duration is not recommended. Low-voltage power lines cause much less exposure, and underground power lines have almost none.
High-frequency EM, ranging from 100 kHz to 300 GHz, has many applications in modern communications (mobile phones, wireless networks, Bluetooth devices, wireless mice, keyboards, cameras, babysitters, toys, and various security systems). There is yet insufficient scientific data that would confirm or reject the link between the emissions of these devices and health. It is recommended to know the sources of HF EM radiation in our environment and behave cautiously. For example, we never cover the receiver of our mobile device as radiation increases with decreased reception. As you will observe with your EMF detector, the field strength of EM decreases rapidly with distance. Most people are exposed to only a tiny fraction of the maximum recommended limit value, but it is always safer not to use a laptop as a pillow. Limit values may be exceeded in some workplaces (telecommunications, industry, medical care) and require special regulations. The wavelengths of AM radio signals vary from a maximum of 555 meters at 540 kHz, to a minimum of 176 meters at 1.700 MHz.
In contrast, radiation exposure in our living environment is usually far below the threshold at which potential health effects have been identified and substantiated. In medicine, powerful high-frequency EM is used to warm body tissue. These can relieve pain or destroy cancer cells. Such fields are also used to produce images of the brain or other body parts using magnetic resonance imaging (MR). Exposure of patients or medical staff may exceed normal safety thresholds. (Source: Institute for Nonionising Radiation, http://www.inis.si/)
- Low frequencies: Extremely Low Frequency (ELF) 3 Hz – 30 Hz;
- Super Low Frequency (SLF) 30 Hz –300 Hz;
- Ultra-Low Frequency (ULF) 300 Hz – 3 kHz;
- Very Low Frequency (VLF) 3 kHz – 30 kHz
- Radio: Low Frequency (LF) 30 kHz – 300 kHz;
- Medium Frequency (MF) 300 kHz – 3 MHz;
- High Frequency (HF) 3 MHz – 30 MHz;
- Very High Frequency (VHF) 30 MHz – 300 MHz / 10–1 millimetre
- Microwave: Ultra-High Frequency (UHF) 300 MHz – 3 GHz;
- Super High Frequency (SHF) 3 GHz – 30 GHz;
- Extremely High Frequency (EHF) 30 GHz – 300 GHz
- Far Infra Red (FIR) 300 GHz – 3 THz
- Visible light: Mid Infra-Red (MIR) 3 THz – 30 THz / 400 to 700 nanometre;
- Near Ultra Violet (NIR) 30 THz – 300 THz
- Near Ultra Violet, visible (NUV) 300 THz – 3 PHz
Ionising electromagnetic frequency range
- Extreme Ultra Violet (EUV) 3 PHz – 300 PHz
- Soft X-ray (SX) 300 PHz – 3 EHz
- Hard X-ray (HX) 3 EHz – 30 EHz
- Gamma Rays (Y) 30 EHz – 300 EHz
Ionising radiation is caused by subatomic electromagnetic particles with sufficient energy to change the atoms by detaching electrons. Ionising radiation is used in various fields, such as medicine, nuclear power, research, and industrial manufacturing. Still, it presents a potential health hazard if proper measures against exposure are not taken. Exposure to ionising radiation causes cell damage relative to the time and frequency of exposure, intensity and shielding from the exposure. The most prevalent damage to living tissue is ultraviolet radiation. The boundary between ionising and non-ionising radiation in the ultraviolet frequencies is not sharply defined because different atoms ionise at different energies. Unlike other electromagnetic waves, the subatomic particles travel at a speed that is 1% greater than that of light. Ionising subatomic particles include alpha, beta, and gamma particles. This type of radiation can penetrate the most common substances, including metals. The only substances that can absorb this radiation are thick lead and concrete.
Audio frequency range
We measure audio and EM frequencies in Hertz. However, they are very different physical phenomena. Sound needs particles of air to travel through space. Essentially sound is a vibration of molecules. When speaking about audio, we consider frequencies perceived by the human ear. However, animals and plants have a much different reception spectrum, but we will not address those here, although this field is intriguing for sound ecologists and field recordists alike. Humans start tactilely perceiving sound from a sub-sonic, i.e. infrasonic range of about 10 Hz. We begin to hear sound with our ears, not just by vibration, at about 20 Hz. Physical vibrating properties are significant in the low-frequency audio spectrum ranging from 20–250 Hz. We get such low frequencies when listening to EMF with some induction hobs.
Low frequencies sound softer, grounding and quieter to the human ear. At the same time, in psychoacoustics, they have the property of masking. That means that not enough low frequencies will make our sound sharp and tiring to the ear, while too dense low frequencies will blur the definition and clarity of other frequencies. Our ears have evolved to hear best in the mid-range audio frequencies from 250–4.000 Hz. Human speech and most of our main acoustic instruments are in this range. We find it abundant in field recording with EMF detectors, from sources such as computer monitors, plugs, lights or phones… High frequencies range from 4.000–20.000 Hz. In music, we primarily use the lower and mid-high range till about 10 kHz as higher frequencies mostly become very quiet; to young people, they are often very disturbing, and to older people, they are entirely silent due to gradual old-age hearing loss. We find high-range frequencies in public transportation, wi-fi routers, and electrical transformers.
A more detailed division of audible frequencies:
- sub-bass (10 Hz to 80 Hz),
- low (from 80 Hz to 200 Hz),
- low middle (from 200 Hz to 500 Hz),
- middle (from 500 Hz to 1200 Hz),
- upper-middle (from 1200 Hz to 2400 Hz),
- lower-high (from 2400 Hz to 4800 Hz),
- medium-high (from 4800 Hz to 9600 Hz),
- upper high (from 9600 Hz to 30000 Hz).
Other qualities of sound that we are listening for when recording with EMF detectors are:
- pulsating and rhythmical sounds like that of the electric meter,
- changes in pitch or glissandi like that of turning a device on and off or a machine acceleration,
- textures and different qualities of noises (white, pink, brown, grey), such as those found in computer servers.
Examples of raw EMF recordings
Artistic practices and electromagnetic frequencies
- Christina Kubisch, Electrical Walks.
- Paloma Kop, Electromagnetic Earth, series.
- Listen to Sensing Electromagnetics compilation published by Zvukolom.
- Adomas Palekas and Greta Galiauskaitė, Antennae, performance.
- beepblip, Morphoiki, upcoming album, August 2023
Methods of field recordings with EMF
Walking: The most crucial method is observation. Using an EMF detector, you will walk into a virtual acoustic space that makes you hear the inaudible world around us. Essentially, what we are doing, is having our electromagnetic walk around the city. An excellent source of EMF can be interior spaces, especially public transportation, computerised offices, stores, media-art exhibitions and homes with household equipment. As mentioned in the introduction video to Kubisch’s body of work, each city has a particular electromagnetic smog footprint. Exciting sites are also near the high-voltage power grid (see Anthropic Frequencies).
Stereo picture: As the detector has two coils and a stereo jack output, we can capture a stereo-panned image immediately in the field. Try and play with turning the device slowly or quickly around its axis. In this way, you will record a moving spatial sound and will not need automation in postproduction.
Make notes: It is essential to remember the tracks that sounded particularly interesting to you. You may take notes or remember the consecutive number of a significant recording. It will make your indexing and selecting work at the end of the recording session much faster and easier.
Duration: The duration of one take may vary from the nature of the sound you found and the purpose for which you will use it. We aim to record one whole sequence. As we have heard in the raw recording example of Underground Acceleration NYC 2013, this sequence was about 6 minutes, while in the neon lights installation Electromagnetic Beauty, the recording was just 2 minutes. After we estimate that the sequence has ended, we stop and thus store the recording.
Safety: Remember to press the Record button. It happens a lot. Also, take special care of your ears. Never record in gain that would be too loud, and keep your headphones on volume low.
Inputs and outputs
Some simpler recording devices only have one 3.5 jack input for the mic and line. It is not optimal, as line inputs have stronger signals than mic inputs. In terms of voltage, line-level signals are much stronger than mic input. Our device is a line input; we should use the former when we have a recorder that distinguishes between line and mic. Our detector has two inductors, each with its Op-Amp connected to the 2134 integrated circuit (IC) and a stereo jack, which gives us the possibility to record a stereo recording in which the left and right channels are distinct and reflect the difference in the electromagnetic wave propagation in our environment. To utilise this feature, we should not connect this device to a mono input but always use a stereo line input. We use headphones plugged into the recorder’s headphone output to listen to our EMF detector. Be careful not to set it too loud, which might damage your hearing.
Gain and volume
Understanding gain, particularly the difference between gain and volume, is essential to good field recording. Gain is the input signal that is detected by a device. It measures the amplitude with which the device (an audio recorder) receives a line input. In acoustics, a maximal gain is at 0db (decibels). Any input signal that exceeds the 0db threshold registers as sound distortion, also known as clipping. If we wish to produce a crunchy and distorted sound, we should always do that in postproduction in our DAW with overdrive in VSTs. We should never do it with line input as this is not so great for our device or hearing. To preserve the signal dynamics of the recording, an optimal average gain range is between -24db and -18db, and an optimal maximum gain is between -12db and -6db. This convention aims to create a balanced recording that will produce a similar output when we play it back on any device, such as studio speakers, car radios, mobile devices, pads, computers, and concert hall PAs. Most simple recorders have three levels of gain: low, mid, and high, and we set it with a knob on the device. Better recorders have a gain range from 0 to 100. We should begin recording monitoring at about 35 or lower. We usually set the gain in such devices in the menu in recording settings. In the best recorders, we may charge the gain in decibels. We should begin our recording monitoring at about -18db. We should not exceed these values as we risk distortion or production of recorder noise (at 50Hz).
The picture with three tracks of the same recording shows a gain that is too low in the first track and will produce a hiss in our recording if we wish to normalise it; a gain that is optimal in the second track, and too much gain as it exceeds the 0db threshold in the third track, which will produce a harsh clipping noise.
We can monitor the gain amplitude in any recording device. The receiving signal gain is indicated separately for each channel. If we work with stereo left (L) and right (R) channels, it will be indicated like this:
Some devices only output sound when they are armed. To arm a device means that we have prepared it for recording, and we can monitor the left and right signal gain input. Most often, the device will indicate arming with a blinking red light and recording with a solid red light plus a running duration of the recording time.
Sample rate, bit rate, and format
Sample rate to digital audio is like a pixel to a digital image. The sample rates most often used are 44.1kHz, 48kHz or 96kHz. The difference is minimal for the ear, but some prefer to work at a higher resolution. However, when you record in one resolution, you should use the same resolution in production when creating your composition in a DAW. For video and film, the standard is 48kHz. Some recordists also decide to record at 96kHz, which might take more memory space and prove impractical in the long run.
Bit rate refers to the number of bits used per second to represent a continuous medium. The encoding bit rate of a multimedia file is its size in bytes divided by the playback time of the recording (in seconds), multiplied by eight, and it comes in the rate of 8-bits, 16-bits, 24-bits, 32-bits/float. We should opt for a bit rate as high as possible; the higher the bit rate, the bigger the file size. Some recording devices’ highest bit rate is 24 bits, while some more expensive devices have a 32-bit/float rate.
Container: An audio container is a format in which we package our recording. So the bit rate and sample rate determine the resolution of our digital recording, and the format determines how this resolution translates through codecs into audio for our devices to read. Always use hi-res and lossless formats: WAV is the most widely used as all the devices and platforms find it easy to playback; it is lossless quality but quite large. Alternatively, if you need to make your file smaller without risking the quality of the recording, use .FLAC (Free Lossless Audio Codec). A lossless Apple format is AIFF. Avoid using compressed formats such as MP3, OGG, or AAC.
How to choose your recorder
Choosing a suitable recorder to fit one’s needs and budget can be confusing for beginners. I do not recommend using small dictaphones and mobile phone recorders as they do not offer the possibility of recording high bit rate, lossless format and gain setting. Ideally, we would wish to record a .wav format, not a compressed .mp3 or, even worse .wma format; and have at least three stages of gain setting (low, mid, high). Low-cost recorders for beginners (100-200€) are Tascam DR-05X or Zoom H series (H2n, H4n). Fairly better mid-cost recorders (200-800€) are Tascam DR-40X or Zoom F series (F4, F6, F8). The latter do not have inbuilt mics as the manufacturers anticipate the user will opt for high-grade microphones. High-cost recorders for professional field recordists are the SoundDevices (800 to 1.200€) Mixpre II Series. They also do not have inbuilt microphones but offer a wide range of settings and exquisite preamps that produce almost no audio noise.
Recording directly with a computer
For those who don’t have an audio recorder, I strongly discourage plugging the EMF detector directly into their computer jack input. An optimal setup for recording in an audio editor (Audacity) or DAW (Reaper) is with an audio interface or so-called external sound card. To learn more about the role of an audio interface in your setup or home studio, please refer to What Is An Audio Interface? by Music Repo. To learn more about recording in Audacity or Reaper, please refer to the Audacity and Reaper Tutorial by Music Repo. To preserve a stereo picture in the recording with a direct connection through the audio interface to the computer, you will need a cable that splits your stereo 3.5mm jack of EMF detector to a double 6.3mm mono jack which you plug into the audio interface mono jack inputs.
Indexing
Immediately after a recording session, take some time to sort out your recordings when the memory of the trip is still fresh. Important! Always create a new map for the archive of your recording day and rename it in a way you will easily recall later, for example, 20220226-EMF-workshop. Different people have different associative flows. Some find it easy to remember dates, others remember events or locations, and some like thematic filing. Whichever you choose, ensure your indexing and filing system is consistent. Make sure that you successfully copied your recordings from SD to your drive. Go through your notes and delete unwanted and unsuccessful recordings. Always keep raw files. Never delete them when you have made audio editing, as you never know when you might wish to cut or manipulate them differently. Make a selection of recordings that you want to use in postproduction.
Next step: Mixing
To learn how to use the recordings in a composition, please refer to the third part of the workshop Mixing with EMF recordings or return to the workshop page: Electromagnetic Field Detector.
Teaching materials were commissioned by konS – Platform for Contemporary Investigative Art and produced by Rampa Lab and LokalPatriot.