I have a number of MP4 files which are also available on YouTube, since long ago.

These videos are basically showing Music Sheets while a Piano is playing them.
The piano is not real, so this is quite similar to playing a MIDI file.

I understand MIDI files can have different sounds and behaviors depending on the devices playing them, but I expect Videos/Audio files should always play the same.

One strange behavior I noticed today is that these videos are suddenly playing the "higher notes" of Piano a bit "out of tune", like if notes are being played wrong or piano needs to be tuned.

Two examples below. What I mean can be heard from beginning of the first video, and almost at the end of the second video (1:50 to 2:00).



What I tried:
- PC with speakers (that's how I noticed the issue)
- PC with headphones
- Mobile phone
- YouTube (in case my MP4 files were corrupt)
- Converted to MP3

ALL of these have the same weird high-note problem.

I'm absolutely sure I was hearing the songs/notes properly before.

How can this be explained, given that the files (and YouTube video) weren't changed, and the same behavior is happening on both PC (Windows) and Mobile (Android) ?

  • Those examples sound great to me (macOS Mojave 10.14 on a MacBook Pro, playing through Safari). Nothing off-key or out of tune. I'm not sure this relates, but the .mp4 container file format is based on QuickTime, and QuickTime had the ability to have MIDI tracks, and your playback system would have to support MIDI in order to turn the MIDI instructions in those tracks into actual instrument sounds. So I suppose there's a small chance that your files really have MIDI tracks rather than sampled audio tracks and that something's gone wrong with your playback systems' MIDI support. – Spiff Oct 29 '18 at 19:20
  • Upon further investigation, as best I can tell, these videos have prerendered audio as 44.1kHz AAC. I withdraw my MIDI track speculation. – Spiff Oct 29 '18 at 19:28
  • Thank you @Spiff. That does make sense and is very interesting anyway - good to know! The following video is an actual recording, and even that one, at around 4:23 ~ 4:26, many high notes are also "out of tune" to me. So, we may discard the "MIDI" theory :) youtube.com/watch?v=jJDVVD-Nekk – Nuno Oct 29 '18 at 19:34

I've noticed this as well (and wondered why for quite some time), until a discussion about all sorts of sound related topics with my boyfriend's dad who is a sound engineer.

Other than the quality of the speakers on a device, I theorise that these kinds of things can also happen due to an effect known as "binaural beats", which has an effect on how you experience the frequency/pitch of sound when more than one note plays or there's other sounds in the background.

Say for example you play the notes C4 (261.63HZ)and D4 (293.66HZ) simultaneously, with the binaural beat effect, you'll also hear two other frequencies:

~ The frequencies added (261.63 HZ + 293.66 HZ = 555.29 HZ), which is between C#5/Db5 and D5

~ And the subtraction (293.66 HZ - 261.63 HZ = 32.03 HZ,) which is somewhere between B0 and C1

If you're listening to music on speakers, and there's background noise such as machinery or the sounds of nature, it can affect how you hear the pitch of the music. It definitely does for me, which is why I generally stick to sound blocking earphones when I listen to music.

  • Thank you for explaining, and I definitely thought about that. However, I tried different places, and even another device, in another room, etc. Also, when I put the headphones, I expect that it is less biased than if I hear with the speakers. There is no different sound in my house at the moment than when I heard the songs months/years ago. – Nuno Oct 29 '18 at 12:40

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