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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
    I don't think you understand (or maybe I don't). AptX is a codec, not a container. The whole idea of an ABX is that you are not supposed to know what is being tested. So in order to test aptX vs aac, you need to switch between two different sources. The only way to do this is sighted, so you can't abx using Foobar.
  2. shortwavelistener
    Of course AptX is a container. And I did actually ABX on different sources. Sometimes i played music from my iPhone via BT AAC and compared them to my Mac playing music via aptX.

    Oh.. And it's evening so i need to rest..
    Last edited: Jul 21, 2018
  3. Brooko Contributor
    So you didn't actually ABX (aac vs AptX) and you didn't use Foobar. And you can't have volume matched. Thats all i wanted to establish.

    And AptX is a codec - not a container. You can't have an AptX file. They don't exist.
  4. shortwavelistener
    Of course I know AptX is a codec. I know that already, ever since it was first came out in 2012 as a new standard for A2DP. (Isn't AptX invented in the 80s? I had to find out more)

    BTW, thanks for the information though.

    Of all audiophiles here on Head-Fi, you deserve some respect bro! :o2smile::ok_hand::thumbsup:
    Last edited: Jul 21, 2018
  5. bigshot
    Can you explain to me what "better transparency" sounds like to human ears? Transparency is transparent, isn't it? If there was room for improvement it wouldn't be transparent.

    It seems to me that if certain equipment is presenting a transparent sound source as not transparent, there is probably something wrong with the equipment, not the transparent sound source.
    Last edited: Jul 21, 2018
  6. PiSkyHiFi
    Let me guess, you read somewhere that AAC is audibly transparent to human ears, so you're going to stick with that and make everything else follow from it... I'm guessing that's what's going on.

    What if I just said to you straight out that any lossy codec is by definition, not transparent. Apple might say to you, it's audibly transparent, so you can feel safe that no one else is getting better sound than you even if they have something different, but that's just them drawing the line for you.

    I draw the line at FLAC over Bluetooth... lossless transmission means digital transparency, it's then up to the analog stages to make it sound accurate from there.

    Until we have that, we can argue over bit-for-bit - which is digital transparency, which neither AAC nor AptX HD provide.

    AptX HD is useful because the bitrate is now getting up to a reasonable percentage of Redbook CD quality, so it doesn't have to be as clever a protocol to be more transparent in the digital realm as AAC, because it stipulates a higher bitrate and depth.

    If AAC could be used at 576 KBps rather than AptX HD, I'd prefer that, but it's not low latency either, so I'd prefer the Bluetooth codec that is audibly transparent, minimally digitally transparent and low latency.

    LDAC is here, that's another choice that's better than AAC for Bluetooth, just for the bit depth and rates alone.

    When lossless can be easily transported over Bluetooth, this discussion about transparency will be moot.
    Last edited: Jul 21, 2018
  7. bigshot
    You're in the Sound Science forum. We test things here! This issue is very important to me. I have a very large collection of music- tens of thousands of CDs, and even more records. I built a media server in my theater to serve up both movies and music. The server now contains nearly 100 TB of storage, and over a year and a half of music.

    Before I embarked on digitizing my collection, I decided to test three major codecs... Fraunhofer MP3, LAME MP3 and AAC. I researched [/SIZE]artifacting. There used to be a very good page on the web with examples dedicated to cataloguing the various ways compression artifacts could occur and what the artifacts sounded like. I pulled dozens of titles from my collection from various genres, from classical to century old acoustic recordings to jazz, acoustic music, electronic music, examples from the 20s, 30s, 40s, 50s... all the way up to the most current recordings in my collection. I included digitized Sheffield Lab direct to disc LPs and downsampled high data rate audio. And I digitized each title at 128, 192, 256 and 320 CBR using each one of the three codecs.

    I went over the samples with a fine tooth comb comparing it head to head with lossless, searching for artifacts. If I found one on any music sample, I eliminated that codec and data rate from further consideration. When I was done, I found that Fraunhofer 320 was *almost* transparent, but I had one CD that could make it artifact slightly. LAME MP3 was perfectly transparent at 320. And AAC was transparent at 256. I chose AAC 256 VBR as my standard setting for my music server. It took nearly two weeks full time, but it was worth it to me because I didn't want to have to ever go back and re-rip or re-encode any of my collection. I now have a massive digital library and I listen to it all the time. I have never encountered any artifact on any of the hundreds of thousands of files.

    In addition to my own collection, I'm a digital archivist in charge of a large media library that belongs to a non-profit educational organization. I know a little bit about this stuff. If I was maintaining a master file- the original recording master- I would keep it in whatever format that it was created in. That way if the file needed to be remixed or edited, it would be completely flexible. But for reference files- or more specifically, files of music I listen to in my living room- compressed audio is perfectly fine as long as it's audibly transparent.

    The definition of "audibly transparent" is that a copy sounds *exactly* like the original. There's no such thing as "better sounding" than transparent. There's only larger file sizes. Bigger file sizes may have a purpose if you are working in a recording studio, but for the purposes of listening to music in the home, compressed audio that meets the threshold of transparency is as good as you can get.

    You can't judge sound quality by the data rate. Every codec has a different point of transparency. Some are more efficient than others.
    Last edited: Jul 21, 2018
    rule42, Jearly410 and Brooko like this.
  8. PiSkyHiFi
    I'd need to do an in-depth statistical analysis, or I could use some simple math tricks to help guide me through this, basically the encoder would have to start being really stupid if you are using more bandwidth and approaching a decent percentage of the uncompressed required bandwidth.

    16 bit depth 44.1 KHz is a 1.4Mbps stream - that's the uncompressed required bandwidth.

    Compressed losslessly, you can achieve around 800 to 900 KBps - assuming Redbook and fast hardware.

    So, compressing with 576KBps lossy is now approaching this point.

    So, now we're comparing quality of lossy codecs that are approaching a point where their respective psycho-acoustic comparisons are becoming meaningless.

    AptX and AptX HD are transmission protocols and they will be redundant soon enough.

    AptX HD is mathematically better than AAC when comparing 576KBps to 256b KBps, there just isn't any need to debate that.

    I once stored my entire collection as 192 KBps MP3 until I could afford the equipment that revealed my mistake. I used to encode to AAC in M4A files for portable use, but now I can store all my FLACS in my phone... lossy is nearly dead for me.
  9. bigshot
    I'm talking about sound quality, not math. Bigger numbers don't automatically mean better sound. The codec has an impact on the quality of the encoding as well.

    Would you like to hear one of my sample files for yourself? I can send you either a FLAC or ALAC. It has ten different samples, all the same music. The samples consist of Frau, LAME and AAC and 192, 256 and 320. One of the samples is lossless. You tell me which one is which. I'll tell you how you did. Then we'll talk about what codec and bitrate is necessary to achieve transparency. (Hint: Redbook is overkill)

    By the way, 192 Fraunhofer MP3 is not transparent. If you asked me before you started encoding your library, I would have told you to use LAME 320 or AAC 256.
    Last edited: Jul 21, 2018
    shortwavelistener likes this.
  10. PiSkyHiFi
    No, until we're comparing analog stages. we're talking math.

    No, I don't want to hear on of your samples. I'm sure it took lots of work to get them - I've been there. It's approaching time to forget about the drawbacks of lossy and even bothering to compare them.

    Equipment quality is the main reason I don't like lossy, it doesn't give you a chance to reconsider your options when you may simply need better equipment to tell the difference.

    If you believe redbook is overkill, then you need to try better sound equipment, because it isn't and the purpose of saving space is no longer required.

    We all have our own thresholds - redbook is enough for me, but no less.
  11. bigshot
    There are no drawbacks to lossy if there is sufficient bandwidth to achieve transparency. I think the problem is that you don't understand what transparent means. It means perfect for human ears. Indistinguishable from the source. The source can be redbook or 24/192, it doesn't matter. If it sounds the same, for the purposes of listening to music on your system, it *is* the same. You can count beans and pick the one with the most beans, but it won't be any improvement in audible sound quality. And a codec works just as well for a cheap system as it does a high end one. The limiting factor is your ears. Perfect for human ears is as good as you are ever going to hear in your whole life.

    The reason you don't know about transparent compressed audio is because you refuse to listen to it. That is perfectly fine. A nice full hard drive might be comforting when you go to sleep at night. But it doesn't mean that you have better sound quality. Just bigger files. You just don't have any experience in this area.
    Last edited: Jul 21, 2018
  12. PiSkyHiFi
    The reason I don't know about lossy....

    Sorry mate, but you can stick your condescension.

    It's just that now that we've hit the point where its just no longer needed.

    If you've been through which lossy codec like I have, it should be good to know they can be dispensed with completely.

    Bluetooth is the last bastion for lossy.
  13. shortwavelistener
    Well except for aptX HD and LDAC, which is strictly ADPCM and therefore it does not utilize any form of psycho-acoustic models.
  14. PiSkyHiFi
    My point isn't about their respective psychoacoustic models or lack thereof.

    My point is that the bit rate is high enough to pay less attention to the intricacies of each codec, since the overwhelming data rate reduces it's influence.
  15. shortwavelistener
    Oops, sorry. Again I misinterpreted your statement regarding bitrates of BT codecs.
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