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Topic: The problem about itunes from wav 48 to plus aac 44.1 (Read 300 times) previous topic - next topic
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The problem about itunes from wav 48 to plus aac 44.1


original 2448 wav

purchased itunes plus aac

converted to itunes plus aac from 2448wav

qaac:--ignorelength -s --no-optimize --no-smart-padding --threading -r 44100 --native-resampler=bats,127 -v256 -q2

I convert the original 2448 wav to a itunes plus aac in itunes 12.7.5.9,but the high frequency above 19K of this aac was cutted mostly.But the purchased itunes aac didn't appear this problem.
I convert the original 2448 wav to a "-r 44100 --native-resampler=bats,127 -v256 -q2" qaac aac,the problem didn't appear.
The problem exist many years..is it a bug in iTunes?Apple forget to set the resampling quality of 48 to 44.1?

Re: The problem about itunes from wav 48 to plus aac 44.1

Reply #1
Music you buy on iTunes is provided by the artist or music company, not necessarily encoded the same way as iTunes.

Re: The problem about itunes from wav 48 to plus aac 44.1

Reply #2
Probably I-Tunes chops off everything above 19kHz by default for lossy conversion, because it may improve the overall-quality of lossy conversion.

That isn't really an issue. If you don't want it, try to disable that or just use different way to convert. But I would recommend the way through I-Tunes because there is almost nothing useful between 19-22kHz. There are a few very subtile overtones drown in noise and resampling artifacts. But if you disable that, precious bit-rate is wasted for that frequency range.

And remember: You have a heavily overcompressed record (the green waveform is a solid brick with no dynamics). If you resample that, the peak level is likely to be raised much so heavy clipping might occur. Lowering the gain by -3dB should be the easiest way to prevent that. It is always better to lower the gain of such recordings by a few dB before lossy conversion because the conversion raises the peak level a bit once more.

This could be the reason, why you get different results. Clipping means distortion and distortion means overtones.. and the clipping appearing after conversion is happening during decoding - after the lossy "bottleneck" ;-).

Probably, I-Tunes is doing that gain reducing or some limiting for you. On the command-line way you have to do it manually.
- I abandoned this account since I didn't find a way to delete it -

Re: The problem about itunes from wav 48 to plus aac 44.1

Reply #3
"original 2448 wav": How do you know it is the same mastering? (Are you the artist and uploaded that file to iTunes?)

 

Re: The problem about itunes from wav 48 to plus aac 44.1

Reply #4
Probably I-Tunes chops off everything above 19kHz by default for lossy conversion, because it may improve the overall-quality of lossy conversion.

That isn't really an issue. If you don't want it, try to disable that or just use different way to convert. But I would recommend the way through I-Tunes because there is almost nothing useful between 19-22kHz. There are a few very subtile overtones drown in noise and resampling artifacts. But if you disable that, precious bit-rate is wasted for that frequency range.

And remember: You have a heavily overcompressed record (the green waveform is a solid brick with no dynamics). If you resample that, the peak level is likely to be raised much so heavy clipping might occur. Lowering the gain by -3dB should be the easiest way to prevent that. It is always better to lower the gain of such recordings by a few dB before lossy conversion because the conversion raises the peak level a bit once more.

This could be the reason, why you get different results. Clipping means distortion and distortion means overtones.. and the clipping appearing after conversion is happening during decoding - after the lossy "bottleneck" ;-).

Probably, I-Tunes is doing that gain reducing or some limiting for you. On the command-line way you have to do it manually.

but the 96 to 44.1 in iTunes don't cut so much high frequency...
http://picto.ml/images/2018/07/10/96wav-to-itunes-plus-aac.jpg
http://picto.ml/images/2018/07/10/9624wav.jpg

 
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