iPod Encoding AACs into Lower Bit-Rate AACs?

[lorkp]

Will a 320 AAC converted into a 128 AAC be as good as a 128 AAC encoded directly from the CD?

 

[Lacero]

No, but I doubt you'll hear the difference.

 

[balamw]

No, but I doubt you'll hear the difference.

I agree with Lacero, but just wanted to point out that I read an article about this recently, I just can't remember where, that seemed to conclude that you were better off transcoding, i.e. going from 320 kbps MP3 to 128 kbps AAC and vice versa, as fewer compression artifacts were being introduced.

I'll try to find the article, I think it was at hydrogenaudio.

B

 

[WinterMute]

I agree with Lacero, but just wanted to point out that I read an article about this recently, I just can't remember where, that seemed to conclude that you were better off transcoding, i.e. going from 320 kbps MP3 to 128 kbps AAC and vice versa, as fewer compression artifacts were being introduced.

I'll try to find the article, I think it was at hydrogenaudio.

B

That isn't the question the OP asked, but the conclusion is correct.

If you code to 320 then downsample (transcoding is actually moving from one codec to another), then you are introducing artifacts on your artifacts, coding from a CD will yield better results, but as Lacero notes, you'll need good ears and a good system to hear those results.

 

[jdechko]

But also remember that if you decide to re-encode them again you will introduce more artifacts because of the compression algorithm. Also, there are, as was said earlier, artifacts from transcoding as well. For instance, (free, really) mp3's that I downloaded from the internet at 160 were transcoded into 128 AAC and there is definitely some popping and clicking noises that werent there... same with Lossless (didnt play in iPod, ) to AIFF (skipped in iPod ) to 320 AAC.

So you should be fine as long as you dont re-encode or transcode more that once. If you decide that you want something other than 128 after re-encoding, I'd suggest re-ripping the CD.

 

[seamuskrat]

What is the best method to transcode AAC to lower bitrate using iTunes? Or is it best to use another application?
I have a number of audiobooks that could save some serious space being transcoded to a lower bitrate without much fear of loss of quality. Other than re-ripping - way too much time required, I need a quick solution to transcode so I can fit my books on my Nano.

 

[balamw]

you'll need good ears and a good system to hear those results.

Of course for those with good ears and good systems 128 kbps, regardless of how it was encoded, is usually not good enough.

Clarifying the point I was trying to make. For "best" results, definitely go back to the CD or other lossless source (FLAC, Apple Lossless) and encode directly to 128 kpbs AAC. For "better" results, the OP might want to consider using 320 kps MP3 instead of 320 kbps AAC as the high bitrate source for transcoding to 128 kbps AAC. This would minimize compression artifacts. Most people, including myself, however probably would not be able to tell the difference and would get "good" results from transcoding from 320 kbps AAC to 128 kbps AAC.

What is the best method to transcode AAC to lower bitrate using iTunes?

I've used both Nero on Windows and iTunes to downsample audiobooks, and Nero provides far more options in the encoder, including VBR and lower bitrates. However, iTunes 6 has the new podcast setting, which optimizes for voice, and the files are guaranteed iPod compatible. You might also want to consider going low bitrate VBR on LAME now that MP3s can be flagged bookmarkable.

B