This is a beginner level introduction to EMF field recording. If you have not followed the Soldering EMF Tentacles Workshop 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 his shop LOM Audio whenever they are restocked.
The device detects electromagnetic waves as the voltage deference in coils changes. The voltage varies with the distance between the transmitter and receiver coil and the frequency of the transmitter signal. Conductive materials give a significant voltage difference ranging between 0 and 0.072 volts. The integrated circuit (IC) in our device 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 a real sensor. For that, you would have to have at least an amateur measuring device that detects: low-frequency electromagnetic field strength, electric field measurement, and radio-frequency field strength monitoring. In scientific laboratories, they 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 simplest 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 current, or Earth current, is an extremely low-frequency current that moves underground and results from both natural causes and human activity. The strongest are geomagnetical currents induced by changes in the outer part of the Earth’s magnetic field, and they are usually caused by interactions between the solar wind and the magnetosphere or solar radiation effects on the ionosphere.
Electromagnetic radiation in our environment causes some concern in regards to its effect on biotic organisms. Current studies show that their impact is closely related to the duration, frequency, and intensity of exposure. Strict regulation of exposure and citizens understanding of risks is therefore of utmost importance.
Low-frequency EM (lower than 100 kHz) are induced by alternating current and voltage used in the production, transmission, and consumption of electricity. 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 particularly 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, the level of exposure to these fields is relatively high, but still within the recommended values. It is not recommended to be exposed to high-voltage power lines for a longer duration. Low-voltage power lines cause much less exposure, and underground power lines 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 mouses, keyboards, cameras, babysitters, toys, 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 recommendable to know the sources of HF EM radiation in our environment and behave with caution, for example, never cover the receiver of our mobile device as radiation increases with decreased reception. As you will clearly observe with your EMF detector, the field strength of EM decreases rapidly with distance. Most people are exposed to only a small 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. 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 parts of the body 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
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; Near Infra-Red (NIR) 30 THz – 300 THz
Near Ultra Violet, visible (NUV) 300 THz – 3 PHz
Ionising Electromagnetic Frequency Range
Ionising radiation is caused by subatomic electromagnetic particles that have sufficient energy to change the atoms by detaching electrons from them. Ionizing radiation is used in a wide variety of fields such as medicine, nuclear power, research, and industrial manufacturing, but presents a potential health hazard if proper measures against exposure are not taken. Exposure to ionizing radiation causes cell damage, which is relative to time and frequency of exposure, the intensity of exposure and shielding from the exposure. The most prevalent damage to living tissue is ultraviolet radiation. The boundary between ionizing and non-ionizing radiation in the ultraviolet area is not sharply defined because different atoms ionize at different energies. The subatomic particles unlike other electromagnetic waves travel at a speed that is 1% greater than that of light. Ionizing 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.
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
Audio Frequency Range
Audio and EM frequencies are measured in Hertz, however, they are very different physical phenomena. Sounds needs particles of air to travel through space. Essentially sound is a vibration of molecules. When speaking about audio, we consider frequencies as perceived by the human ear. Animals and plants however have a much different reception spectrum and we will not address those here. Humans start to tactilely perceive sound from sub-sonic, that is, infrasonic range of about 10 Hz. We begin to hear sound with ears, not just by vibration, at about 20 Hz. Physical vibrating properties are somewhat significant in the entire low-frequency audio spectrum that ranges from 20 – 200 Hz. When listening to EMF we get such low frequencies with some induction hobs. Low frequencies sound softer 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 200 – 2.400 Hz. Human speech and most of our main acoustic instruments are in this range. We find it abundant in field recording with EMF detectors; anything like computer monitors, plugs, lights or phones… High frequencies range from 2.400 – 20.000 Hz. In music, we mostly 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, entirely silent with gradual old age hearing loss. We find high range frequencies in public transportation, wi-fi routers, 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 like that of turning a device on and off or a machine acceleration,
- textures and different qualities of noises (white, pink, brown, gray) 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.
- beepblip, Morphoiki, upcoming album, January 2022
Methods of Field Recordings with EMF
Walking: The most important method is observation. Using EMF detector, you will walk into a special virtual acoustic space that makes you hear the inaudible world around us. Essentially, what we are doing, is having our own electromagnetic walk around the city. A nice 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 body of work, each city has a particular electromagnetic smog footprint. A very interesting site is also anywhere 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 picture immediately in the field. Try and play with turning the device slowly or quickly around its own axis. In this way, you will record a moving spatial sound, and will not need automation in postproduction.
Make notes: It is important to remember the tracks that sounded particularly interesting to you. You may take down notes or just remember the consecutive number of a significant recording. This 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 that you found and the purpose for which you will use it. We aim at recording 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 sequence was just 2 minutes. After we estimate that the sequence has ended, we stop and thus store the recording.
Safety: Do not forget to press the Record button. This 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 mic and line. This is not optimal as microphones should produce a signal that is 10 times stronger than that of the line input. Our detector has two inductors connected each with its own OpAmp that is integrated into 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. To listen to our EMF detector, we use headphones plugged into a headphone output. Be careful not to set it too loud as you might damage your hearing.
Gain and Volume
Understanding gain and in particular 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) is receiving a line input. In acoustics, a maximal gain is at 0db (decibels). Any input signal that exceeds the 0db threshold is registered as sound distortion also known as clipping. If we wish to produce a distorted sound, we should always do that in postproduction in our DAW with a distortion VST. We should never do it with line input as this is not so great for our device and especially our hearing. An optimal average gain range is between -24db and -18db, an optimal maximal gain is -12db. The reason for this convention is that we wish to create a balanced recording that will produce a similar output when we play it back on any of the devices such as studio speakers, car radios, mobile devices, pads, computers, concert halls. Most simple recorders have three levels of gain: low, mid, high, and the setting is done with a knob on the device. Better recorders have a gain range from 0 to 100, in which case we should begin our recording monitoring at about 35 or lower. The gain in such devices is usually set in the menu in recording settings. The best recorders have the option of setting gain in decibels, in which case we should begin our recording monitoring at about -18db. These values should not be exceeded a lot as we risk distortion and recorder noise (at 50Hz).
The picture with three tracks of the same recording shows: gain that is too low in the first track and will produce a hiss in our recording if we wish to normalise it; 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, this 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 blinking red light, and recording with solid red light plus a running duration of the recording time.
Sample Rate, Bit Rate, 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 it is advisable that you 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 may prove to be unpractical 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. If bit rate and sample rate determine the resolution of our digital recording, then the format determines how this resolution is translated through codecs into audio for our devices to read. Try to 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 it is quite big. Alternatively, if you need to make your file smaller without risking the quality of the recording, use .FLAC (Free Lossless Audio Codec), however, it is not supported by Apple. A lossless Apple format is AIFF. Try to avoid using compressed formats such as MP3, OGG, AAC.
How to Choose Your Recorder
For beginners, choosing the right recorder to fit one’s needs and budget can be confusing. Small dictaphones and mobile phone recorders are not recommended as they do not offer a 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).
Decent 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 do not advise 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 know more about what is 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 Audacity and Reaper Tutorial by Music Repo. If you wish 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.
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 that 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, make sure your indexing and filing system is consistent for you. Make sure that your recordings are successfully copied 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 wish 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.
Teaching materials were commissioned by konS – Platform for Contemporary Investigative Art and produced by Rampa Lab and LokalPatriot.