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enhanced aac+ to aac lc
post Nov 2 2012, 09:53
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Hi, everyone, has there anybody used enhanced aac+ code(TS 26.410) to encode/decode only aac lc ,without sbr?

I modified the encoder of the enhanced aac+, ,there is no sbr, then when the decoder decode the new .3gp file ,no sbr is decoded, but the outout sample rate is 1/2 downsampled, because aac lc works at 1/2 sample rate, the sbr works at original sample rate, and in the decoder ,it is sbr make it become to original sample rate, but now there is no sbr.
Does anyone know how to make the sample rate of decoder output same as the original input file sample rate, i tried to modify the encoder to encode at original sample rate,but there will be no sound, and if i use 1/2 sample rate .3gp & modify the decoder to change the sample rate and frame size, the sound will sound strange...
is that ok if i upsample the new decoder output file (1/2 sample rate ) through matlab?

Thanks in advance.

This post has been edited by wind: Nov 2 2012, 10:29
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post Nov 2 2012, 19:20
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What you see is to be expected. AFAIK, the only way to decode the LC part is at the half sampling rate because the inverse transform will only produce the number of samples that went into the original MDCT. (Out of interest, the old mp3pro files used MP3 at half the sampling rate, i.e. MPEG-2 layer 3, plus SBR for the upper half and a normal MP3 decoder without MP3Pro features would only produce the lower half).

I believe you need to resample (and I think that's what a AAC+ decoder does) though you'll probably find an app like foobar2000 (Windows) or SoX (command line multiplatform) does a good job of resampling and much faster than MATLAB, last I heard.
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