[prev in list] [next in list] [prev in thread] [next in thread] 

List:       mad-dev
Subject:    [mad-dev] III_requantize question
From:       rob () mars ! org (Rob Leslie)
Date:       2003-10-20 10:04:18
Message-ID: C4B48A13-02E4-11D8-AE5E-000A95823400 () mars ! org
[Download RAW message or body]

On Sunday, October 19, 2003, at 10:47  PM, Grigory Abuladze wrote:
> I am working with mad-0.15.0
> I hope someone may give me answer on this questions:
>
> 1. The result of this function III_exponents() in layer3.c file is
>    signed int exponents[39] array. My question - in which format
>    is result presented?

The resulting exponents represent multiples of 1/4 -- in other words, 
imagine a fixed binary point to the left of the two least significant 
bits.

> 2.
>       Xr = is^(4/3) * 2^(exp)       (sign not discussed)
>
>       What value exp can be and what step?
>       -88.5 <= exp <= 11.5, 0 <= is[i] <= 8207
>       are this equation true?

I calculate -81.5 <= exp <= 11.25 based on the theoretical limits of 
the requantization formula variables.

Also 0 <= is[i] <= 8206, although there is some debate over whether 
ISO/IEC 11172-3 actually permits values greater than 8191.

>       From III_requantize() it is look like step is 2^(1/4) - where 
> can I take this information?

Yes, from the requantization and scaling formula presented in ISO/IEC 
11172-3, the exponent may be a multiple of 1/4 depending on global_gain 
and, for short blocks, subblock_gain[w].

-- 
Rob Leslie
rob@mars.org


[prev in list] [next in list] [prev in thread] [next in thread]