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Thread: Converting an AAC Mono file to AAC Stereo, higher audio bitrate?

  1. #1

    Default Converting an AAC Mono file to AAC Stereo, higher audio bitrate?

    I hope someone can help with this issue. A client is sending me videos recorded with iPhone; with dual-channel MONO AAC-LC audio, an average of 89 kbps. It's mono but dual-channel. I'm editing with Premiere Pro, and on export, I choose H.264 with AAC-STEREO. (I guess it does not change anything it's still a mono duplicated in both channels?) But I'm choosing Stereo because I'm also using another short Stereo AAC 192 kbps track in the same project, although 90% of audio in this project is 89 kbps.
    The question is:

    • Should I keep the closest bitrate on export (96kbps) or upsample to 192kbps if I choose Stereo on export, or because of that other audio. Just want to keep best possible quality and not sure if upsampling is beneficial or it could degrade the quality of 89kbps audio?

    Export have to be in AAC format, so please don't suggest to convert to another format. Thanks!

  2. #2

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    Up-sampling doesn't do anything noticeable to the sound. Down-sampling might make some noticeable difference to the file that's originally higher bit-rate.
    Depending on how important that one piece of 192kbps is I would chose either that or down-sample it all to 96kbps if it's not too important.
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  3. #3
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    Quote Originally Posted by Grapes View Post
    Up-sampling doesn't do anything noticeable to the sound. Down-sampling might make some noticeable difference to the file that's originally higher bit-rate.
    Depending on how important that one piece of 192kbps is I would chose either that or down-sample it all to 96kbps if it's not too important.
    Agreed - assuming it's for delivery. However, as I understand it (and this comes from a music producer friend of mine many years ago so I'm happy to be corrected) if you are performing any sort of processing on the sound (noise reduction, EQ, mixing with other audio, anything) you should do this at the highest sampling bitrate you have available. Grape - interested in your take on this.
    Tim

  4. #4

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    Quote Originally Posted by TimStannard View Post
    Agreed - assuming it's for delivery. However, as I understand it (and this comes from a music producer friend of mine many years ago so I'm happy to be corrected) if you are performing any sort of processing on the sound (noise reduction, EQ, mixing with other audio, anything) you should do this at the highest sampling bitrate you have available. Grape - interested in your take on this.
    Interesting point Tim. It sure sounds convincing. I assume that if you are processing the sound, you want the changes to be as good as possible. A bit similar to for example the quality level of some blur effects. I doubt however if it would make sense to go over 192kbps when processing the sound in this case seeing as that is the highest used bitrate in this case.
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    Quote Originally Posted by Grapes View Post
    Interesting point Tim. It sure sounds convincing. I assume that if you are processing the sound, you want the changes to be as good as possible. A bit similar to for example the quality level of some blur effects. I doubt however if it would make sense to go over 192kbps when processing the sound in this case seeing as that is the highest used bitrate in this case.
    Indeed, I should have said the highest source rate you have available.

    I think the logic goes thus: I'll use frequency rather than sampling rate as it's easier to come up with an easily understandable example.

    Assume, for the purpose of illustration, the upper limit of human hearing is 20kHz
    You have a signal that includes tones (harmonics) of 30kHz
    There is no point delivering material with anything above 20kHz

    However, if you are processing the signal it makes perfect sense to have those inaudible tones available.
    Imagine you are applying processing that involves halving the frequency of the sound. Your 30kHz tones are now 15kHz - within the audible range.

    (Of course you might not want these, but at least you are now able to make a choice)
    Tim

  6. #6

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    Quote Originally Posted by TimStannard View Post
    Indeed, I should have said the highest source rate you have available.

    I think the logic goes thus: I'll use frequency rather than sampling rate as it's easier to come up with an easily understandable example.

    Assume, for the purpose of illustration, the upper limit of human hearing is 20kHz
    You have a signal that includes tones (harmonics) of 30kHz
    There is no point delivering material with anything above 20kHz

    However, if you are processing the signal it makes perfect sense to have those inaudible tones available.
    Imagine you are applying processing that involves halving the frequency of the sound. Your 30kHz tones are now 15kHz - within the audible range.

    (Of course you might not want these, but at least you are now able to make a choice)
    Exactly
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