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Should i convert to 256 kbps aac on itunes

Discussion in 'Sound Science' started by dubmonger, Jan 7, 2013.
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  1. bigshot
    He said the bass levels were different, didn't he? Maybe it's Sound Check. ITunes might not have had a chance to scan one of the files.
  2. jaddie
    Yes, there was a comment on lack of bass, but of course, just transcoding or encoding wouldn't do that by itself.  
    In my tests at least, Sound Check wasn't involved, as it doesn't modify the actual file, it only changes meta data, which AudioLeak ignores.
    But I'd have to say that the process of creating an AAC or any other compressed file shouldn't change level or EQ noticeably at any reasonable bit rate, or the codec wouldn't have passed development testing.  Those things are very obvious.  I'm thinking something else is going on in the process that we don't know about.
    Oh, hang on a sec...just read the thread again. He's transcoding from 320K mp3 > 192K AAC.  I'll have to try that.  I've found that different codecs fight each other sometimes.  
  3. jaddie
    OK, here's the latest.  Started with an AIF, created a 320K mp3.  From that I created a 192K AAC, and a 192K AAC voice-optimized (just in case).  
    Next, I opened them in Audacity and plotted the spectrum of each file (first 238 seconds at least), then layered the plots to see if there were any spectral differences.
    Not even a dB difference anywhere between any files.  No point in showing the plots because they all stack perfectly on top of each other, except of course for the slight loss at the extreme top.  
    Again, all files generated in iTunes.  
    I see no reason for a bass loss.  
  4. Jupiterknight
    Yup, only thing you will see is that the upper frequency cutoff will be lower on the lossy 192K/320K file than on the lossless file. 
    Anyway, this thread and discussion belongs in a different forum.
  5. JamesHuntington
     I just want to save people some time and agree with what i read a lot, that 320 aac is very worth it as an Apple option for portable devices. 256 AAC was not as pleasing to me, no matter what graphs are presented. I learned my lesson the hard way (e.g. 50+ hours of watching my computer convert files.) My way now is cd to lossless to 320 aac because I went to 256 and the sound was noticeably less worthy. I'm sure there's lots of other/better ways but I'm no expert, I just like to rock out and know what my music should sound like. All my songs have been with me for a long time. i only use ipod so I don't have to change and scratch up my cds all the time, because I have ADD lol.
  6. jaddie
    I'm not doubting your observations, it's just that this may be the first time ever somebody's claimed an audible difference between 320 and 256 AAC. According to most published opinion that should have been an inaudible difference. I can't get to testing this right now, but I will later.  
    Did you try playing the same track as 320 and as 256 through an ABX tester?
  7. bigshot
    The difference in bitrates in AAC above 128 isn't an overall sound like sharpness or lack of bass. It's the frequency and severity of random artifacts. At a certain point, the occasional compression artifact disappears and the sound becomes audibly identical to the source. If you'd said that there was a strange digital gurgle in audience applause or a moment where the sound broke up a bit, it might be because the bitrate was too low. But an overall lack of bass indicates one of two things.... Volume level differences and just plain old placebo.
  8. Brooko Contributor
    This ^
    And as you're in sound science - I'd strongly suggest doing a proper abx between aac 256 and aac 320 (use Foobar 2000 & make sure they are level matched  - use replayagain).  I think you'll see those differences disappear.  Personally to me aac 256 is completely transparent - for that matter even aac192 is (for my portable I use vbr at around 200).
    It's actually better knowing your hearing limitations - than not testing and letting placebo limit your options.
  9. bareyb
    The only option I seem to have in iTunes is for 256 kbps (we have music match). I have 3 (hopefully simple) questions if anyone can help.  
    1. Is 256 kbps the best I'm going to get from iTunes or is there a way to download them at a higher resolution? 
    2. Do you guys convert them to a lossless format in iTunes before you sync them to your iPods?
    3. Can you really hear a difference between 256 AAC and Lossless on an iPod (with amp of course)? 
  10. Radioking59
    1.  Yes with no way to get higher
    2.  No, this will only add size to the file and it will sound exactly the same. 
    3.  I don't use AAC or iPod so I'll let someone else handle this. You can find lots of discussion on this with a search. 
  11. bigshot
    In most cases AAC achieves total transparency at 192. If you use 256 VBR, you won't hear an audible difference from that or lossless.
  12. bareyb
    Some of our equipment at work only accepts .wav file format so I have quite a few of those. Is there any point to loading them up on the iPod in .wav format? It sounds like it probably wouldn't make any discernable difference. Would that be correct? Just have to make sure I'm getting the best sound I can.  [​IMG]
  13. JamesHuntington

    1. If you're downloading them from itunes at 256kbps then there's no way to make them better without downloading them again at a higher bit rate. i don't download music a whole lot and am not familiar with itunes size options. Though I have heard downloads as good as a ripped cd when using a good internet connection. Instead of paying to download a higher bit rate of music in order to get better than 256, I'd buy the cd.
    2. When I convert cds on itunes I use lossless option with error correction. Then I convert those lossless to ACC 320 kbps for my iphone and ipod touch.
    3. I hear a difference in many ways, and the biggest difference I hear is between ripped cd to 320 and 256. To me lossless is as good as CD for home use, if done patiently. And 320 is good for rocking on my portable. From lossless to 320kbps i'm saving almost 100mb per album. 256 may be a little more savings of space but I tried it and was very disappointed. 
  14. bigshot
    Most people who do contolled tests fiind that above a certain bitrate, there is no difference between MP3 or AAC and lossless like FLAC,  WAV or the original CD. Most people who believe they can hear a difference haven't taken the time to do a controlled test.
  15. Kiont
    Maybe it is true that we cannot hear certain frequencies, and there is no difference between those formats on what we hear.
    Here is my opinion about it,  when someone plays a guitar, all the range of sound frequencies go into our ears, granted, we won't "hear" all of them, but what if in some way, even though there is no sound, there is still a "feel" of something there, just like when you play a really low or high frequency, there is no sound, but know something is there.
    With MP3 or lossy you are cutting all that "feel" that someone decided you didn't need.
    I don't know, that's my opinion and maybe I'm just crazy, but aren't we all around here?
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