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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. Brooko Contributor
    Hillariously funny = the guy who wrote it is a producer and engineer, and knows more about the topic than most people here. He's worked with Grammy award winners and owns his own studio.

    I won't engage with you - if this is the sort of trolling response I get. But I will state categorically - you are incorrect in your assumptions, and quite frankly you're making a clown of yourself in the approach you are taking. I suggest you go to the thread I linked and try and tell Greg his post is BS. I'm subscribed to that - so it will be an interesting conversation I think.
  2. PiSkyHiFi
    Go ahead mate, the math speaks for itself.... I couldn't care less about some blokes reputation if he has math errors....

    This dude you refer to speaks of the entire dynamic range of some music being 12 dB !!

    Talk about laughable...
    Last edited: Jun 17, 2018
  3. PiSkyHiFi
    I can't even begin to fathom why people would argue math... if you're reading this, do some research elsewhere, head-fi isn't a source.
  4. PiSkyHiFi
    Mathematically, AAC is superior encoding at the same bitrate to any other lossy codec.

    That's the end of it though, increase the bandwidth and bit depth and you'll do better than not losing anything as the information rate increases.

    This is self-evident - nothing to do with bit depth being ignored by a Fourier or discrete cosine transform in floating point. (sorry, can't do a discrete transform on FP data, I mean DCT on higher bit depth representations.)

    The real question is really how much more accurate/inaccurate is AAC than AptX HD at Bluetooth 5.0 specs
    Last edited: Jun 17, 2018
  5. castleofargh Contributor
    while they're non PCM codecs, we still need some sort of easy reference for what the extracted signal will contain. I agree that it's not the proper expression of resolution for non PCM signals, but if we don't use that, what else do we have? the bitrate can be even less relevant when different compression codecs are being used. so there is not much of an option, we either know all about each codecs involved, or we use the PCM equivalent they give us(with the hope that they're not misleading us too much).

    now, and this is only my opinion, I have a hard time taking any so called high res BT seriously. I have yet to use a BT headphone that wouldn't have audible background hiss when I'm in a quiet room. so 24bit or 16bit equivalents for the signal, I couldn't care less when I'll still get plain old hiss some 50 to 70dB below signal depending on how loud I listen to my headphone.
    and that's without including ambient noise at all.

    they tried to explain to you why your math is not necessarily a direct translation into fidelity. objective or subjective. math is not the issue here. taking one variable and deciding that it's the reliable one to quantify fidelity, it already can be a difficult thing to do with PCM signals sometimes. so with lossy codecs and streaming requirements, there is nothing wrong with trying to look at the whole picture, and maybe try to measure the output of some gears while using various solutions(if we're lucky to have them on the same devices).

    that said, I believe we have enough topics already where we can all go in circle with partial views about the audio chain and which variable is strongest animal in the fidelity jungle for whatever reason. I don't believe this topic needs to turn into one more of those mud fights. we've been trying to get a clearer picture about what each BT codec really does and I'd love to keep it that way.
  6. PiSkyHiFi
    My main issue for BT headphones is that they probably don't have the DAC or analog stage to match what the BT data rate can achieve when using AptX HD - that is the whole point though, it's headroom to help remove digital error from the reproduction, especially because it's lossy still.
  7. PiSkyHiFi
    AptX HD is also used as a transmission protocol for multi-room wireless speakers, I sincerely hope Bluetooth achieves lossless with varying transmission rates in future.

    When that happens, we can all dump on AptX HD objectively (and AAC)
  8. Brooko Contributor
    Evidently you skimmed the post. What Greg said is that some music has dynamic range of as little as 12 dB. The recordings with the highest DR is mainly classical and rarely goes above 60 dB. So he's given you a common set of numbers (min and max) for DR in most recordings (~12-60 dB). Whether you like it or not - he is the expert in this field.

    Rather than paraphrasing - here is the pertinent part:

    I'm really not sure why you are so aggressive with this.
  9. PiSkyHiFi
    Why did you underline some music ? It seems to me you didn't read my post.

    Whether he likes it or not, extracting 150 dB from a 96dB source is complete BS - error diffusion, interpolation, whatever, you can infer a little more with correct mastering, but it tails off pretty quick - a lot quicker than achieving 120 to 150 dB.
    I think he is trying to refer to aliasing present in PCM and using either a decent high pass filter or mathematical equivalent to help eliminate it.
    I tell you what does achieve 120dB without skipping a beat, 24 bit source.

    The superiority of classical music ???? unbelievable bias. Maybe he means discerning a lot of combined waveforms, probably should say that.

    Music doesn't go above 60dB dynamic range?.... I feel people here are just plain digging holes for themselves, do they mean a midi interpretation of a piece... I can't even wrap my head around the intended meaning.
    What about the sound.... that's actually the music too.

    It's a reasonable article, with some obvious errors here and there, but it doesn't change anything to do with AptX HD, AAC and PCM.
  10. neil74
  11. PiSkyHiFi
    Ahh, I hadn't hard of this until now...

    Looks like its the replacement for vorbis

    I stand corrected, thanks for the info!
  12. PiSkyHiFi
    I'm just going to leave this quote from Wikipedia about dynamic range:

    "In 1981, researchers at Ampex determined that a dynamic range of 118 dB on a dithered digital audio stream was necessary for subjective noise-free playback of music in quiet listening environments."

    That is the number that concurs well with my understanding, despite coming from 1981.
    There does seem to be conflict about it in general, I guess because terms need to be clearly defined regarding what's being measured.
  13. Brooko Contributor
    The quote was talking about recording - not playback (its available in the AES library).

    Here's the part they were talking about:
    And if you take the noise floor (about 30-40 dB in a quiet recording environment), then the microphones would need to have that sort of dynamic range to be able to record the lowest and highest audible sounds. Or in other words 30dB (noise floor) + 80-90 dB as safety to reach peak. It still means the actual DR of even well recorded music is still going to max out at around 60-70dB (well within the 16bit window for playback).
  14. PiSkyHiFi
    I'm not talking volume range when I discuss dynamic range, it could be interpreted that way, but I'm discussing audible precision, which means that despite the human ear attenuating hearing a range of loud sounds or a range of soft sounds, but not both at the same time, the sound reproducing device needs the full range of at least 100dB, plus some room for some people's ability to focus on aspects of the precision that aren't obvious, like interferometry - humans can actually locate objects using this to a degree, combined with straight volume difference between ears. So spatial sense is very sensitive to precision changes.

    You mention noise floor - so I'm working with a value of 0 dB, which is defined to be the audible threshold of an isolated tone.

    Good old tape decks achieve up to 90dB precision, apparently up to 110dB with Dolby and the difference is audible.

    Equipment I use needs to be above 110dB in precision or I can tell it pretty quickly. That's just from experience and looking at that specs of things I try.

    I much prefer the solid noiseless sound of an ESS 9018 to the sound of a Wolfsen WM8740 for example, the precision difference is audible. Some say the 9018 is too dry... probably because of the complete lack of any audible noise replaced with tight precision. I love it.
  15. castleofargh Contributor
    look I really do not want this plague of a discussion to ruin yet another topic. please take it to a topic about human hearing, bit depth, dynamic or whatever it is you're trying to say. we can probably find a dozens of those topics still open on Headfi, so pick one if the subject really interests you and maybe link your answer in here so that the few who care, can go there and follow up on the discussion.
    if you find a BT headphone with "110dB in precision"(whatever that means) at your usual listening level, maybe I'll reconsider all this as being relevant to this topic. then I'll probably go and buy that headphone. ^_^
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