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Difference in MDCT for LTP
pratheekp
post Sep 3 2011, 06:21
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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
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pratheekp
post Sep 9 2011, 10:45
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somebody please reply
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alexeysp
post Sep 9 2011, 15:25
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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.


This post has been edited by alexeysp: Sep 9 2011, 15:28
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coral
post Jan 22 2012, 00:40
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QUOTE (pratheekp @ Sep 3 2011, 06:21) *
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
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