Apple's Bit Rate Conversion

[omahapianist]

Hello Everyone,

 

I just recently joined this CA site as I discovered it quite by accident. I had no idea something like this existed and being an audiophile for most of my life with a recent interest in PC-based music over the past couple of years, I thought I could learn a lot here. I do not have an outboard DAC at this time so I'm spending time reading all I can about them and what would be best for me. Fascinating stuff! Currently, I have a laptop PC running Vista with a so-called "high-def" upgrade to a Realtek soundcard, AudioQuest copperhead mini-to-RCA cable connected to a Channel Island Audio VHP-1 headphone amp which powers my Grado SR-325 headphones which is re-cabled with Moon Audio's Blue Dragon headphone cable complete with a Cardas 1/4" plug.

 

My question (or confusion) concerns Apple's bit rate conversion process. I use both Zune (I also have a Zune 80) and iTunes software for my music which are loaded with WMA and Apple lossless file respectively. I also have a fair number of lossy files as well. My iTunes software is set to convert audio files, CD's or otherwise, to their Lossless format. What I don't understand is how Apple "converts" an MP3 file (mostly 320 kbps for my lossy files) to Apple Lossless since an MP3 is essentially truncated. Is there some trick that Apple does to actually create a lossless file (which I can't imagine) or is this some kind of illusion? I have a subscription to emusic and their files are encoded in an MP3 format ranging from 192 to 320 kbps. I have dragged a number of these files to iTunes because I want to eventually get rid of Zune and, of course, it tells me that it can convert them to Apple Lossless. Any thoughts or comments would be appreciated. Thanks.

 

And thanks for a great site, Chris!

 

Randall Collins

 

[The Computer Audiophile]

Hi Randall - Welcome to Computer Audiophile. I'm glad you found the site. I'm pretty sure you can get your questions answered around here as long as you ask!

 

Converting lossy MP3 to Apple Lossless does nothing but increase the size of the file unfortunately.

 

[omahapianist]

...but now I'm wondering since converting MP3 to Apple Lossless (or AIFF, WAV, etc,) is, technically, a "bit-for-bit" transfer of the original source, it should sound "better" with a good DAC unit. I might be completely whack-o for thinking this but I guess one has to be like this to post such a question. :-P

 

[The Computer Audiophile]

"...since converting MP3 to Apple Lossless (or AIFF, WAV, etc,) is, technically, a "bit-for-bit" transfer of the original source..."

 

There is no such thing as an MP3 bit for bit copy of the original source. MP3 throws out data to make the file smaller. This data cannot be recovered by converting to Apple Lossless or any other format.

 

[omahapianist]

...however, I'm trying to figure out the reason why iTunes offers a conversion from MP3 to Lossless. Perhaps the best way of looking at it is to imagine an 8 oz. glass with 8 oz. of water (WAV). Then pour, say, 4 oz. of water out of it (MP3) and pour the remaining 4 oz. into a 12 oz. glass (MP3 to Lossless). There's no sound difference (or taste difference in my example) so there must be some reason other than taking up more space as to why iTunes, and different softwares, do this.

 

I'm also curious how a DAC would read a file like this since it states that it's a 44.1 kHz file but it really isn't.

 

Great, now my brain hurts! :-P

 

:-)

 

[Codifus]

Randall,

 

here are a few things to keep in mind;

 

1. Ideally, you really should only convert to a lossy format once, and that conversion should originate from a lossless file. Going from MP3 to AAC compounds the lossiness and you wind up with a much much less true-to-the-original audio file.

 

2. Itunes, at least with version 7, has a merely adequate MP3 encoder. Apple probably figured that they have AAC, which is a better lossy format, so why bother?

 

3. Lastly, converting a lossy file to lossless only creates a lossless version of that original lossy file. In other words, there's no improvement at all and the file size gets unnecessarily huge. This type of conversion should really never happen.

 

CD

 

[BobH]

...however, I'm trying to figure out the reason why iTunes offers a conversion from MP3 to Lossless.

 

Probably for the same reason McDonald's offer a salad - it needs to be there for those that need it to be there, except nobody who uses McDonald's really needs it to be there. If you see what I mean.....

 

The answer to the other bit of your headache, is that the dac will see a reconstituted audio stream. This is the job of the playback software. If an MP3 was originally made from a 16/44.1 file. then the dac will get a 16/44.1 audio stream - the stuff that got chucked away will be replaced with whatever the codec decides to chuck back in. Not all codec's are created equal and some will do a better job than others, but what you get out is a 'best guess' 16/44.1 audio stream. This is what the dac gets.

 

In the case of a lossless file, this is initially created in such a way that it can then be reliably re-created, by the playback software, to be exactly the same as the original file. Nothing gets chucked away, it just gets re-written in a way that saves hard disc space.

 

So your analogy is correct - there is no point to converting mp3 to lossless. The facility is there because it's there, not because it's useful!

 

[omahapianist]

Thanks. That makes perfect sense to me now. Now I hope emusic will one day offer hi-res downloads instead of MP3's because there's a lot of really great music there. In the meantime, I'm going to focus more on researching DAC units and hi-res music sites.