Reconstructing AAC CPE

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Revision as of 22:55, 6 March 2006 by Multimedia Mike (talk | contribs) (Reconstruction Process)
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Part of Understanding AAC

This page describes the process of reconstructing PCM data based on the decoded CPE parameters in an AAC bitstream. For the moment, this description focuses on what is necessary to reconstruct low complexity (LC) profile data.

Reconstruction Process

 +-specrec.c:reconstruct_channel_pair()
   +-specrec.c:allocate_channel_pair()
   +-specrec.c:quant_to_spec()
   +-pns.c:pns_decode()
   +-ms.c:ms_decode()
   +-is.c:is_decode()
   +-ic_predict.c:ic_prediction() (main profile)
   +-ic_predict.c:pns_reset_pred_state() (main profile)
   +-(processing that is specific LTP & LD profiles)
   +-tns.c:tns_decode_frame()
   +-drc.c:drc_decode()
   +-filtbank.c:ifilter_bank()
     +-filtbank.c:imdct_long()
     +-mdct.c:faad_imdct()
   +-ssr.c:ssr_decode()
   +-lt_predict.c:lt_update_state()
   +-sbr_dec.c:sbrDecodeInit()
   +-sbr_dec.c:sbrDecodeCoupleFrame()

reconstruct_channel_pair(2 ic_streams, 2 spec_data arrays(16 bit ints))

 declare 2 1024-element float arrays for spectral coefficients (spec_coeff1 and spec_coeff2)
 quant_to_spec(ics1, spec_data1, ics1)
 quant_to_spec(ics2, spec_data2, ics2)
 if ics1.ms_mask_present
   pns_decode(ics1, ics2, spec_coef1, spec_coeff2)
 else
   pns_decode(ics1, spec_coef1)
   pns_decode(ics2, spec_coef2)
 ms_decode(ics1, ics2, spec_coef1, spec_coef2)
 is_decode(ics1, ics2, spec_coef1, spec_coef2)
 // main profile decoding
 // LTP decoding
 tns_decode(ics1, spec_coeff1)
 tns_decode(ics2, spec_coeff2)
 // DRC stuff
 ifilter_bank(ics1, spec_coeff1)
 ifilter_bank(ics2, spec_coeff2)
 save window shape for next frame (I thought frames were independent)
 // LTP stuff
 // SBR stuff

allocate_channel_pair()

quant_to_spec()

pns_decode()

ms_decode()

is_decode()

ic_prediction()

pns_reset_pred_state()

tns_decode_frame()

drc_decode()

ifilter_bank()

ssr_decode()

lt_update_state()

sbrDecodeInit()

sbrDecodeCoupleFrame()