IPB

Welcome Guest ( Log In | Register )

enhanced aac+ to aac lc
wind
post Nov 2 2012, 09:53
Post #1





Group: Members
Posts: 10
Joined: 1-November 12
Member No.: 104229



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...
or
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
Go to the top of the page
+Quote Post
 
Start new topic
Replies
Dynamic
post Nov 2 2012, 19:20
Post #2





Group: Members
Posts: 812
Joined: 17-September 06
Member No.: 35307



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.
Go to the top of the page
+Quote Post
wind
post Nov 3 2012, 15:14
Post #3





Group: Members
Posts: 10
Joined: 1-November 12
Member No.: 104229



QUOTE (Dynamic @ Nov 2 2012, 19:20) *
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.


Thank you Dynamic, you mean i can not modify the C code to sample at the original sample rate, i only can upsample the output file of the decoder ?
you are right, the SBR part in the enhanced aac+ decoder does the upsample, use QMF filter
about the resample software, how about the Adobe Audition software?which one is better?
i used the 'resample' command in matlab, but i am not sure about the 'order' value,if order is not correct, the quality may be not good.
Go to the top of the page
+Quote Post

Posts in this topic


Reply to this topicStart new topic
1 User(s) are reading this topic (1 Guests and 0 Anonymous Users)
0 Members:

 



RSS Lo-Fi Version Time is now: 15th September 2014 - 05:13