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Can A Spectrogram Explain A UFO Sound?
A spectrogram can reveal pulses, bands and pitch changes that the ear may miss in a strange sky-noise recording.
On this page
- What horizontal bands and pulses can suggest
- Aircraft, rotor, wind and machinery patterns
- Why visual audio clues still need context
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Introduction
A spectrogram is one of the most useful tools for checking an unusual sky-noise recording because it can reveal patterns that are difficult to hear in real time. Instead of showing sound as a simple waveform, a spectrogram displays frequency on one axis, time on the other and signal strength through colour or brightness. This makes repeating pulses, tonal bands, pitch shifts and hidden harmonics visible at a glance. [Wikipedia]WikipediaOpen source on wikipedia.org.
For people investigating alleged UFO noises, a spectrogram rarely provides a definitive answer on its own. What it often does provide is a clue about whether a sound behaves like a helicopter, drone, jet aircraft, industrial machine, wind effect or something less easily classified. The value lies in pattern recognition rather than proof. A strange sound that seems featureless to the ear may show a highly structured signature once analysed.
Can A Spectrogram Explain A UFO Sound?
Many reports of mysterious aerial sounds describe low hums, metallic drones, pulsing vibrations or distant rumbling. Human hearing is surprisingly poor at separating overlapping sounds, especially at night or over long distances. Spectrograms help because they convert those overlapping frequencies into visible structures. [Wikipedia]WikipediaList of unexplained soundsList of unexplained soundsThe following is a list of sounds which are currently, or were previously, unidentified. All of the NOAA sou…
When examining a recording, investigators often look for three broad features:
- Stable horizontal bands.
- Repeating pulses or rhythmic bursts.
- Frequency shifts over time. [vibrationresearch.com]vibrationresearch.comVibration Research What is a Spectrogram?What is a Spectrogram? - Signal AnalysisA spectrogram displays signal strength over time at the various frequencies present in a waveform…
Each can point towards different kinds of sound source.
A completely random atmospheric noise tends to appear as diffuse energy spread across frequencies. Mechanical systems, by contrast, often produce organised patterns that stand out clearly on a spectrogram. Rotating machinery, aircraft engines and propellers frequently generate repeated tonal structures and harmonics that remain visible even when the recording itself sounds confusing. [ResearchGate]researchgate.netResearchGateFrequency Destructive Interference curves and the…Harmonics in spectrograms of light airplanes collected by a stationary m…
What Horizontal Bands And Pulses Can Suggest
One of the most common findings in supposed UFO-noise recordings is the appearance of horizontal frequency bands.
Horizontal bands indicate that a sound is maintaining energy at roughly the same pitch over time. A single band may represent a steady tone. Multiple evenly spaced bands often indicate harmonics, meaning a fundamental frequency and its multiples. Harmonic structures are strongly associated with mechanical and rotating systems. [ResearchGate]researchgate.netResearchGateFrequency Destructive Interference curves and the…Harmonics in spectrograms of light airplanes collected by a stationary m…
For example:
- A steady low-frequency band may indicate an engine, generator or distant turbine.
- Multiple stacked bands can indicate propeller or rotor activity.
- Narrow bright lines often suggest a tonal source rather than natural broadband noise.
- Parallel bands that rise or fall together may indicate Doppler shifts caused by a moving aircraft. [ResearchGate]researchgate.netResearchGateFrequency Destructive Interference curves and the…Harmonics in spectrograms of light airplanes collected by a stationary m…
Pulses appear differently. Instead of continuous lines, the spectrogram shows repeated bursts separated by gaps. These can reveal:
- Rotor blade passages. [mdpi.com]mdpi.comMDPIExperimental Analysis of Rotor Blade Noise in Edgewise…by NS Jamaluddin · 2023 · Cited by 25 — The acoustic spectra demonstrated a…
- Drone propeller cycles.
- Rhythmic machinery.
- Periodic aerodynamic effects.
Researchers studying aircraft and rotor acoustics frequently identify blade-passing frequencies and their harmonics through these repeating patterns. The resulting visual signature can remain obvious even when the sound seems like an indistinct drone to a listener on the ground. NASA Technical Reports Server [2Acoustique École Centrale Lyon]acoustique.ec-lyon.frthe flight direction in the case of half-blade passage…Read more…
Why Rotor And Propeller Sounds Often Look Mysterious
Some of the most dramatic “unidentified” sounds become less mysterious when viewed as rotor-generated noise.
Helicopters, drones and propeller aircraft generate tones linked to blade-passing frequency. This occurs when rotating blades repeatedly disturb the air and create periodic pressure fluctuations. On a spectrogram, the result commonly appears as evenly spaced horizontal bands or ladders of harmonics. [acoustique]acoustique.ec-lyon.frthe flight direction in the case of half-blade passage…Read more… École Centrale Lyon [AIAA]arc.aiaa.orgAIAA JournalSpectral characteristics of rotor blade/vortex interaction noiseby RM Martin · 1988 · Cited by 15 — The trends of the blade p…
Distance complicates interpretation. Atmospheric conditions can remove higher frequencies while preserving lower ones. A helicopter several kilometres away may therefore lose its familiar chopping character and instead resemble a strange humming resonance. The spectrogram may still reveal harmonic spacing associated with rotor activity even when the listener no longer recognises the sound. [AIAA Journal]arc.aiaa.orgAIAA JournalSpectral characteristics of rotor blade/vortex interaction noiseby RM Martin · 1988 · Cited by 15 — The trends of the blade p…
Modern drones add another layer of confusion. Multiple rotors produce interacting tones and harmonics that can create unusual beating effects and fluctuating intensity patterns. Acoustic studies of quadrotor aircraft show that rotor systems generate tonal components at blade-passing frequencies alongside broader turbulence-related noise. [acoustique]acoustique.ec-lyon.frthe flight direction in the case of half-blade passage…Read more… École Centrale Lyon [MDPI]mdpi.comMDPIExperimental Analysis of Rotor Blade Noise in Edgewise…by NS Jamaluddin · 2023 · Cited by 25 — The acoustic spectra demonstrated a…
This is one reason why some recordings initially described as “alien” or “otherworldly” later prove consistent with drone operations.
Aircraft, Rotor, Wind And Machinery Patterns
The strongest use of a spectrogram is comparison.
Aircraft Signatures
Aircraft often produce visible frequency shifts as they approach and recede. The Doppler effect can cause harmonic bands to curve upward and then downward through time. Research on aircraft acoustic signatures specifically uses spectrogram harmonics to estimate aircraft movement and characteristics. [ResearchGate]researchgate.netResearchGateFrequency Destructive Interference curves and the…Harmonics in spectrograms of light airplanes collected by a stationary m…
Jet aircraft can also generate multiple tonal components, especially during high-power operation. Fan and compressor systems create harmonic structures that may appear as parallel bands. [research.chalmers.se]research.chalmers.seAircraft Noise Prediction: from Trajectory to Synthesisby EM Thoma · 2024 · Cited by 5 — Tones are generated at integer multiples of the…
Rotor Systems
Rotor systems tend to produce repeating tonal ladders. Harmonics frequently appear at predictable intervals, corresponding to blade-passing events and rotational speed. Investigators often look for these evenly spaced patterns when checking recordings attributed to unknown aerial objects. NASA Technical Reports Server [2Acoustique École Centrale Lyon]acoustique.ec-lyon.frthe flight direction in the case of half-blade passage…Read more…
Wind Noise
Wind can produce surprisingly dramatic recordings while leaving a relatively different visual signature.
Strong wind striking a microphone often creates broadband energy spread across a wide range of frequencies rather than clean tonal bands. Gusts may appear as irregular clouds or bursts rather than stable harmonic structures. Recording studies consistently identify wind as a major source of contamination in environmental audio analysis. [ScienceDirect]sciencedirect.comScienceDirectInfluence of recording devices and environmental noise on…by C Zhang · 2024 · Cited by 26 — This study investigated the i…
This distinction matters because witnesses sometimes interpret microphone wind overload as an external atmospheric phenomenon.
Industrial And Infrastructure Sources
Factories, ventilation systems, pumps, turbines and electrical equipment often generate remarkably stable frequency bands. A distant industrial source can create a low-frequency hum that appears mysterious to nearby residents, particularly at night when background noise decreases.
Spectrogram analysis frequently shows that these sounds remain fixed in frequency for long periods, unlike aircraft or moving aerial sources. The stability itself becomes an important clue.
When A Spectrogram Reveals Something Unexpected
Not every recording fits a simple category.
Researchers in environmental sound classification regularly encounter mixed soundscapes where multiple sources overlap. A spectrogram can expose combinations that are difficult to hear directly, such as aircraft noise masked by wind, machinery mixed with traffic or overlapping drone and environmental sounds. [Nature]nature.comNatureEnvironmental sound classification using temporal…by W Mu · 2021 · Cited by 159 — A temporal-frequency attention based convoluti… [MDPI]mdpi.comEfficient Classification of Environmental Sounds through…by Z Mushtaq · 2020 · Cited by 76 — This paper reports our study on employing…
In some cases, a recording that initially seems dominated by one strange tone turns out to contain several independent sources operating simultaneously. A low-frequency industrial hum might sit beneath an aircraft pass, creating a composite sound that feels unusual to witnesses.
This possibility is important because many famous mystery-sound reports occur in acoustically complex environments rather than quiet laboratory conditions.
One example discussed within unidentified aerial phenomenon circles involved a reported mystery sound whose spectrogram showed nearby aircraft signatures complicating interpretation. The visual evidence did not automatically identify the source, but it demonstrated how easily aviation noise can overlap with supposedly anomalous recordings. [Medium]avi-loeb.medium.comMystery Sound of an Unidentified Anomalous PhenomenonMediumMystery Sound of an Unidentified Anomalous PhenomenonNovember 10, 2023 — Here is a spectrogram of 10 minutes with the mystery sound…
Why Visual Audio Clues Still Need Context
A spectrogram is powerful, but it is not a lie detector for UFO claims.
Several factors can create misleading patterns:
- Microphone distortion.
- Automatic gain control in phones.
- Wind striking the microphone.
- Compression artefacts from social media uploads.
- Echoes from buildings or terrain.
- Multiple overlapping sound sources. [ScienceDirect]sciencedirect.comScienceDirectInfluence of recording devices and environmental noise on…by C Zhang · 2024 · Cited by 26 — This study investigated the i…
The same visual structure can also arise from very different physical causes. A harmonic ladder might indicate a helicopter, a drone, a turbine or another rotating machine. Identification usually depends on combining the spectrogram with time, location, weather conditions and known activity in the area.
This is why professional acoustic monitoring projects place such importance on metadata and environmental context rather than relying on the image alone. A spectrogram can show that a sound is organised, periodic or mechanical, but it cannot automatically reveal what produced it. [White Rose eTheses Online]etheses.whiterose.ac.ukMCG ThesisWhite Rose eTheses OnlineEnvironmental Sound Monitoring Using Machine Listening…4 Feb 2021 — This thesis investigates how the technolo…
For UFO-noise investigations, the most useful approach is to treat the spectrogram as evidence of structure rather than evidence of origin. It can reveal hidden pulses, harmonics and frequency movements that the ear misses, helping separate genuinely unusual recordings from sounds that match known aircraft, rotorcraft, weather or machinery behaviour. [Vibration Research]vibrationresearch.comVibration Research What is a Spectrogram?What is a Spectrogram? - Signal AnalysisA spectrogram displays signal strength over time at the various frequencies present in a waveform…
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Further Reading
Books and field guides related to Can A Spectrogram Explain A UFO Sound?. Use these as the next step if you want deeper reading beyond the article.
The Sound Book: The Science of the Sonic Wonders of the World
Introduces how sound behaves and how unusual noises can be interpreted.
Practical Recording Techniques
Covers audio analysis concepts useful when interpreting spectrograms.
The Audio Expert
Explains frequencies, harmonics and signal behavior visible on spectrograms.
How to Read a Paper
Encourages evidence-based interpretation rather than overreading patterns.
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Endnotes
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Source: Wikipedia
Link: https://en.wikipedia.org/wiki/Spectrogram -
Source: nature.com
Link: https://www.nature.com/articles/s41598-021-01045-4Source snippet
NatureEnvironmental sound classification using temporal...by W Mu · 2021 · Cited by 159 — A temporal-frequency attention based convoluti...
-
Source: researchgate.net
Link: https://www.researchgate.net/figure/Frequency-Destructive-Interference-curves-and-the-Spectrogram-of-light-plane-LB-3C_fig5_261395223Source snippet
ResearchGateFrequency Destructive Interference curves and the...Harmonics in spectrograms of light airplanes collected by a stationary m...
-
Source: research.chalmers.se
Link: https://research.chalmers.se/publication/540965/file/540965_Fulltext.pdfSource snippet
Aircraft Noise Prediction: from Trajectory to Synthesisby EM Thoma · 2024 · Cited by 5 — Tones are generated at integer multiples of the...
-
Source: ntrs.nasa.gov
Link: https://ntrs.nasa.gov/api/citations/19770026169/downloads/19770026169.pdfSource snippet
NASA Technical Reports Serverstudy of noise and inflow distortion sources in the nasa qf-...October 3, 2000 — by DB Hanson · 1977 · Cite...
Published: October 3, 2000
-
Source: mdpi.com
Link: https://www.mdpi.com/2226-4310/10/6/502Source snippet
MDPIExperimental Analysis of Rotor Blade Noise in Edgewise...by NS Jamaluddin · 2023 · Cited by 25 — The acoustic spectra demonstrated a...
-
Source: arc.aiaa.org
Link: https://arc.aiaa.org/doi/pdf/10.2514/3.45542Source snippet
AIAA JournalSpectral characteristics of rotor blade/vortex interaction noiseby RM Martin · 1988 · Cited by 15 — The trends of the blade p...
-
Source: sciencedirect.com
Link: https://www.sciencedirect.com/science/article/pii/S1470160X24002164Source snippet
ScienceDirectInfluence of recording devices and environmental noise on...by C Zhang · 2024 · Cited by 26 — This study investigated the i...
-
Source: mdpi.com
Link: https://www.mdpi.com/2073-8994/12/11/1822Source snippet
Efficient Classification of Environmental Sounds through...by Z Mushtaq · 2020 · Cited by 76 — This paper reports our study on employing...
-
Source: avi-loeb.medium.com
Title: Mystery Sound of an Unidentified Anomalous Phenomenon
Link: https://avi-loeb.medium.com/mystery-sound-of-an-unidentified-anomalous-phenomenon-09d1cb461cd2Source snippet
MediumMystery Sound of an Unidentified Anomalous PhenomenonNovember 10, 2023 — Here is a spectrogram of 10 minutes with the mystery sound...
Published: November 10, 2023
-
Source: sciencedirect.com
Link: https://www.sciencedirect.com/science/article/pii/S1000936119301098Source snippet
As shown in Fig...
-
Source: researchgate.net
Link: https://www.researchgate.net/publication/345260947_Efficient_Classification_of_Environmental_Sounds_through_Multiple_Features_Aggregation_and_Data_Enhancement_Techniques_for_Spectrogram_ImagesSource snippet
(PDF) Efficient Classification of Environmental Sounds...3 Nov 2020 — This paper reports our study on employing various acoustic feature...
-
Source: Wikipedia
Title: List of unexplained sounds
Link: https://en.wikipedia.org/wiki/List_of_unexplained_soundsSource snippet
List of unexplained soundsThe following is a list of sounds which are currently, or were previously, unidentified. All of the NOAA sou...
-
Source: news.sky.com
Title: mysterious sounds could help scientists detect deadly tornadoes 11870750
Link: https://news.sky.com/story/mysterious-sounds-could-help-scientists-detect-deadly-tornadoes-11870750Source snippet
sounds could help scientists detect deadly...26 Nov 2019 — The research team suggests with more tests, they could be able to detect a to...
-
Source: vibrationresearch.com
Title: Vibration Research What is a Spectrogram?
Link: https://vibrationresearch.com/blog/what-is-a-spectrogram/Source snippet
What is a Spectrogram? - Signal AnalysisA spectrogram displays signal strength over time at the various frequencies present in a waveform...
-
Source: acoustique.ec-lyon.fr
Link: https://acoustique.ec-lyon.fr/publi/roger_acoustics20.pdfSource snippet
the flight [direction]({{ 'direction/' | relative_url }}) in the case of half-blade passage...Read more...
-
Source: etheses.whiterose.ac.uk
Title: MCG Thesis
Link: https://etheses.whiterose.ac.uk/id/eprint/28401/2/MCG_Thesis.pdfSource snippet
White Rose eTheses OnlineEnvironmental Sound Monitoring Using Machine Listening...4 Feb 2021 — This thesis investigates how the technolo...
-
Source: kaggle.com
Link: https://www.kaggle.com/code/salimhammadi07/esc-50-environmental-sound-classificationSource snippet
ESC-50: Environmental Sound ClassificationA spectrogram can be useful for visualizing the frequency content of a sound over time, and for...
Additional References
-
Source: headcountcoffee.com
Title: unexplained sound phenomena and acoustic anomalies
Link: https://www.headcountcoffee.com/blogs/coffee-news/unexplained-sound-phenomena-and-acoustic-anomalies?srsltid=AfmBOoqXZ5SiYM_H6Xuv9etL87wDcuSJKjPt10kHMC3JrUb0h1APJs-RSource snippet
1 Apr 2026 — Strange sounds from [sky trumpets]({{ 'sky-trumpets/' | relative_url }}) to the [Taos Hum]({{ 'taos-hum/' | relative_url }}). Explore unexplained acoustic phenomena, fear triggers, and...
-
Source: soundoflife.com
Title: strange sounds heard around the world
Link: https://www.soundoflife.com/blogs/experiences/strange-sounds-heard-around-the-worldSource snippet
The Most Mysterious Noises Heard Around the World2 Apr 2023 — Coming from our planet's surface, the ocean depths and even outer space, he...
-
Source: repository.cam.ac.uk
Link: https://www.repository.cam.ac.uk/items/6aba81ef-0d56-4cac-9e4e-ea3cc19f0260Source snippet
Cambridge University RepositoryRetrieving spectral information of individual noise sources...by I Besnea · 2026 — For the A321neo and th...
-
Source: bruit.fr
Link: https://www.bruit.fr/revues/78_09968.PDFSource snippet
Active control of the blade passage frequency noise level of...by J Schulz · Cited by 25 — In this study, the required anti-phase sound...
-
Source: pmc.ncbi.nlm.nih.gov
Link: https://pmc.ncbi.nlm.nih.gov/articles/PMC12064345/Source snippet
OF NOISE GENERATED BY WIND TURBINES...by A Staniek · 2025 · Cited by 1 — This paper presents an analysis of selected low-frequency noise...
-
Source: arxiv.org
Link: https://arxiv.org/abs/2603.08154 -
Source: worldscientific.com
Link: https://www.worldscientific.com/doi/10.1142/S2251171723400056?srsltid=AfmBOoprMOp_29picHTMUIzUMKYjHX3TOxnryyIkUbnrSvxwti8O8Vv6Source snippet
Multi-Band Acoustic Monitoring of Aerial Signaturesby A Mead · 2023 · Cited by 10 — A passive, multi-band, field microphone suite designe...
-
Source: arxiv.org
Title: arXiv Low-Frequency Intensity Modulation of High-Frequency Rotor Noise
Link: https://arxiv.org/abs/2310.01056 -
Source: youtu.be
Title: How to interpret a Spectrograph
Link: https://youtu.be/xZfHCvMrTh8Source snippet
Spectrogram Deep Dive: Visualize and Hear the Hidden World of Data - YouTube BioniChaos...
-
Source: frontiersin.org
Link: https://www.frontiersin.org/journals/ecology-and-evolution/articles/10.3389/fevo.2021.761147/fullSource snippet
Using a Novel Visualization Tool for Rapid Survey of Long-...by S Brodie · 2022 · Cited by 14 — This paper explores the efficacy of usin...
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