Converting from Constant Bit Rate to VBR?

So I'm starting to doubt the logic behind using CBR for encoding my CD collection. Is there a way to batch convert from CBR to variable bit rate? Or should I re-encode? On average, will it buy me a significant HD space savings if I'm using high bit rate encoding?

Thanks...

Is there a way to batch convert from CBR to variable bit rate? Or should I re-encode?

You should re-encode. Please look at this.

On average, will it buy me a significant HD space savings if I'm using high bit rate encoding?

Yes, That's the point of VBR, to save disk space. I don't know what you would consider "significant" though. You didn't say how your current collection was encoded? Give us that information and we can make estimates from that.

Keep this in mind: It's easier to upgrade the disk drives on the player than it is to re-encode your collection. So if your collection is already at a decent bit rate with a good encoder and not too much high-frequency rolloff, then you might not want to bother.

Tony,

How does 150VBR compare to CBR rates (ie: 150VRB ='s 256CBR)? Is there a comparison somewhere? Sound quality wise that is.

I'm not sure what you mean by 150VBR. Many encoders apply apparently meaningless numbers to their VBR settings. If that's what you're talking about, then there's no way to tell at all. VBR settings are not specified by bitrate, but by how accurate the encoder tries to be. Most encoded at the same VBR setting will approach the same bitrate, but could, conceivably, vary wildly in the face of some (as the Perl guys put it) pathological input. Even knowing what bitrate it tends to average out at isn't going to help because you could encode a 96kbps CBR, which would sound pretty bad, but a VBR file that averaged out at 96kbps could sound pretty good, if there were huge sections of easy-to-compress audio in there, or it could sound equally as bad, if it was fairly consistent.

If you are, instead, referring to 150ABR, then that's a different matter. In that case, the encoder tries to get the average bit rate around the specified number. Unfortunately, there's still no way to tell. It should at least be slightly better than a CBR of the same rate (not there's any such thing as 150kbps CBR), but because of the way most try to deal with averaging (few, if any, do a multi-pass encode), it might not be. It's certainly not going to be a lot better, because the encoders are fairly conservative and don't stray much out of the specified bitrate, because they never know when they might need more bits or have some left over.

Keep in mind that sound quality is:

a) Subjective
b) Hard to determine at bit rates above 128
c) Dependent on the encoder.
d) Dependent on the music being encoded.

Here's what I can tell you: I know that I personally can't tell the difference between a VBR file that averages out to 150kbps, and a CBR file at 256kbps, assuming both were done with good encoders with all the proper quality settings.

With that said, all of my recent rips have been done at 256k CBR because I've got the space on the player and I want to ensure to myself that I never hear any artifacts no matter how slight. My ear stops noticing the artifacts above 160k CBR, so I just do 256 as overkill.

I would do maximum-quality VBR, but I've been using the Rio Central for all my ripping lately and it doesn't do VBR.

I'm encoding at 320kbps CBR. Yes, its maximum overkill but I figured that I'm only going to encode my CD collection once. So now I'm at 70 GIG and wishing I'd upgraded my Empeg using a 60Gig instead of a 40Gig.

Based on the responses, I'll leave it alone. I really do not want to re-encode. Upgrading the drives sounds like a good idea.

Thanks.