5th Gen classic beeping when high frequency sounds are played in songs.

[dusk robin]

Hey there, fairly new to the hobby.
A couple of days ago I purchased a 5th Gen iPod classic, loaded some songs into it and today I noticed that when certain high frequency sounds are played in a song the iPod plays a beep in one ear, sometimes the right sometimes the left.
I can't figure out what this is, I tried listening to the songs which have this beep noise on my computer (the exact same file with the exact same pair of headphones) and it wasn't there. It still plays when using other pairs of headphones which means this is an iPod problem and not a headphone problem. I also tried deleting and downloading the songs and the problem wasn't solved, after all of these fixes didn't work I tried to restore and download the songs again and it didn't help.
I would really appreciate any help.
Thanks.

[rapid vault]

I have never heard about this kind of issue. Please try to record it somehow using another microphone and let us hear the original and distorted fragment.

[dusk robin]

You can here these noises pretty clear in this recording, make sure to watch out for your volume

[dusk robin]

And here is a recording of the exact same song and file playing from a macbook through the same pair of headphones (recording starts at about 0:05).

[rapid vault]

Those are clearly audio decoding issues. Performance issues (file compressed the way it requires too much processing power for 5Gen - if clicks show in different places each time) or some specific way it has ben compressed/encoded, that makes the built in decoding/deompression engine intepret it incorrectly (if clicks are always in the same place).
IDEAS:

• Take the file from a different source and/or create it on your own from the source media.
• Check it using correspondig file stream checker (there are available both for MP3 and FLAC) - maybe there is file structure issue that is correctly "covered" by mor advanced codec in the computer
• recompress the file you have into different format - or even the same, but making sure the file will be uncompressed to wav and pushed back through the codec. This is the worst option (especially for already lossy compressed files) as for sure you will loose some quality.

[dusk robin]

First of all I really appreciate your help...
I went straight into trying to fix the file for one of the songs which had the beeping noises and it fixed most of it and added a couple of more small beeps at the beginning. For another song I couldn't find the exact file I added to itunes so I went on youtube and downloaded the same song from another profile and when I synced it to my ipod and played it the beeping was gone so I will try that with a couple more songs before deciding which way is the right one.

[stuck saffron]

that sounds clearly as glitches on the decoding or encoding, here I see somebody talked about using 2010 m4a encoding for the ipod

btw what's that song, sounds really good

[short crater]

something about the perceptual noise reduction that the iPods don't like

older iTunes doesn't do it

and no you can't use FFmpeg AAC to get around it that does the same thing

[dusk robin]

Do not fire by madvillain🙃

[dusk robin]

Changing the download source fixed it for this example, next time I’ll come across a song that does the same thing I’ll try changing it again

[stuck saffron]

yooo! nice discovery I know MF doom but didn't know that demos album

[dusk robin]

Super cool album, you should check it out and if you like this stuff definitely try getting into some of madlib’s stuff

[dusk robin]

Just coming back to update, I found the same problem with a couple other tracks so I deleted the original file and downloaded the same tracks from different sources and the problem was fixed.

Edit: It wasn't.... F me

[stuck saffron]

happened with mp3 format too?

or only on AAC?

[dusk robin]

Mp3 and m4a

[stuck saffron]

🤔 is flash modded? if so could be the SD card going bad

[dusk robin]

Original hard drive. I ordered an iflash solo for it, not for that reason but that might help. I don't think that's the reason, it is very present in 2 certain albums which were not downloaded in one after the other and they are from 2 different artists.

[bleak raptor]

I’ve had this issue before too and @rapid vault is on the right track w the suggestions. I don’t know the encoder settings offhand but I think you can re-encode to get the beeps / chirps to go away. If they don’t show up when using a computer/phone that’s a good signal it’s the combo of encoding and iPod, trying to encode again w ffmpeg or iTunes seems like a good approach

[short crater]

it has something to do with some AAC codec settings that got updated in the new encoders

inurayama did a whole thing on it, iirc tldr is PNS (perceptual noise substitution) which is normally supposed to boost efficiency of the codec ends up introducing artifacts

FFmpeg AAC says not to disable it (I'll do some more testing if you remind me in like 9-10 hours) but if you're syncing with iTunes just change iTunes versions to an older one

[short crater]

and these artifacts only show up on iPods because the PNS settings only meaningfully affect the ancient decoder in the iPod

they do things with newer encoders but that thing is Not bleep and clip

[bleak raptor]

Ooh interesting, do you have a link or something to the inurayama thing? I’d be interested to learn more

[bleak raptor]

🙏

[dusk robin]

I think it definetly has something to do with the codecs. Today I changed some of the files which had this issue to another codec, from m4a to mp3 320kbs and it solved the issue completely for those files. The same issue popped up in other files today so tomorrow I will try to change those to mp3 320kbs aswell and will come back with the results. I'd like to thank you again for your help @rapid vault, @bleak raptor, @short crater and @stuck saffron .

[rapid vault]

Thanks for confirmation, this is as valuable as our diagnosis above.

[stuck saffron]

aight, good luck with that

[dusk robin]

Another update, I replaced the corrupted m4a files with 320kbs mp3 files and the noises disappeared.

[dusk robin]

The story never ends... there seems to be another problem, the files that i replaced to mp3 320kbs now won't play until the end of the song, they cut halfway through and skip to the next. This is an issue that I experience solely in the files that I replaced.