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Topic: Just Curious (Read 3343 times) previous topic - next topic
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Just Curious

There are 128, 160, 192, 224, 256, 320 Kbps in vbr encoding,
But why there is no 288 Kbps?
Because at such a high bitrates, there is no many advantage to have 288 between 256 and 320 Kbps?
All Rights Reserved All Wrongs Reversed.

Just Curious

Reply #1 –
Because MP3 Frame sizes are fixed to these values. Musepack or Vorbis use arbitrary frame sizes.
"To understand me, you'll have to swallow a world." Or maybe your words.

Just Curious

Reply #2 –
Quote
There are 128, 160, 192, 224, 256, 320 Kbps in vbr encoding,
But why there is no 288 Kbps?
Because at such a high bitrates, there is no many advantage to have 288 between 256 and 320 Kbps?
[a href="index.php?act=findpost&pid=244817"][{POST_SNAPBACK}][/a]


The bitrate is identified by a 4 bit value in the frame header which lies in the range 0-15. 0=free format, 15=invalid/forbidden (Probably chosen to avoid false synchronization). So, there are 14 4-bit-combinations left to tell us what bitrate has been used.  The layer 3 bitrates follow some kind of exponential law:
Code: [Select]
   32  40  48  56    | step = 8
   64  80  96 112    | step = 16
  128 160 192 224    | step = 32
  256 320            | step = 64


Note: If the LAME encoder (in VBR mode) thinks a 288 kbps frame would be a cool thing then it just makes use of a 320 kbps frame and leaves some free space in the bit reservoir for the next frame. So, in combination with the bit reservoir it really does not matter if there's a 288 kbps mode or not. (The space isn't wasted)

HTH,
Sebastian

edit: copy-&-paste bug fixed

Just Curious

Reply #3 –
SebastianG

your table is wrong, 128kbps is in the +16kbps range that's why 128kbps will never be considered "high bitrate",  anything above 128kbps is wrong
(128+16=144 ... not 160kbps)

see
http://www.hydrogenaudio.org/forums/index....showtopic=27706
for a correct table

Just Curious

Reply #4 –
xmixahlx

The specific reason is that at this high bitrate the multiple is +64kps not +32kbps

160-192-224-256==>32kbps Step
320==> orpheline bitrate in the 64kbps step range

That is the reason why I dislike 320Kbps so much, for me CBR 320kbps should not be available in lossy codecs, 320kbps is only clever as a frame bitrate for VBR & only when really needed ... always using it (CBR) completly kill the purpose of lossy compression ... if you are paranoid & want perfect backup use lossless not lossy CBR 320 ...

288kbps is not used because it's a multiple of +16kbps in the +32kbps multiple range but indeed it would be sometime better than 320kbps in term of quality-size ratio but you can apply that for any frame multiple of 8kbps ... that's one of the advantage of Vorbis-AAC & one  of the reason why these codecs achieve better quality at lower size ....

again read my post about generic quality setting for lossy codecs-bitrates all this will get clearer in your mind ...

Just Curious

Reply #5 –
You can have 288 kbps frame sizes using freeformat encoding.

There cannot be 288 kbps frame sizes in standard MP3 because that's the way the format was designed. You might as well ask why you can't shift your car into the 3.5th gear, or go to track 100 on an audio CD.

Just Curious

Reply #6 –
Quote
SebastianG

your table is wrong, 128kbps is in the +16kbps range that's why 128kbps will never be considered "high bitrate",  anything above 128kbps is wrong
(128+16=144 ... not 160kbps)
[a href="index.php?act=findpost&pid=244885"][{POST_SNAPBACK}][/a]


yup, it was an unintentional copy&paste bug. I just fixed it.

Sebastian

Just Curious

Reply #7 –
Good analogy....analogy
No one can be told what Ogg Vorbis is...you have to hear it for yourself
- Morpheus