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Informed rebuttal of VBR disadvantages appreciated, VBR always rocks, when it comes to lossy compression, right?
Moon
post Oct 16 2008, 09:54
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As already mentinend in this thread some fanboy over at the offical Pioneer forums is making claims that VBR sucks (here and here) in that it needs more processing power compared to CBR and for various other reasons.

I would like to have a well written rebuttal of that statment based on facts so Pioneer might reconsider putting VBR support into their upcoming DJ equipment. I've ripped all my 1000+ CDs to VBR and I wouldn't want to reencode them just because Pioneer doesn't get it right. Thanks!
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Canar
post Oct 16 2008, 18:10
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No, I think I'm going mad. That post I made is quite unclear. Some other guy responded to me with a wall of verbiage that seems to completely miss the point.

Oh boy:
QUOTE
that's plenty of space saving for me, since I can't tell the difference between a WAV and a 320kbps MP3 - but I CAN tell the difference between that and a VBR MP3, or that and a 128kbps MP3.


I'm going to mull this over a bit and respond sometime this evening... what nonsense.

This post has been edited by Canar: Oct 16 2008, 18:16


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uart
post Oct 16 2008, 20:01
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QUOTE (Canar @ Oct 16 2008, 09:10) *
No, I think I'm going mad. That post I made is quite unclear. Some other guy responded to me with a wall of verbiage that seems to completely miss the point.


QUOTE
Basic lesson in computing: ALL instructions and data to be operated upon must exist in RAM. If the instruction or data is external to the RAM, the system must first copy it into RAM (from wherever - Hard Disk, CD, whatever) before it can be used by the CPU. The CPU has no direct access to the hard drive (or, in the case of the CD player, the CD), it must go through the RAM. The CPU also has to actually execute the copying of things into RAM (which in reality is actually handed off to the chipset in the machine, but the chipset won't operate on anything unless it is told to do so by the CPU).

So, as each frame is read to be decoded, it is copied into RAM (quite probably more than one frame at a time, however).

What happens (in an oversimplified manner) is this: the processor that is decoding the frame is dumb. It doesn't know where the frame ends, it just keeps operating on streams of data - possibly operating into some area of the memory that contains something else that isn't MP3 data. This is known as buffer overflow, and can cause crashes and/or bad sounding music playback. This is prevented by setting something called a buffer size - it knows how much data it must read before stopping.

If every frame that is copied into RAM to be operated on is a different size, the CPU needs to be told of this, executing an extra instruction that sets its buffer size. This means that every frame needs at least 2 operations to work - the buffer set, and the buffer read/operate. In a particularly variable MP3, for example, where the frame size is changing A LOT from one to the next, the CPU can't read nearly as much data "ahead" because it never knows where the end will be, and it might read too far before the memory is copied (because a CPU operates many many times faster than the hard drive, or CD, can write data to the RAM) and hit a buffer overflow, causing issues of unknown result. Also, since the CPU is in charge of ALL the RAM and is also doing other things (both in a CD player and in a normal computer), every time it resizes the RAM buffer (because it's copying frames of varying sizes), it might copy something to the area that was occupied by a larger frame but is now free before it needs to use it for audio data again. Now, if it needs to fill that space with audio data (because splitting up a frame in memory would be very bad), it has to MOVE what's there before it can copy new data into that space. This eats up time and processor resources.


Oh yeah I see what you mean Canar. It's so nice of him to give you a basic lesson in computing isn't it tongue.gif.

Really most of what he has posted is just so much rubbish it's ridiculous. Like the suggestion setting a buffer length is a significant part (as in computer load) of decoding an mp3 frame. I'd say he's got no idea of the relative amount of cpu time to do a couple of integer instructions to set up a buffer length compared with even just one part of the mp3 decoding like the DCT for example. I hope there's a developer or two here to read this "basic computing lesson" and make some "constructive critism". Pretty funny stuff really.

This post has been edited by uart: Oct 16 2008, 20:03
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Posts in this topic
- Moon   Informed rebuttal of VBR disadvantages appreciated   Oct 16 2008, 09:54
- - Raiden   Don't waste your energy. Self-absorbed people ...   Oct 16 2008, 10:51
- - halb27   It's all up to whether an encoder works well. ...   Oct 16 2008, 11:27
- - JensRex   Yes, don't waste your time. That guy is comple...   Oct 16 2008, 11:43
- - Slipstreem   As the other guys have already said, you're wa...   Oct 16 2008, 12:56
|- - add   QUOTE (Slipstreem @ Oct 16 2008, 13:56) C...   Oct 16 2008, 16:40
|- - Lyx   QUOTE (add @ Oct 16 2008, 17:40) QUOTE (S...   Oct 16 2008, 17:19
- - probedb   No point with some of these people....I've giv...   Oct 16 2008, 12:59
- - Canar   These threads are really old. I created an account...   Oct 16 2008, 16:59
|- - Synthetic Soul   QUOTE (Canar @ Oct 16 2008, 16:59) I resp...   Oct 16 2008, 17:08
- - Canar   No, I think I'm going mad. That post I made is...   Oct 16 2008, 18:10
|- - uart   QUOTE (Canar @ Oct 16 2008, 09:10) No, I ...   Oct 16 2008, 20:01
- - Slipstreem   Well, we have an answer of sorts over there from a...   Oct 16 2008, 18:18
- - Soap   Mind, if you do decide to argue: The argument that...   Oct 16 2008, 18:59
- - Slipstreem   I'm specifically not joining that forum as I...   Oct 16 2008, 19:39
- - Canar   Who is BDX?   Oct 16 2008, 20:03
|- - DJRyanJ   Alright guys, I'm the guy who did the wall of ...   Oct 16 2008, 20:49
|- - halb27   QUOTE (DJRyanJ @ Oct 16 2008, 21:49) ...S...   Oct 16 2008, 21:29
|- - kwanbis   QUOTE (DJRyanJ @ Oct 16 2008, 19:49) 5) W...   Oct 16 2008, 21:36
- - uart   I dont know, it's not me. Does anyone have a t...   Oct 16 2008, 20:06
- - Slipstreem   It wasn't me either, and I don't have a tr...   Oct 16 2008, 20:12
- - kornchild2002   I will post just to be ballsy. I don't see Pu...   Oct 16 2008, 20:48
- - Canar   I don't have the time right now to get more in...   Oct 16 2008, 21:13
- - m0rbidini   Pioneer should support VBR and stfu. If using VBR ...   Oct 16 2008, 21:57
- - DJRyanJ   OK, I have a brief moment here before my midterm s...   Oct 16 2008, 22:00
|- - Ron Jones   QUOTE (DJRyanJ @ Oct 16 2008, 14:00) Why ...   Oct 16 2008, 22:59
|- - m0rbidini   QUOTE (DJRyanJ @ Oct 16 2008, 22:00) QUOT...   Oct 16 2008, 23:32
|- - kwanbis   QUOTE (DJRyanJ @ Oct 16 2008, 21:00) I...   Oct 17 2008, 03:09
- - [JAZ]   I guess most it said already but I'd like to c...   Oct 16 2008, 23:01
- - Axon   What MP3 decoding library does Wavelab use? It...   Oct 16 2008, 23:02
- - DJRyanJ   QUOTE About 0.01% had issues. Most where CBRs. Di...   Oct 17 2008, 04:39
|- - kwanbis   QUOTE (DJRyanJ @ Oct 17 2008, 03:39) Did ...   Oct 17 2008, 05:06
- - xmixahlx   1. regarding the difficulty of decoding VBR it...   Oct 17 2008, 05:52
- - m0rbidini   QUOTE I've seen this in my very limited video ...   Oct 17 2008, 11:00
- - Lyx   Why have a long discussion when it all can be summ...   Oct 17 2008, 13:21
|- - halb27   QUOTE (Lyx @ Oct 17 2008, 14:21) Why have...   Oct 17 2008, 14:33
|- - lvqcl   QUOTE (halb27 @ Oct 17 2008, 17:33) QUOTE...   Oct 17 2008, 14:49
|- - Lyx   QUOTE But maximum bitrate for LAME VBR (i.e. lame ...   Oct 17 2008, 15:13
- - pdq   I am guessing (and I don't really know anythin...   Oct 17 2008, 13:50
- - Slipstreem   Won't the part of the audio stream being worke...   Oct 17 2008, 13:57
|- - pdq   QUOTE (Slipstreem @ Oct 17 2008, 08:57) W...   Oct 17 2008, 14:48
- - Synthetic Soul   DJRyanJ, kudos for making the effort to partake in...   Oct 17 2008, 14:04
- - Slipstreem   I'm gonna have to go and read more about how t...   Oct 17 2008, 15:01
- - Slipstreem   The only problem I can see with that is that some ...   Oct 17 2008, 15:43
|- - Lyx   QUOTE (Slipstreem @ Oct 17 2008, 16:43) T...   Oct 17 2008, 15:56
- - halb27   IMO the old --preset scheme or a similar one addre...   Oct 17 2008, 15:59
- - greynol   Now we're just going around in circles. There...   Oct 17 2008, 16:05
|- - Lyx   QUOTE (greynol @ Oct 17 2008, 17:05) Now ...   Oct 17 2008, 16:21
- - Synthetic Soul   We're also going way off-topic...   Oct 17 2008, 16:53
- - Slipstreem   A quick heads-up (not that I've been spying). ...   Oct 17 2008, 19:25
- - DJRyanJ   I actually know Pulse personally and he's not ...   Oct 17 2008, 20:59
|- - kornchild2002   QUOTE (DJRyanJ @ Oct 17 2008, 13:59) I...   Oct 17 2008, 21:21
|- - Canar   QUOTE (kornchild2002 @ Oct 17 2008, 13:21...   Oct 17 2008, 21:48
||- - kornchild2002   QUOTE (DJRyanJ @ Oct 17 2008, 14:40) Gene...   Oct 17 2008, 22:27
|- - kwanbis   QUOTE (kornchild2002 @ Oct 17 2008, 20:21...   Oct 19 2008, 19:25
- - Neasden   On the switch subject, I just would like to add th...   Oct 17 2008, 21:34
- - DJRyanJ   QUOTE (kornchild2002 @ Oct 17 2008, 13:21...   Oct 17 2008, 21:40
|- - Slipstreem   QUOTE (DJRyanJ @ Oct 17 2008, 21:40) What...   Oct 17 2008, 21:59
- - DJRyanJ   QUOTE (Slipstreem @ Oct 17 2008, 13:59) O...   Oct 18 2008, 01:11
|- - Synthetic Soul   QUOTE (DJRyanJ @ Oct 18 2008, 01:11) I...   Oct 18 2008, 10:00
- - Moon   Well, I'm sorry but after finding out about Pi...   Oct 18 2008, 11:11
|- - Synthetic Soul   QUOTE (Moon @ Oct 18 2008, 11:11) Well, I...   Oct 18 2008, 19:04
- - Slipstreem   With reference to your last paragraph, have you tr...   Oct 18 2008, 13:04
- - Moon   I'm gonna try em tonight. I've also conver...   Oct 18 2008, 16:36
- - pdq   If even a single frame uses 320 kbps then the enti...   Oct 18 2008, 22:16
- - Moon   QUOTE (Synthetic Soul @ Oct 18 2008, 20:0...   Oct 19 2008, 09:24
- - DJRyanJ   QUOTE (Moon @ Oct 18 2008, 03:11) a) a fu...   Oct 19 2008, 10:33
|- - Synthetic Soul   QUOTE (DJRyanJ @ Oct 19 2008, 10:33) I su...   Oct 19 2008, 11:54
|- - Moon   QUOTE (DJRyanJ @ Oct 19 2008, 11:33) QUOT...   Oct 20 2008, 09:50
- - shadowking   Dj's of the world please stop bothering us wit...   Oct 20 2008, 12:50
- - DJRyanJ   I'm trying to do some comparisons, and I'm...   Oct 21 2008, 19:58
|- - Canar   http://ff123.net/samples.html is a good place to s...   Oct 21 2008, 20:16
- - halb27   On problemSamples folder you'll find those sam...   Oct 21 2008, 20:25
- - DJRyanJ   QUOTE (Canar @ Oct 21 2008, 13:16) Howeve...   Oct 21 2008, 20:58
|- - halb27   QUOTE (DJRyanJ @ Oct 21 2008, 21:58) .. f...   Oct 21 2008, 22:06
|- - Moon   QUOTE (DJRyanJ @ Oct 21 2008, 21:58) I...   Oct 21 2008, 22:28
|- - Slipstreem   QUOTE (DJRyanJ @ Oct 21 2008, 20:58) I...   Oct 22 2008, 00:52
- - lvqcl   QUOTE It refers to the LAME problem samples page f...   Oct 21 2008, 21:09
|- - Canar   QUOTE (lvqcl @ Oct 21 2008, 13:09) http:/...   Oct 21 2008, 21:26
- - DJRyanJ   That's the plan, slipstreem. Moon, I'll s...   Oct 22 2008, 04:31


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