(https://s25.postimg.cc/cfddvdqa3/original_2448.jpg) (https://postimg.cc/image/cfddvdqa3/)
original 2448 wav
(https://s25.postimg.cc/d4w67qj3v/purchased_itunes_aac.jpg) (https://postimg.cc/image/d4w67qj3v/)
purchased itunes plus aac
(https://s25.postimg.cc/5owwlxfyz/itunes_converted_plus_aac.jpg) (https://postimg.cc/image/5owwlxfyz/)
converted to itunes plus aac from 2448wav
(https://s25.postimg.cc/n2770sizv/qaac_44.1_bats127.jpg) (https://postimg.cc/image/n2770sizv/)
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?
Music you buy on iTunes is provided by the artist or music company, not necessarily encoded the same way as iTunes.
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.
"original 2448 wav": How do you know it is the same mastering? (Are you the artist and uploaded that file to iTunes?)
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