[naltroc]

When I use an FFT to view the spectrogram on YouTube music videos, it is very obvious that YouTube applies a lowpass filter at 16kHz on all videos (true since 2023 at least).

While this does retain the majority of useful information, it explains why the youtube version of your song feels just a little more 'lifeless' than the high quality version you have elsewhere.

The original recording contains high frequency detail that got lost. Your human body uses that high frequency detail to orient itself in space with respect to sound sources (like reverb, reflections, or ambient sounds).

It is interesting from a data storage point of view because this could result in massive savings. Consider audio is recorded at 44.1khz or 48kHz but is actually stored at 32kHz. They have effectively saved 25% in audio file storage at marginal customer experience.

[nayuki]

> it explains why the youtube version of your song feels just a little more 'lifeless' than the high quality version you have elsewhere

Having hearing sensitivity over 16 kHz is unusual. If you're under 15 years old and kept your ears pristine by not listening to loud noises, you might be able to hear it. Older people are out of luck.

Moreover, even if you can hear above 16 kHz in loud pure tones, there is so little content in real audio/music above 16 kHz that it makes no practical difference.

> massive savings ... effectively saved 25%

Not really. Going from a 48 kHz sampling rate to 32 kHz is indeed 2/3× the size for uncompressed PCM audio. But for lossily compressed audio? Not remotely the same. Even in old codecs like MP3, high frequency bands have heavy quantizers applied and use far fewer bits per hertz than low frequency bands. Analogously, look at how JPEG and MPEG have huge quantizers for high spatial frequencies (i.e. small details) and small quantizers for broad, large visual features.

[naltroc]

It is true that your ears do not perceive the higher frequencies in the same way (through pitch detection). However, if you put on a headset and apply only frequencies above 16kHz, you will distinctly notice a change in the pressure in your headset's ear cups.

Good point about the savings. I was using uncompressed format as the reference, but it is indeed unlikely that YouTube serves out lossless audio.

I also should have used the word "delivery" instead of data storage. Those are two separate problems: where the original asset is stored (and how, if they don't store raw originals), and also how the asset is delivered over the web.

[danadam]

> When I use an FFT to view the spectrogram on YouTube music videos, it is very obvious that YouTube applies a lowpass filter at 16kHz on all videos (true since 2023 at least).

Maybe with a browser that doesn't support Opus and gets AAC instead (Safari?). With Firefox or Chromium on Linux I get up to 20 kHz, which by design is the upper limit in Opus codec.