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Topic: bock type,mixed block and intensity stereo in mp3 (Read 2149 times) previous topic - next topic
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bock type,mixed block and intensity stereo in mp3

Hi All,

            I am a bit confused with few things in MP3 i.e. MPEG-1 LAYER 3 format. The confusion is about three things:

1.   Block type.
2.   Mixed block
3.   Intensity stereo

Now the problem is:

I know that the 576 frequency lines are divided in 32 sub bands. Then there is one more grouping of scale factor bands, which depends upon long blocks and short blocks. Long and short blocks are based on values of block type and mixed block. Here I have problem.
Now when we do re-quantization while decoding a MP3 we first check if the 576 frequency lines fall completely in short blocks or long blocks. If all 576 frequency lines are falling in short or long blocks then it is very easy to do the re-quantization as there is no mixing.
When there is a mixed block which means long and short both we had 36 frequency lines falling in long block section and rest 540 in short blocks.

My question is that here Scale factor bands division has only role to play for the different scaling values?? Right??

Now another question is about intensity stereo. First thing is that in case of intensity stereo I am not able to understand the bit format.
How do we get is_pos where it lies in the main data. I read N number of documents in which they say that right/left channel keeps the value of is_pos in rzero region but I am not able to understand it from there.
Does anyone has any document which gives a better idea about intensity stereo and its processing (if there are some images explaining intensity stereo that would be nice as I am not able to visualize this stuff with help of textual explanation in various documents)?

Also one more thing is that if there is someone can explain mapping between the 32 sub bands and 21(long blocks)/(39 short blocks) scale factor bands in the case of only long, only short and mixed block case??

Thanks
-R/\\/I-