Need an audiophile...this one's a doozy!

College Confidential Community
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<p>Ok, this is a puzzling question, but for those sharp enough, bear with me.</p>

<p>AAC carries greater quality than mp3 with the same bitrate and size.</p>

<p>So if you have 320kbps mp3, and you convert it to 256kpbs AAC, it's essentially the same quality.</p>

<p>However, once a file is AAC, you seemingly lose this benefit when you convert it to a lower-bitrate AAC, right?</p>

<p>To make it clearer, I'll describe my particular situation:</p>

<p>Throughout the past year or so, I've been converting mp3s into AACs of equal or slightly less bitrate, so as to not lose any quality. In other words, If I had a 237kbps mp3, I'd convert it to a 224kbps AAC. If I had a 192kbps mp3, I'd convert it to a 192kbps AAC.</p>

<p>However, now I'm thinking all I really need are 128kbps AACs. BUT, my entire music library is already in AAC, not mp3. So, I'd be converting from 160+kbps AAC down to 128kbps AAC.</p>

<p>My question, then, is that if I'm already STARTING with, say, a 192kbps AAC, and I convert it to a 128kbps AAC, will this 128kbps AAC still have the same quality as a 192kbps mp3, which is what it would have had if it had been converted from an mp3?</p>

<p>I realize this problem is rather hard to grasp, but if you understand what I'm saying, PLEASE help. :)</p>

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<p>Although I regularly convert between mp3 and AAC, I don't typically mess with bitrate too much, so take anything I say with a grain of salt.</p>

<p>From my understanding, it seems only logical that converting a file of the same type to a lower bitrate would result in lesser quality sound.</p>

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<p>Yes, definitely. But how steep would that downgrade in quality be?</p>

<p>I guess the fundamental, implied question I'm asking is:</p>

<p>If I converted all my mp3s into equivalent or slightly less AACs, and then converted all those AACs into 128kbps AACs, would those last files be of lesser quality than had I just converted all my mp3s directly into 128kbps AACs?</p>

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<p>Ummm, converting between mp3 and AAC can give you a lower quality file depending no matter what the bitrate, depending on what encoder you use. If you use an encoder that takes the information, gives you raw PCM output, then converts the PCM to AAC, it can diminish the quality since the frequencies cut out by AAC and mp3 (and even WITHIN the mp3 encoder spectrum the frequencies taken out change according to what encoder you use) differ.</p>

<p>The way the mp3 converter works is: you take PCM data, which is nothing more than amplitude data on the time-spectrum, break it into frames (26 ms), and you perform a Fourier transform on them. This will give you data on a frequency domain. You take those frequencies, and you can cut out inaudible signals. Then, you can find a fourier coefficient that you will reuse in a summation formula to get a new signal that is ALMOST identical to the original, but with some of the smaller and larger frequencies cut out since we cannot hear them anyway. To learn more about that, just look up harmonics and signals as well as Fourier analysis on google sometime. Anyway, with the new signals, you can now place them in a frame, and your DEcoder will reconstruct the signal at each frame. The higher the bitrate, the more sum of sinusoidals that can be produced. Hopefully you understand this somewhat and you can see why converting between LOSSY codecs can cause diminished quality no matter what the bitrate. </p>

<p>
[quote]
So if you have 320kbps mp3, and you convert it to 256kpbs AAC, it's essentially the same quality.

[/quote]
</p>

<p>Again, this is not so, unless you're using the SAME RAW source. If you're converting between lossy codecs(mp3, mp4,mpg,aac, and codecs that provide a raw data to compressed data ratio of ~10:1, usually) even between the same codec at the same bitrate, you will lose fidelity. If you're converting between LOSSLESS codecs (wav/pcm, occ[I think], ones that don't provide such a great compression ratio). So, in my opinion, if you don't want to lose a great amount of quality, DON'T convert b/w mp3 and acc unless you do it once at most (and, even then, it can start to sound a little ick).</p>

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<p>Well, crap. That's not good news. =/</p>

<p>So basically, I'm stuck with a bunch of unnecessarily-high-bitrate lossies. >_<</p>

<p>How noticeable is the reduction in quality? I mean, in all honesty, my 128kbps aac's (converted from mp3's) sound pretty damn good to me. Of course, this may just be because my equipment is too cheap to let the higher quality of non-lossy and non-low-bitrate tracks shine through. Indeed, the whole reason why I kept high bitrates was for the future, when I can afford better musical equipment. But I don't know if I'll actually be able to tell the difference. o.O</p>

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<p>What's the problem if it sounds good to you? Just convert. You'll lose a few bits of data but anything around 192 kbps is fine.</p>

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<p>192kbps mp3, or aac? My intent is to convert everything to 128kbs aac. The problem is what I'm already starting out with extremely-compressed lossies to begin with.</p>

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<p>If it were me, I'd just keep them the way they are.</p>

<p>
[quote]
What's the problem if it sounds good to you? Just convert. You'll lose a few bits of data but anything around 192 kbps is fine.

[/quote]

No, you don't just "lose a few bits of data." When using lossy codecs, you deal with fourier analysis that can cause phase shifts, jitter, fractioned/amplified amplitude data, certain noise effects, etc.</p>

<p>Now, you if you want to take some music around with you on your iPod or something, and it sounds fine TO YOU, there's no problem converting. However, if you're a DJ or something, it seems best to keep your data the way it is.</p>

<p>What's up anyway? Are you lacking in space? Storage is cheap these days, so that shouldn't be an issue.</p>

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<p>This thread makes me feel stupid.</p>

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<p>^</p>

<p>I'm not a DJ, but I do take my music pretty seriously. I've got over 82 days' worth of music, and a little over one-third of that is currently non-128kbs AAC, so choosing whether or not to convert is a pretty big investment.</p>

<p>Space is actually the only problem. I'm disinclined to pay $80 for a greater-capacity hard drive when I've already got a 184-gig hard drive that kind of puts a healthy "limit" on how much music I get. Also, it'd have to be an internal rather than external (for portability's sake), and it'd seem like a waste to stop using a perfectly-fine-but-just-a-few-gigs-too-small hard drive.</p>

<p>Anyways, I suppose the main crux of the problem is whether or not I can actually distinguish between the source and a 128kbps AAC version of it. I've tried several listening tests, and I honestly couldn't, BUT that might just be my equipment.</p>

<p>So, do you think that this laptop:</p>

<p>Amazon.com:</a> Toshiba Satellite A205-S4777 15.4-inch Laptop (Intel Core 2 Duo Processor T5450, 2 GB RAM, 200 GB Hard Drive, Vista Premium): Electronics</p>

<p>...and these headphones:</p>

<p>Amazon.com:</a> Sennheiser EH-150 Evolution Hi-Fi Stereo Headphones: Electronics</p>

<p>...would allow a listener to adequately hear the full implications of high-quality audio? If not, then I guess I'll just have to wait until I can try a listening test with better equipment, but if so, then really I feel like these extra kbps are just wasting disk space.</p>

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<p>Well, after about a minute's worth of intense critical thinking, I decided converting a 192kbps AAC (at about 224kbps mp3 quality) to a 128kbps AAC would probably result in 160-192kbps mp3 quality. Does anyone want to lend their feedback on whether or not they think this assessment is true?</p>

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<p>It's probably already been made clear, but converting between any 2 lossy codecs always results in a loss of quality, even if it's from a lower bitrate to a higher bitrate. If you convert the 192 AAC to 128 AAC, it will sound much worse than if you were to rip a CD directly into 128 AAC. If you have something lossy, don't convert it - listen to it as it is, re-rip it from the CD, or get a lossless (FLAC, WAV, ALAC) version and convert that. </p>

<p>For the record, by far the best sounding lossy codec is v0 MP3(vbr) - I have never been able to distinguish between it and 320kbbs, or even lossless(I'm not exactly an audiophile though, I'm only listening on decent headphones through my computer's soundcard which isn't anything special). If v0 takes up too much space, V2 is solid as well. IMO both of those sound better than 192kbbs AAC. </p>

<p>v0, v2 etc are all LAME codecs btw, google LAME for more info</p>

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<p>Well, I've already converted all my music into AAC, so converting from the source is pretty much out of the question.</p>

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<p>Aside from the time involved, why is converting from the source CD's out of the question?</p>

<p>BTW, you could get a 1 TB usb hard drive at Buy.com now for $99.
SimpleTech</a> SimpleDrive 1TB USB 2.0 External Hard Drive - Buy.com</p>

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<p>^ Every single one of my 25,000+ tracks is manually labeled, so there's no way I could re-label all those. Especially the classical music - that would take ages.</p>

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<p>How old is that hard drive? You realize those things tend to fail every few years? With what sounds like a priceless collection is the money for a small drive really so much? You can get a ~300 GB external for like 60$.</p>

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<p>
[quote]

For the record, by far the best sounding lossy codec is v0 MP3(vbr) - I have never been able to distinguish between it and 320kbbs, or even lossless(I'm not exactly an audiophile though, I'm only listening on decent headphones through my computer's soundcard which isn't anything special). If v0 takes up too much space, V2 is solid as well. IMO both of those sound better than 192kbbs AAC.

[/quote]
</p>

<p>I find the same to be true. That's because it can adjust every 26 ms how much data is needed to recreate a signal, and some signals require less information to be recreated while others need a little more.</p>

<p>And, yawn, that equipment should be fine. You just might not have hearing sensative to certain frequencies (yours may even stop at 16kHz). Mine is better than average, ranging from 20 kHz (lowest that can be heard by human ear) to a high of ~20 kHz (which even for my young age is high).</p>

<p>This will tell you more about it:
Psychoacoustics</a> - Wikipedia, the free encyclopedia</p>

<p>And here's a chart demonstrating it graphically:
<a href="http://wiki.hydrogenaudio.org/images/8/82/ATH.png%5B/url%5D"&gt;http://wiki.hydrogenaudio.org/images/8/82/ATH.png&lt;/a&gt;&lt;/p>

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<p>I have to agree with what has already been said. Lossy to lossy just results in lower quality. At the very least, rip/copy from a lossless source, or get highest quality lossy and only convert once, at most, to avoid more degradation.</p>

<p>I also have to stress that getting a new hard drive is a good investment considering the work you put in to the collection you have.</p>

<p>Browse through Newegg or TigerDirect. You can't go wrong there. You can easily find a solid Western Digital 500GB internal HDD for less than $70. Other than that, just burn copies onto Taiyo Yuden discs as data files.</p>

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<p>
[quote]
Mine is better than average, ranging from 20 kHz (lowest that can be heard by human ear)

[/quote]
</p>

<p>Oops, I meant to say 20 Hz, not kHz.</p>