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24bit PCM compress
yg2003618
post Nov 25 2010, 10:22
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anyone knows about how to compress 24bit PCM 48Khz audio, I know that most codecs process 16bit pcm. i want compress 24bit PCM at real time, 3:1 or 4:1 compress rate. who can help me? i know that subband adpcm maybe a choice. anyone knows more about that?

thanks alot.
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googlebot
post Nov 26 2010, 21:26
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It depends, if high dynamic range is a top priority (at the cost of others), then yes.

And especially regarding ultra low delay codecs: 144 samples per frame is such a tight limit for the set of possible filtering operations, maybe a higher "vertical" input resolution can help the encoder make better choices under these extreme circumstances. But that's only a guess.

This post has been edited by googlebot: Nov 26 2010, 21:28
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saratoga
post Nov 26 2010, 21:42
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QUOTE (googlebot @ Nov 26 2010, 15:26) *
It depends, if high dynamic range is a top priority (at the cost of others), then yes.

And especially regarding ultra low delay codecs: 144 samples per frame is such a tight limit for the set of possible filtering operations,


No thats the absolute limit assuming an infinitely fast processor, not the ancient arm7 core the OP is using. Realistically he probably has a fraction of that to work with.

QUOTE (googlebot @ Nov 26 2010, 15:26) *
maybe a higher "vertical" input resolution can help the encoder make better choices under these extreme circumstances. But that's only a guess.


I think thats unlikely. Hes using ARM7, which means 32 bit fixed point inputs to the encoder, no matter what the actual PCM is (since arm7 lacks dsp extensions for things like 16 bit multiplies). In practice, since he is using lossy anyway, the choice the input PCM format is likely to be of no consequence.
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googlebot
post Nov 26 2010, 21:54
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QUOTE (saratoga @ Nov 26 2010, 21:42) *
I think thats unlikely. Hes using ARM7, which means 32 bit fixed point inputs to the encoder, no matter what the actual PCM is (since arm7 lacks dsp extensions for things like 16 bit multiplies).


A 4 bit signal stays a 4 bit signal. A mandatory conversion to 32 bit int doesn't change that, neither for 16 bit or 24 bit. The samples are just padded with zeroes.

QUOTE (saratoga @ Nov 26 2010, 21:42) *
In practice, since he is using lossy anyway, the choice the input PCM format is likely to be of no consequence.


Could you please explain the inference? I don't understand it. Especially how it is supposed to refute to the paragraph you have cited.

This post has been edited by googlebot: Nov 26 2010, 22:22
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saratoga
post Nov 26 2010, 22:39
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QUOTE (googlebot @ Nov 26 2010, 15:54) *
Could you please explain the inference? I don't understand it. Especially how it is supposed to refute to the paragraph you have cited.


Thats because its not an inference; I wasn't really trying to refute anything you said, rather I was just diplomatically telling you thats not how it works. In your quote you broke up the paragraph at the wrong point, it should be the first sentence on its own, with the remainder being the second idea.

But anyway, what I was alluding to is that lossy encoders generally don't care about bit depth since they're never going to actually store anything as PCM except in their internal memory while they wait to process it. With that in mind, the only difference between 16 and 24 bit would be how they are actually implemented. Hence the second point, which was that since the processor had no good way to operate on 16 or 24 bit values, it would have to operate on 32 bit ones, and so it would feed all PCM sizes <= 32 bits down the same routines. This might not be the case on a 16 bit DSP though, where you might use separate routines depending on the input data (and hence might also have a reason to treat the calculations differently).
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Posts in this topic
- yg2003618   24bit PCM compress   Nov 25 2010, 10:22
- - Engelsstaub   You can use dBpoweramp or Foobar 2000. I'm cer...   Nov 25 2010, 10:37
|- - googlebot   QUOTE (Engelsstaub @ Nov 25 2010, 10:37) ...   Nov 25 2010, 11:12
|- - Engelsstaub   QUOTE (googlebot @ Nov 25 2010, 04:12) QU...   Nov 25 2010, 23:15
|- - googlebot   QUOTE (Engelsstaub @ Nov 25 2010, 23:15) ...   Nov 26 2010, 01:07
- - soiaf   WavPack (lossy/hybrid mode) will certainly handle ...   Nov 25 2010, 22:27
- - romor   ^ Can you believe this guy? Is that old D.R.I. log...   Nov 25 2010, 23:55
|- - Engelsstaub   QUOTE (romor @ Nov 25 2010, 16:55) ^ Can ...   Nov 26 2010, 04:14
- - yg2003618   thanks everyone, my project is using an ARM7 cpu t...   Nov 26 2010, 03:09
|- - saratoga   QUOTE (yg2003618 @ Nov 25 2010, 21:09) th...   Nov 26 2010, 05:57
|- - yg2003618   QUOTE (saratoga @ Nov 26 2010, 06:57) QUO...   Nov 26 2010, 07:17
|- - saratoga   QUOTE (yg2003618 @ Nov 26 2010, 01:17) QU...   Nov 26 2010, 16:59
- - yg2003618   Nero AAC may do 24bit compress, but i need source ...   Nov 26 2010, 03:20
- - Engelsstaub   Doesn't compressing a 24-bit file to a lossy c...   Nov 26 2010, 09:32
|- - knutinh   QUOTE (Engelsstaub @ Nov 26 2010, 09:32) ...   Nov 26 2010, 11:16
|- - googlebot   QUOTE (Engelsstaub @ Nov 26 2010, 09:32) ...   Nov 26 2010, 19:56
|- - knutinh   QUOTE (googlebot @ Nov 26 2010, 19:56) Wh...   Nov 26 2010, 20:56
- - Engelsstaub   Thanks for the explanation, knutinh. I failed to ...   Nov 26 2010, 14:52
- - [JAZ]   Mmm... 1152kbps for 24bit 48Khz is a mono signal. ...   Nov 26 2010, 19:10
- - googlebot   It depends, if high dynamic range is a top priorit...   Nov 26 2010, 21:26
|- - saratoga   QUOTE (googlebot @ Nov 26 2010, 15:26) It...   Nov 26 2010, 21:42
|- - googlebot   QUOTE (saratoga @ Nov 26 2010, 21:42) I t...   Nov 26 2010, 21:54
|- - saratoga   QUOTE (googlebot @ Nov 26 2010, 15:54) Co...   Nov 26 2010, 22:39
- - googlebot   I've read it again. Maybe you are right. Even ...   Nov 26 2010, 23:43
- - yg2003618   CELT is the answer! thank you, thank you every...   Nov 27 2010, 00:48


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