Problem concerning 192/160 stereo/JS reencoding, need technical help

[lord_shin]

Ok, quick run down of what my situation is and what problem I'm presenting:

I ripped my entire CD library at CBR 192Kbps joint stereo using MusicMatch 7.5 for the purpose of uploading my music onto my 30gb iPod, a birthday gift. But soon after I started using Soulseek, and, being the addictive program that it is, I've downloaded more albums than I can now fit onto my iPod at 192Kbps. So now I'm going to reencode everything I've got, one album at a time, using Mp3Do's Advanced Mp3 Converter 1.86 (cracked). I want to do 160Kbps joint stereo so I can save about 6 gb of space on my laptop and iPod, but not everything I now have is from the original MM 7.5 encoding. Some mp3s are 192 but only stereo.

Now, what I'm asking is, what difference would reencoding my music, Musicmatch'd or Soulseek'd, make? Do I lose enough sound quality doing such to warrant me to just erase all the music I ripped and re-do them all (200+ CDs) using 160 encoding? Does changing downloaded music at only stereo to joint stereo cause major problems? Should I be using other programs to rip instead of MM 7.5 and other reencoders besides mp3Do's? Are there any other things I should know before I proceed?

For all I know, this is the worst forum to be asking this question, but I gotta ask it SOMEWHERE, and I don't really know any other better place. I figure someone's gotta know out there. If need be, PM me. I'll be keeping tabs on this board, hopefully.

Thanks for any help.

First, lets get the technicalities out of the way. Re-encoding will always result in quality loss. It is always better to re-encode from Source then from an MP3. A 160kbps MP3 encoded from a 129kbs will be of worse quality then a 160kbps MP3 encoded from source. It boils down if the quality loss is acceptable to you or not. Though a mass re-encode maybe be faster and require less work. Re-encode a few tracks and see if the loss is acceptable for you.

Now, about encoder. Music Match Jukebox uses a sub-standard encoder to encode. You are better off using a encoder that use a modern version of LAME. Which appears Mp3Do's does. Though how mach control it gives you is questionable. For ripping and re-encoding we usually recommend CDex. It uses LAME and gives you decent control. For best results with a CBR file use "--alt-preset CBR" from the quality menu then 160 as the bitrate.

As for Stereo and Joint-Stereo, it doesn't really matter. Both can encode into Joint Stereo. Been awhile some I even had to think of this part. Stereo stores each channel independently; Joint Stereo only encodes overlapping samples once from the right and left channels to save space. Either way using either Stereo or Joint Stereo each channel is completely represented so you can go from one to another. (I think)

But, the simplest solution seems to be: Does all the music have to be on the iPod at one time? Can's you just swap some on and off?

[lord_shin]

Well it doesn't have to be, but it's certainly something I'm striving for

I am probably going to test a bit using my iPod as the platform for judgement. Upload one mp3 from one source with a particular encoding, then the same song but a whole different encoding from various places (all labeled of course) then figure out which is best. I might have to use a test mp3, like the THX theme you hear in movie theaters. Thanks for the LAME link, I knew LAME is a good encoder but I don't have a prog that uses it.

Also, is there a difference between CBR and CBR+? I use mp3Trim and it says that a few times, and I don't know what the difference is. And what about VBR to CBR reencodes?

I have never even heard of "CBR+" before. It may be ABR, which is something between CBR and VBR that I never really understood what it was. Built I believe ABR keeps the overall file size the same as a CBR file by only using bits that were freed by other frames. While VBR is free to vary wildly. Therefore ABR may be a better choice.

Any never encoder VBR file will usually be of higher quality then CBR because it is free to adjust the bitrate based on difficulty. If you have some frames in a 192kbps VBR file that are below the CBR target of 160kbps, then that frame will be encode at 160kbps and there will be some loss. Plus harder frames will suffer by being forced into that maximum size of 160 kbps. But encoding from VBR to CBR will still work and be for the most part fine.

For more of the technical crap of MP3 I would check out Hydrogen Audio: http://www.hydrogenaudio.org/

[lord_shin]

Alright, thanks for the help.

[amano]

I wouldn't transcode music (the process of turning a mp3 into an even lower bitrate mp3). if your source mp3s are already done by a substandard mp3encoder, subsequent transcoding wil harm sound quality severely.

and never use cbr, it's very unflexible, so the size/quality ratio is not as good as it could.