Hi Folks! Just needed some information on some of the schemes that are used to implement DeQuantization of audio samples. The scheme that I know is DeQuantization using a look-up table of 8192 by storing the value of y^(4/3) in the table and using y as the index to access these values. Is it possible to eliminate the Look-up table totally without much computational effort ..since calculating value of y^(4/3) using binomial approx is computationally heavy .......instead can it be done by using something like approximating the curve using a line or something like that...(i.e.simple slope calculation)... Can someone who has worked AAC throw light on the same? Thanks in advance, Siddharth

# Query on DeQuantization of MPEG-4 AAC Decoder

Started by ●April 28, 2005

Reply by ●April 28, 20052005-04-28

Please refer the FAAD2 code. It used only 1k memory for that look-up table. For your reference. --- Siddharth Nag <siddharth.nag@sidd...> wrote: --------------------------------- Hi Folks! Just needed some information on some of the schemes that are used to implement DeQuantization of audio samples. The scheme that I know is DeQuantization using a look-up table of 8192 by storing the value of y^(4/3) in the table and using y as the index to access these values. Is it possible to eliminate the Look-up table totally without much computational effort ..since calculating value of y^(4/3) using binomial approx is computationally heavy .......instead can it be done by using something like approximating the curve using a line or something like that...(i.e.simple slope calculation)... Can someone who has worked AAC throw light on the same? Thanks in advance, Siddharth To _______________________________________________________________________ Yahoo!_qlHc KOeq250MBAHh]http://tw.promo.yahoo.com/mail_new/index.html

Reply by ●May 2, 20052005-05-02

Hi Sidharth, If memory is your problem in keeping a look up table, use the following approach. Keep a look up table of say 1024 elements for x = y ^ (4/3). For values more than 1023, use the following. x = (16/16) y ^ (4/3) = (16/ 2^4 *) y ^ (4/3) = 16 * ( (y/8) ^ (4/3)) ( (y/8) ^ (4/3))is available in the 1024 element look up table and multiply by 16 to get an approximate value. The only issue is you lose accuracy and there are methods where you can get exact accuracy by using interpolating the nearest two values obtained by above method. Regards, Tony -----Original Message----- From: audiodsp@audi... [mailto:audiodsp@audi...] On Behalf Of Siddharth Nag Sent: Thursday, April 28, 2005 5:26 PM To: audiodsp@audi... Subject: [audiodsp] Query on DeQuantization of MPEG-4 AAC Decoder Hi Folks! Just needed some information on some of the schemes that are used to implement DeQuantization of audio samples. The scheme that I know is DeQuantization using a look-up table of 8192 by storing the value of y^(4/3) in the table and using y as the index to access these values. Is it possible to eliminate the Look-up table totally without much computational effort ..since calculating value of y^(4/3) using binomial approx is computationally heavy .......instead can it be done by using something like approximating the curve using a line or something like that...(i.e.simple slope calculation)... Can someone who has worked AAC throw light on the same? Thanks in advance, Siddharth