Mains Hum Audio Analysis

What is this?

From https://en.wikipedia.org/wiki/Mains_hum:

Mains hum, electric hum, cycle hum, or power line hum is a sound associated with alternating current which is twice the frequency of the mains electricity. The fundamental frequency of this sound is usually double that of the local power-line frequency: that is to say, 100 Hz in areas with 50 Hz power, and 120 Hz in areas with 60 Hz power. The sound often has heavy harmonic content above 50/60 Hz. Due to the presence of mains current in mains-powered audio equipment as well as ubiquitous AC electromagnetic fields from nearby appliances and wiring, 50/60 Hz electrical noise can get into audio systems, and is heard as mains hum from their speakers.

The hidden background noise that can catch criminals 5 min. youtube video

Mains Hum (https://www.open.edu/openlearn/history-the-arts/recording-music-and-sound/content-section-6.2)

Anything electrical that is plugged into the mains can be susceptible to hum. Mains electricity is an alternating current, whereas something like a battery provides direct current. In the UK the mains voltage is about 240 V, with a frequency of 50 Hz. Most of Europe has a voltage of 220 V at 50 Hz, while the USA has a voltage of 110 V and a frequency of 60 Hz.
The voltage doesn’t cause noise, but the fact that it is alternating and not direct current can cause problems. The 50 Hz frequency (in the UK and Europe) can interact with some components inside electrical devices such as transformers, and can cause a vibration which is audible as a hum. The fundamental frequency of this hum is usually 50 Hz, (or 60 Hz in the USA), but just like a musical instrument, this can have a number of additional harmonics.

ENF Power Signature (https://www.mast.umd.edu/research.php?t=enf)

The Electric Network Frequency (ENF) is the frequency of power distribution networks in power grids; it is nominally 60Hz in North America and 50Hz in most other places. The ENF does not stay at this nominal value, but fluctuates around it due to changing loads in the power grid. What makes the ENF useful for forensic purposes is that it can be captured by audio or video recordings due to electromagnetic influences.

The hum that helps to fight crime (https://www.bbc.com/news/science-environment-20629671)

"The power is sent out over the national grid to factories, shops and of course our homes. Normally this frequency, known as the mains frequency, is about 50Hz," explains Dr Alan Cooper, a senior digital forensic practitioner at the Met Police.
Any digital recording made anywhere near an electrical power source, be it plug socket, light or pylon, will pick up this noise and it will be embedded throughout the audio.

Exploring Power Signals for Location Forensics of Media Recordings (https://sigport.org/sites/default/files/docs/10Hertz_Paper.pdf)

Electric network frequency is a newly developed emerging technology of today. This inherent feature of audio and video recordings is a foolproof method for forensic analysts to determine their authenticity and to retrieve the time and location of the original signal recording.
Although the variations maybe random there can be found a regularity to its fluctuations about the nominal value, which is 60Hz in North America and 50Hz in most other places.
The recorded ENF might contain harmonics as well, which might have a power higher than the fundamental frequency. So harmonics are to be considered in analysis of ENF; even though harmonics above 3rd harmonic might not be useful due to their contamination by lower frequency audio signals
The ENF components of electric grids are centered either at 50Hz or 60Hz and their first harmonics fall around 100Hz and 120Hz.

Mains Electricity By Country (https://en.wikipedia.org/wiki/Mains_electricity_by_country)

How can this be used?

We can use the above knowledge to turn an audio file into a visual representation and look for any hums.
A spectrogram visually represents audio signals in terms of frequency (y-axis) and time (x-axis). A consistent peak at either 50 Hz or 60 Hz on the spectrogram indicates a hum. We may also see harmonics (multiples) of these frequencies (e.g., 100 Hz, 150 Hz for 50 Hz hum or 120 Hz, 180 Hz for 60 Hz hum). These are useful for confirming the presence of the fundamental frequency. A hum typically manifests as a continuous peak rather than a transient sound.

Hiding the Hum, or Why we can't always see it

• A professional setup significantly reduces or mask hum to get clean voice audio free from external noises.
• Band-pass and Low-pass filters are used to cutoff frequencies below a certain threshold that are normally inaudible to the human ear.
• A noise gate selectively allows only audio signals above a specified volume threshold to pass through. Thus, whenever the streamer is not speaking, the noise gate prevents any audio (including potential hum) from being transmitted, leading to minimal detectable noise.
• A compressor reduces gain when music or game audio are playing to prevent clipping, lowering the volume of everything and reducing the relative visibility of an already quiet hum.
• Vtubers and professional streamers utilize audio interfaces or mixers that feature built-in real-time filters to get cleaner audio.
  Because of these techniques it is rare to find visible traces of mains hum in professional audio recordings.

Gawr Gura Audio Analysis

To download the audio of a youtube video we use yt-dlp (this will generally be around 60mb/hour): yt-dlp https://youtu.be/example -f bestaudio -o downloaded_audio
We then use ffmpeg to convert the downloaded audio into an uncompressed WAV (resulting file will be around 600mb/hour): ffmpeg -i downloaded_audio -c:a pcm_s16le uncompressed_audio.wav
Finally we open the WAV into a software to display its spectrogram. I used iZotope RX as it has useful function to focus on specific amplitude and frequency ranges, but even something Audacity should work.
No amplification/compression/filtering/audio or image altering of any kind was done for anything on this page.

You are encouraged to do your own tests and not take my word for anything on this page. I have done this to the best of my ability, without cherrypicking or ignoring anything that goes against my assumptions.

I downloaded and looked at the spectrograms of a number of videos, particularly watchalongs as they have no BGM/game sounds, and VR as they use a different mic setup that presumably isn't subjected to the same filtering as the main mic.

If files 404 download the archive: https://anonfile.co/zw9zqb2F7eha5nX/file

NOTE: All images are scaled down on this page. Right click images and open in a new tab for the full size.

Oct 16 2020 - Ghostbusters

Members-only movie watchalong.

Easy to see 60/120hz hum in a watchalong with no BGM or game audio.

Feb 5 2021 - Blue Planet

This is a member-only documentary watchalong with no BGM after the first 10 minutes.

Pretty much the same as above, except 120hz is less visible.

Apr 19 2021 - Super Metroid

https://youtu.be/htSesevc0fw?t=10255
Full Spectrogram
Nothing obvious. At certain timestamps such as 02:51:00, when the game is quiet, she starts speaking and a 120hz signal get picked up, perfectly synced with her voice (noise gate).

Audio/Video Spectrogram Clip

Jun 16 2021 - Sharknado

This is a member-only movie watchalong with no BGM or other noises except during the intro and outro.

Haven't looked at this closely but 60/120hz signals are very clear.

Jun 20 2021 - Jaws

A public movie watchalong for her birthday. Same observation as above with the 60/120hz signals.

Sep 16 - Oct 12 2021 - Asobi Asobase

3 streams of a members-only anime watchalong.
Sep 16 Spectrogram - Sep 27 Spectrogram
Nothing obvious in the first 2 recordings.
Oct 12:

In the third stream we start seeing a 50/100hz hum whenever she's speaking, instead of the 60/120 before.

Oct 14 2021 - Minecraft

https://youtu.be/s0Tae_MdgPQ
Spectrogram
Nothing immediately obvious with BGM and game sounds.
Zooming in can show 50/100/200hz signals synced with her mic:

Audio/Video Spectrogram Clip

Nov 12 2021 - VR Skyrim

https://youtu.be/Jm5prJAYamA?t=3855
Full Spectrogram
Faint but visible 50/100hz hums throughout the recording.
The 50/60hz signal is clear during a quiet moment after 1:04:30:

Jan 20 2022 - Apotheon

https://youtu.be/1Gv5O0Q1DDc?t=470
Full Spectrogram
After 7:55 the 100hz/200hz signals match perfectly with her speech:

After 10:05 for a short moment only her voice can be heard, and the 100hz/200hz signals are visible:
Spectrogram{85%:85%} Audio/Video Spectrogram Clip

Jan 22 2022 - Superhot

https://youtu.be/8D1HlqdAeJg?t=2748
Full Spectrogram
After 45:50 there is little sound coming off the game, and there are 50hz/100hz signal spots matching her speech:

The same happens after 1:37:20:
Zoom
Audio/Video Spectrogram Clip

Feb 9 2022 - Nintendo Direct

Members-only watchalong.

Constant 50/100/200hz signals throughout.
Zoom

Feb 16 2022 - VR Minecraft

https://youtu.be/xgBXRUsqjsc?t=2175
Full Spectrogram
Nothing jumps to the eye. At certain points such as 36:30 and 49:20, the 50/100/200hz signals show up. I don't know why they are isolated and not constant throughout the recording.

The sudden jump in loudness may be a consequence of compression. If dynamic range compression is applied, it can cause quieter sounds (like the hum) to be more prominent when louder sounds are reduced. After speech, the background hum may be more audible.

Apr 23 2022 - Saturday Morning Cartoons

A members-only cartoons watchalong.

Zoom
Visible hums at 50/150/250hz, faint but still visible hums at 100hz and 200hz.

Jul 5 2022 - Tadaima

https://youtu.be/k_skfzMMyso
Chatting stream after returning from Japan. Constant BGM throughout.
There's constant a 180hz hum throughout the clip synced to her voice (noise gate). It becomes more apparent after she says she lowered her mic threshold after 7:20.
Audio/Video Spectrogram Clip (look at 180hz)

Aug 31 2022 - hewwo

Another members-only chatting stream with BGM.

Hard to see anything definitive, but there's traces of the same 50/100/200hz hum as the Nintendo Direct and VR Minecraft streams, with stronger signals between minutes 0:05-0:13, 0:43-0:58, and 1:40-1:46.

Oct 20 2022 - Resident Evil Showcase Reaction

https://youtu.be/pKa8iAs0gb0?t=3792
Full Spectrogram
A watchalong of another stream so most of it has unrelated noises. After 1:03:20 the showcase ends and we can hear a 50/100/150hz signal.

Apr 5 2023 - Fresh Catch

Members-only chatting stream with a light BGM. Can't spot a 50/60hz line but the following analyzed recordings appear similar to me.
Spectrogram

Apr 22 2023 - Scooby Doo Watchalong

Members-only movie watchalong.

Strong 60/120hz signals.

Aug 15 2023 - Outer Wilds

https://youtu.be/YDE376Lqjn8?t=18586
Very long stream filled with game noises.
At 5:07:00 we can see a 60/120/180hz signal, though it's not synced to her speech, it could be part of the game: Zoom 1
After 5:09:50 she quits the game and speaks without BGM for a short while: Zoom 2

Feb 9 2024 - Members News

Members-only chatting stream.

Very strong 50/100/200hz signals and a faint 150hz.

Feb 14 2024 - ASMR

Members-only ASMR Valentine special.

Looks unlike the other February recordings and similar to the Scooby Doo watchalong with the 60/120hz hum, possibly pre-recorded long in advance.

Feb 23 2024 - Think Fast Chucklentus

Members-only chatting stream. Louder than usual BGM.
Full Spectrogram
Hard to see but 50/100/200hz hum shows throughout.
Zoom 1

Jul 14 2024 - TAKE 2

Members-only chatting stream. First third has louder BGM.
Full Spectrogram
Lots of noise but a faint 50/100hz hum can be seen.
Between 1:57:00 - 2:09:00 when the BGM is quieter the signal gets noticeably more noticeable at 50/100/200hz:

These signals are once again matching her microphone activity.
Audio/Video Spectrogram Clip

Apr 5 2025 - Logging In

Members-only chatting stream with BGM.
Full Spectrogram
After 48:30 we can see a 100hz line synced to her speech:

Audio/Video Spectrogram Clip

Apr 16 2025 - important announcement

https://www.youtube.com/watch?v=7WFg2wq10rw

Talking stream with no BGM. 50hz line is present throughout the recording.
Zoom

Apr 20 2025 - chat + announcing my final project

https://youtu.be/3pS6f3_veik
Full Spectrogram
Chatting stream with BGM.
100/200hz hum shows between minutes 13-19 and 42-45:

Audio/Video Spectrogram Clip

Sameko Saba Audio Analysis

Jul 1 2025 - 1 Million Subscribers

https://youtu.be/7Dj2_NQB7Jw
Full Spectrogram
Chatting stream with constant BGM.
Can't find anything interesting. Faint constant line at 90hz that could be the same seen in the Outer Wilds stream.

Jul 3 2025 - Resident Evil 4

https://youtu.be/VwYAZbXSxmY
Again nothing is immediately obvious. The first 25 minutes are the main menu music.
Full Spectrogram
After 3:10:10 we have spots of a 50/100hz signal synced with her speech (noise gate):
Zoom
Audio/Video Spectrogram Clip

Oct 30 2025 - Halloween Scary VR Games

Halloween VR stream. Has BGM and game sounds. She is using a different headset than in any previous Saba stream.

The 50hz, 90hz, 160hz look comparable to the TAKE 2 stream.
At 14:40 the BGM is looping and for a couple seconds we only get her clear voice. After 15:50 she shuts off the BGM and is about to start the game yet.

At both timestamps her mic is open and the 50hz hum comes through. Closer Zoom
Audio/Video Spectrogram Clip

Other Vtubers

To validate the above recordings, I've analyzed other vtubers with publicly confirmed locations, where the detected ENF frequencies matched their regional power standards, strengthening confidence in the results.

Dec 5 2020 - Amelia (NA)

https://www.youtube.com/watch?v=cOgynhXPKKw

ASMR stream. 60/120hz clear as day.

Apr 7 2022 - Kronii (NA)

https://youtu.be/J4ML65juR8o

Movie watchalong. 60/120hz can be seen in the left part of the image. BGM starts after 1:28:15. Still, after zooming in, 60hz and 120hz constant hums become clear again.
Zoom

Jun 25 2022 - Kiara (NA)

https://www.youtube.com/watch?v=gkOPn0P21F8

Kiara is in the USA for this chatting stream. She has BGM on. 60/120hz hums are immediately visible on the spectrum.

Oct 31 2022 - Fauna (NA)

https://youtu.be/oT5WJfMM9cc

Watchalong. Weak 60hz and clear 120hz.

Sep 2 2023 - Ame (NA)

https://www.youtube.com/watch?v=1xdWcr--hZo

Movie watchalong. Only a 120hz hum is constant throughout.

Oct 9 2023 - Kiara (EU)

https://youtu.be/KUouL2LPRDE?t=4280

Kiara is in the EU (1:11:20). 50/100/150/200hz bands can be observed across the recording particularly on the right side of the image.

Nov 1 2025 - CC (EU)

https://youtu.be/oyYgeVvHO2Y

Movie watchalong. Not the cleanest spectrum but we can make out constant signals along the 50/100/150/200hz frequencies particularly on the right side of the image.

Ping

Ping is used to measure latency, that is the round-trip time (RTT) for how long it takes one packet to go from your computer to another and back. Latency depends on various factors, including routing path and how many hops they go.

Latency can be made worse by network conditions, but never better than what distance allows.
High ping is NOT proof of high distance, as it's possible to take a bad route, be using a VPN, having a bad connection generally, etc.
Low ping, however, IS proof of low distance, or at least rules out long distance.
It is possible for someone in Los Angeles connecting to a server in San Francisco to have a 200ms ping.
It is NOT possible for someone in Berlin to connect to a server in San Francisco and have a 80ms ping.
So while having a high ping is not proof the other end is far away, having low ping is effectively proof of short distance.

Oct 24 2021

Gura hiding ping with overlay: https://youtu.be/al8l8J2qDRA?t=229

Kiara ping: https://youtu.be/qazuzvxL0e4?t=214
Irys ping: https://youtu.be/OMy4QY1VbiI?t=276
Kronii ping: https://youtu.be/y1z9ib6QBgI?t=208
Fauna ping: https://youtu.be/HuXDcwUflJU?t=476
Images: Kiara Irys Kronii Fauna
(others not shown here also used the overlay to hide their pings this stream)

She did not have a problem showing ping before. https://youtu.be/372fjz1T80I?t=896 https://youtu.be/ydkLps8LXzo?t=287

Feb 4 2022

250 ping to Mori in Japan: https://youtu.be/EHGTyH6aUr0?t=345

Proof Mori was in Japan: https://youtu.be/0WshLMuaCBI?t=9407
Expected ping times to Japan are: WC USA 80-130, EC USA 100-160, Central Europe 150-220

Apr 19 2022

https://youtu.be/00B097-mwOA?t=1082
Overwatch 2 stream. Ping is not shown on screen.
They are playing on a Japanese server and her game is noticeably laggy. At 18:02 Gura hits an enemy with the hammer and about 300ms pass between the hit spark on the enemy and her game receives feedback and her ultimate is charged.
After 2:04:00 they change game regions to America and it does not get much better for her. At 2:43:10 she attacks again and there is a similar delay between her hit spark and the ultimate getting charged.

Apr 13 2025

https://youtu.be/qgYK9k2KF7Q?t=10216
REPO collab with Kronii (host, NA), Raora (Japan), Kiara (EU)

NA server fits with everyone's pings. Gura's 120ms ping is not low enough to rule out she's in Europe.
Note during this and other REPO streams the ping glitches between showing the same number for everyone.
Raora in Japan: https://youtu.be/CV7ivk3Lf30?t=2015
Kiara in EU: https://youtu.be/9XCphnpE2U0?t=10509

Oct 30 2025

https://youtu.be/nSXFLVV2914?t=599
During the REPO collab with Dooby and Lime, saba's ping was higher than Lime. Dooby is WC based and Lime is UK-based.

Lime is hosting the game, as the 'kick' and 'start game' options only show from her pov: https://youtu.be/ihJEHRM3B2c?t=1852
Supposedly, Lime couldn't directly host the game and they were assigned given a relay server. Based on Dooby's 80ms ping the server is most likely in North America.
Lime talking about VPN this stream: https://youtu.be/ihJEHRM3B2c?t=11521 - her VPN is only for the browsers, not for gaming: https://youtu.be/HDCCx8GRzM8?t=5560
Lime's ping to Marvel Rivals servers around the world: https://youtu.be/gZJQfBuR1rY?t=285

Conclusion

Spectrogram analysis across numerous recordings consistently revealed low-frequency signals matching the mains hum patterns of different power regions. Early streams displayed strong 60 Hz and 120 Hz components typical of 60 Hz power systems, while later ones showed 50 Hz and 100 Hz signals characteristic of 50 Hz regions. These shifts align closely with control samples from other vtubers whose regional locations are confirmed, indicating the observed transitions are unlikely to be random or purely equipment-related.
Complementary evidence from network latency further supports this interpretation. No instances of unusually low ping values were found that would contradict the idea of a regional move, such as latency consistent with a short-distance connection to North American servers during the 50 Hz phase. Instead, the available data aligns with what would be expected if the streamer were operating from a region using 50 Hz mains electricity.

In many recordings, the hum is only visible for short periods, during quiet moments when no background music, game audio, or ambient noise is present. This is expected, as professional streaming setups employ filters, compressors, and noise gates that suppress low-level background sounds whenever louder elements such as BGM or game audio are active. Consequently, these brief intervals of clear signal represent the best observable evidence available under typical streaming conditions.

While YouTube compression and audio processing limit the precision of ENF-based analysis, the consistent pattern of frequency changes, combined with the absence of low-latency data suggesting continued proximity to previous servers, provides a coherent and credible indication that her recording environment shifted between power regions.

but she could have changed/upgraded her equipment!

Doesn't explain the return to 60hz for the Apr-Aug 2023 streams, or the Valentine's 2024 ASMR which was likely recorded in 2023.

but she always had high ping!

Her ping was not high in the early streams, like Among Us linked above, it only started being "always high" after a certain point.