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Thread: ALAC 16bit vs. 24bit Reversed waveform polarity

  1. #1

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    Jun 2017
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    Question ALAC 16bit vs. 24bit Reversed waveform polarity

    I came across this problem while converting hi-res *.wav tracks into 24/48 ALAC files. This is what I found: encoding an audio file into ALAC 24bit results in a reversed waveform polarity, which comes back to normal once converted back to *.wav, *.flac or even ALAC 16bit. I have been experimenting with both dBPowerAmp and DVD Audio Extractor. The software doesn't change the result.

    Do you know what is causing this? I don't think it's normal.

  2. #2
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    Re: ALAC 16bit vs. 24bit Reversed waveform polarity

    If when you decode the ALAC to wav (that is simply decompressing the audio) and the polarity is correct, then it was correct in the ALAC file.

    How are you determining that the polarity is inverted?

  3. #3

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    Re: ALAC 16bit vs. 24bit Reversed waveform polarity

    Quote Originally Posted by Spoon View Post
    If when you decode the ALAC to wav (that is simply decompressing the audio) and the polarity is correct, then it was correct in the ALAC file.

    How are you determining that the polarity is inverted?
    I can determine the correct waveform polarity by ripping the file first in wav and flac formats, then compare the results with the alac file.

    By ripping in alac 24bit and then converting to wav, the polarity goes back to normal (as you suggested to try).

  4. #4

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    Re: ALAC 16bit vs. 24bit Reversed waveform polarity

    Quote Originally Posted by Spoon View Post
    If when you decode the ALAC to wav (that is simply decompressing the audio) and the polarity is correct, then it was correct in the ALAC file.

    How are you determining that the polarity is inverted?
    Even if the conversion wav 24bit --> alac 24bit --> wav 24bit gives back the correct polarity, it doesn't necessarily mean that the alac file is encoded with the correct polarity. A null test between the wav file and the encoded alac returns in pure silence.

  5. #5
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    Re: ALAC 16bit vs. 24bit Reversed waveform polarity

    >Even if the conversion wav 24bit --> alac 24bit --> wav 24bit gives back the correct polarity, it doesn't necessarily mean that the alac file is encoded with the correct polarity.

    It does, if the ALAC file had the wrong polarity, then it would decode to wave with the wrong polarity. There is no inversion going on from ALAC to Wave which would correct the polarity if it was wrong.

    It is likely the tools you are using to test the polarity have the issue, not the file its self.

  6. #6

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    Re: ALAC 16bit vs. 24bit Reversed waveform polarity

    Quote Originally Posted by Spoon View Post
    >Even if the conversion wav 24bit --> alac 24bit --> wav 24bit gives back the correct polarity, it doesn't necessarily mean that the alac file is encoded with the correct polarity.

    It does, if the ALAC file had the wrong polarity, then it would decode to wave with the wrong polarity. There is no inversion going on from ALAC to Wave which would correct the polarity if it was wrong.

    It is likely the tools you are using to test the polarity have the issue, not the file its self.
    You're right. It's my version of Audacity that needs to be updated! The file is fine.
    Cheers

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