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iPhone AAC vs. Aptx and Aptx-hd real world

Discussion in 'Sound Science' started by neil74, Oct 4, 2017.
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  1. bigshot
    Not likely. The difference between 19kHz and the upper limit of human hearing is a small fraction of a note on the musical scale. Most people over 30 can't even hear up to 19kHz. And it doesn't matter anyway, because recorded music doesn't generally have any audible content up there anyway.
     
    pstickne likes this.
  2. Vin60
    You are absolutely right - I personally do not hear 20khz. However downsampling means not only the cap in khz, but degrading details as well, as otherwise it would be too simple.
     
  3. bigshot
    Have you tested to find out what your threshold of transparency is for various codecs and data rates?
     
  4. Vin60
    Not sure I understand - Hz do not differ from data rates nor codecs. If you mean do I hear difference between Mp3 256 and Mp3 320? - some times yes, some times no, and I do not hear any difference between .flac and AAC 256
     
  5. bigshot
    You mentioned that you heard degrading of details, I was just curious where your line of transparency was where there is no degradation any more.
     
  6. shortwavelistener
    Actually, that's because Airplay encodes the audio stream in ALAC (the same goes to it's predecessor, the Airport Express too). Since ALAC is a lossless format just like FLAC, so Airplay will retain all the information of the audio file, regardless of the type of audio file played from the source.
     
    Last edited: Oct 30, 2018
  7. bigshot
    I didn't know that! Thanks!
     
    pstickne likes this.
  8. Vin60
    Its really depends on content, but I’m sure everyone can hear difference between mp3 128 kbps and mp3 192 kbps. Keeping in mind android encodes in aac over bluetooth in less then 128 kbps mp3 quality (I presume its 96kbps) android users should definitely stick to aptx or its higher equivalents
     
    pstickne likes this.
  9. AKGForever
    What does "Mastered for iTunes " mean when the source was originally recorded in analog? Unfortunately I found nothing in the Apple description saying that the source has to be from original source material. CDs and AAC made from sources made in the 1960s through the 1980s are all over the place quality wise. Some of it is poor recording techniques but a lot of it is because the masters are multi-generational. I also find that compilations, especially those from various artist, tend to be of poorer quality and from a mult-generational source.
     
    Last edited: Oct 30, 2018
  10. bigshot
    All content distributors are at the mercy of what master the label pulls off the shelf. And "best ofs" and compilations are going to tend to be a hodgepodge of sources.
     
    Last edited: Oct 30, 2018
  11. pstickne
    I found https://www.soundguys.com/understanding-bluetooth-codecs-15352/ interesting. Some points:
    - Bluetooth AAC is highly dependent on the specific encoding stack's implementation (and pre-encoded AAC do not appear to be sent "as they are"). It is effectively only [almost] "CD quality" on iPhone devices. Naturally, it will never have more information that the original source.
    - Bluetooth AAC is psychoacoustic whereas aptX is not - so AAC is more akin to an inline 'conversion to MP3' (offending anyone a bit? :D). This is also why AAC requires more power/processing than SBC/aptX and why comparing 'Bluetooth transmission bitrates' between different protocol can be misleading.
     
    Last edited: Jun 10, 2019
  12. pstickne
    It's a shame really, as the DSD encoding was designed as an alternative/improvement to PCM encoding. Excluding licensing opportunities and the like, one reason was to make hardware simpler and cheaper. (And there isn't anything wrong with that goal.)

    It's the re-introduction as a "Hi-Fi" badge as opposed to data representation format that is the gimmicky bit - higher numbers is better? I guess one can always covert CD (eg. "a" PCM encoded source) to DSD and call it a day.. same data, different pattern of bits.
     
    Last edited: Jun 10, 2019
  13. djyang0530
    ios only support aac and aac and aptx has a huge differncen since aptx can send 16/44.1
     
  14. pstickne
    Uhh, AAC “can send” 16/44 as well. However, such statements add little to no value as discussed in https://en.wikipedia.org/wiki/Audio_bit_depth Remember that both AAC and aptX are lossy and neither is PCM; one has to look at the quality of the resulting decoded (PCM, DSD, whatever) signal**.

    Also, AAC is arguably a more transmission-efficient codec (for human consumed audio) as it utilizes stronger psychoacoustic principals so even looking at BT wire bandwidth usage can be very misleading.

    **As noted previously, there is a wide range of differences in the quality of AAC encoders, with many Android implementations being subpar.
     
    Last edited: Jun 20, 2019
    SteveOliver likes this.
  15. castleofargh Contributor
    https://habr.com/en/post/456182/

    I don't know enough to say if everything in this article is correct, but the little I know seemed to align.
    it certainly is very informative.
     
    pstickne likes this.
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