Converting 192 AAC to 160

Discussion in 'iPod' started by Rantipole, Aug 5, 2005.

  1. macrumors 6502

    Rantipole

    Joined:
    May 24, 2004
    Location:
    Boston
    #1
    I have ripped all of my albums to 192 AAC. I am beginning to question if this was overkill for my purposes. (When I want best quality, I listen to the original on my stereo. I use the AAC files for iPod, computer speakers, and the occasional "party mix" that I throw on boomboxes at other peoples houses).

    Anyway, if I were to reduce the file size to 160, to help out my iPod battery, would I lose any quality BEYOND that which I would have lost in the first place? I mean, will they sound the same as if I ripped the CD to 160 in the first place? Or, since I am starting from a AAC file, even at a higher bit rate, will the compression come out worse? Am I making sense?

    Because, I'm not re-ripping everything! But, if the compression from 192 to 160 results in the same sound quality as a "freshly ripped" 160 file, I might go ahead and do that.

    Thanks.
     
  2. macrumors 604

    Lacero

    Joined:
    Jan 20, 2005
    #2
    Regardless of what self-described "audiophiles" tell you, anything over 128Kbps AAC is overkill.

    mp3 Tests
     
  3. macrumors 68020

    dubbz

    Joined:
    Sep 3, 2003
    Location:
    Alta, Norway
    #3
    Lacero: If you say so. Can't say I agree with this guy... (and I'm no self-proclaimed "audiophile").

    I'd suggest you do an ABX (audio blindtest) to get some clue on how low you can go before hearing a difference. Not all of your tracks, just a few different ones. Despite that I don't agree with the linked article, I'd agree that 128kbps is fine for portable listening in most cases. Background noise and the like will mask out some of the negative results of a low birate.

    As for going from 192 to 160.. There's a theoretical difference, but I doubt you'd notice it.

    Of course, all of this depends on your own ears and equipment, so you should really test it on your own. We all got different levels of hearing, and some are better able to detect differences (good or bad).
     
  4. macrumors 6502

    Joined:
    Mar 3, 2005
    Location:
    Virginia, U.S.A.
    #4
    There would likely only be some compression noticeable if you were going from 192AAC to 128AAC; and even then, it would only be audible in rare instances. A 160AAC is great insurance for tracks that require the best clarity possible, particularly involving the reproduction of proper acoustic resonances in jazz or orchestral works.
     
  5. macrumors 6502a

    Joined:
    Jul 17, 2002
    #5
    Back to the original question... compressing a higher bitrate aac to a lower bitrate aac is absolutely not the same as ripping a song from CD to aac. Don't do it!
     
  6. macrumors 601

    HiRez

    Joined:
    Jan 6, 2004
    Location:
    Western US
    #6
    No, you will lose quality when recompressing an already compressed file. I strongly recommend you do not do this! IMHO it's not worth the minor space savings you will achieve. Reripping at 160, fine. Maybe recompressing from 320 to 160, fine. But I would never convert 192 -> 160. It comes down to your ears and your equipment. If you insist, maybe do a test on a few songs to see if you notice the difference.
     
  7. Moderator emeritus

    WinterMute

    Joined:
    Jan 19, 2003
    Location:
    London, England
    #7
    Those of us who make a living in audio will probably disagree with you Lacero, I certainly do, I'm no audiophile, I'm an audio professional, there's a difference and we base our listening on different criteria.

    There is a clear and unmistakable difference between uncompressed PCM audio (wav or aiff) and ANY lossy codec, even 320Kbps AAC (my personal favourite) provided you are listening via a system that is capable of reproducing audio accurately.

    Personally I can hear the difference between 16 and 24-bit audio, 44.1Khz, 96Khz and 192Khz recordings, and even those recorded on different systems (RADAR is perhaps the best, followed by Protools HD, although 2" analog 24-track is by far the most musical).

    Back on topic, transcoding an already lossy codec will cause artifacts, I suggest you re-rip your CD's to 160 rather than down-sampling them.
     
  8. thread starter macrumors 6502

    Rantipole

    Joined:
    May 24, 2004
    Location:
    Boston
    #8
    Thanks to those who answered my question. I suspected as much (double compression=bad), but wasn't sure. Re-ripping? Probably won't do at this point. Probably just rip new stuff at 160. I'll do a blind taste test anyway, as there is a song that I think would be perfect for this, for the geeky fun of it.

    Regarding that article, it actually does NOT say that there is no audible difference between 128 and higher bit-rates. Meh, I was going to say more, but that's a whole other argument covered in many other places.
     
  9. macrumors regular

    Ti_Poussin

    Joined:
    May 6, 2005
    #9
    The best way is to test it on few files and see if you like it or not, you may want to use mAC3dec application to batch convert all the file quickly.
     
  10. macrumors 603

    rainman::|:|

    Joined:
    Feb 2, 2002
    Location:
    iowa
    #10
    Well another vote against Lacero's position, it depends on your criteria, i'm no audiophile but 160aac is the lowest I'll rip in. ANYWAY, as was said, you must re-rip, there's no way (yet, there will be smart downcoders before long) to encode as if it was off the disc, it'd be too lossy. Sorry.
     
  11. macrumors regular

    Joined:
    Jul 2, 2003
    #11
    I never recommend trying to rip at lower rates. Storage has never been cheaper. All my music is at 160k on mp3. The next time I am going to rip is as WAV, when we have a 350GB iPod. Laugh as you may. 5 Years ago we thought 60 GB was unbelievable.
     
  12. Moderator emeritus

    mkrishnan

    Joined:
    Jan 9, 2004
    Location:
    Grand Rapids, MI, USA
    #12
    The basic reason is called aliasing. Think about if you draw a half circle, on a sheet of paper, and then make dots at every 30 degrees along the half circle (so there are seven dots on it). Then connect the seven dots together with straight lines. The connect-the-dot lines match the circle fairly well, right, although not perfectly? Now, on the same circle, make dots every 45 degrees apart. First, connect them together with straight lines, like you did before. Then, go in from each dot to the nearest place on the straight lines from the 30 degree dots, and make dots there and connect those together. It's hard to visualize, but if you actually follow the steps and do it, you should see that the set of 45 degree dots on the circle, connected together, make a much better circle than the set of 45 degree dots, transposed onto the 30 degree lines, and then connected together. That's what happens when you resample.
     
  13. thread starter macrumors 6502

    Rantipole

    Joined:
    May 24, 2004
    Location:
    Boston
    #13
    Yeah, but I'm thinking more about battery life.
     
  14. Moderator emeritus

    WinterMute

    Joined:
    Jan 19, 2003
    Location:
    London, England
    #14
    I run a mixture of 320Kbps AAC and Apple Lossless on my 60Gb iPod, and I get about 8 hours off one charge, although I notice the drive spinning up more often if it hits a run of lossless tracks.

    It's a trade-off, but the audio quality is important to me.
     
  15. macrumors 68020

    Joined:
    Mar 30, 2004
    #15
    Very cool, thanks for that. :)
     

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