Skip to main content

Topic: Difference in MDCT for LTP (Read 3244 times) previous topic - next topic

0 Members and 1 Guest are viewing this topic.
  • pratheekp
  • [*][*]
Difference in MDCT for LTP
hi all,
        In case of AAC with LTP in decoder,after predicting the current frame by using the equation
    x_est(i) = ltp_coef*x_rec(i – M – ltp_lag)
we get the N predicted time samples(N,length of window transform)

After this we have to convert it to frequency domain using MDCT.. here can we use the same MDCT as in encoder for converting the time samples we read from the .wav file to f-domain, or is there any difference between the normal MDCT we use and the MDCT we use for LTP??
Please help

Regards
Pratheek

  • pratheekp
  • [*][*]
Difference in MDCT for LTP
Reply #1
somebody please reply

  • alexeysp
  • [*][*][*]
Difference in MDCT for LTP
Reply #2
I'm not an expert, but as far as I understand the specification, it should be the same transform that is used for conventional long blocks encoding.

If you are interested in actual implementation, you could take a look at the FAAC source code.
  • Last Edit: 09 September, 2011, 10:28:38 AM by alexeysp

  • coral
  • [*]
Difference in MDCT for LTP
Reply #3
hi all,
        In case of AAC with LTP in decoder,after predicting the current frame by using the equation
    x_est(i) = ltp_coef*x_rec(i – M – ltp_lag)
we get the N predicted time samples(N,length of window transform)

After this we have to convert it to frequency domain using MDCT.. here can we use the same MDCT as in encoder for converting the time samples we read from the .wav file to f-domain, or is there any difference between the normal MDCT we use and the MDCT we use for LTP??
Please help

Regards
Pratheek


In the decoder, don't you need to do IMDCT? Therefore you cannot used MDCT in the encoder.
Or I may not understand your question clearly