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Low latency codecs
knutinh
post Apr 27 2011, 07:35
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What are the choices for low latency codecs, and what is the fundamental information/perceptual trade-off?

I see that large block sizes are needed to do operations on narrow frequency bands, suitable for some masking stuff, but exploiting temporal correlation could be done against a historical reference (not introducing significant delay)?

-k
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saratoga
post Apr 27 2011, 07:51
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QUOTE (knutinh @ Apr 27 2011, 02:35) *
but exploiting temporal correlation could be done against a historical reference (not introducing significant delay)?


Most codecs don't really do this though, since its quite difficult in practice.
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knutinh
post Apr 27 2011, 08:56
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QUOTE (saratoga @ Apr 27 2011, 08:51) *
Most codecs don't really do this though, since its quite difficult in practice.

http://en.wikipedia.org/wiki/DPCM
patented in 1950?

-k
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saratoga
post Apr 28 2011, 03:21
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QUOTE (knutinh @ Apr 27 2011, 03:56) *
QUOTE (saratoga @ Apr 27 2011, 08:51) *
Most codecs don't really do this though, since its quite difficult in practice.

http://en.wikipedia.org/wiki/DPCM
patented in 1950?


Try encoding real music losslessly with DPCM and see how much compression you get. You'll see why I said its "difficult".
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knutinh
post Apr 28 2011, 09:55
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QUOTE (saratoga @ Apr 28 2011, 04:21) *
Try encoding real music losslessly with DPCM and see how much compression you get. You'll see why I said its "difficult".

This confuses me. Is not "all" music lowpass in nature (at least as a long-term statistic)? Is not DPCM practically a high-pass pre-whitening filter/low-pass predictor?

If music in general is somewhat predictable (just like the weather tends to be like the weather the day before), I would have guessed that a simple, primitive predictor would be better than nothing.

-k

This post has been edited by knutinh: Apr 28 2011, 10:05
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Garf
post Apr 28 2011, 11:35
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QUOTE (knutinh @ Apr 28 2011, 10:55) *
This confuses me. Is not "all" music lowpass in nature (at least as a long-term statistic)? Is not DPCM practically a high-pass pre-whitening filter/low-pass predictor?

If music in general is somewhat predictable (just like the weather tends to be like the weather the day before), I would have guessed that a simple, primitive predictor would be better than nothing.


"Better than nothing" is still a far cry from what the codecs achieve now. The T/F transformations they use also exploits the property you mentioned, and hence temporal correlation (but seen from a frequency perspective). Getting more out of that by exploiting correlation between transformed blocks is difficult.
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knutinh
post Apr 28 2011, 15:07
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QUOTE (Garf @ Apr 28 2011, 12:35) *
QUOTE (knutinh @ Apr 28 2011, 10:55) *
This confuses me. Is not "all" music lowpass in nature (at least as a long-term statistic)? Is not DPCM practically a high-pass pre-whitening filter/low-pass predictor?

If music in general is somewhat predictable (just like the weather tends to be like the weather the day before), I would have guessed that a simple, primitive predictor would be better than nothing.


"Better than nothing" is still a far cry from what the codecs achieve now. The T/F transformations they use also exploits the property you mentioned, and hence temporal correlation (but seen from a frequency perspective). Getting more out of that by exploiting correlation between transformed blocks is difficult.

So a more precise answer to my initial questions would perhaps be:
1. Lossless audio compression is usually possible, and will give you 2:1 or so for a substantial delay
2. Lossy audio compression is usually possible and may give you 10:1 or so for a substantial delay
3. Very low latency audio compression is usually possible but will either give very poor compression (lossless) or very poor quality:bitrate (lossy)
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googlebot
post Apr 28 2011, 16:10
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QUOTE (knutinh @ Apr 28 2011, 15:07) *
3. Very low latency audio compression is usually possible but will either give very poor compression (lossless) or very poor quality:bitrate (lossy)


The last HA listening test tells a different story (see Opus).
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Posts in this topic
- knutinh   Low latency codecs   Apr 27 2011, 07:35
- - saratoga   QUOTE (knutinh @ Apr 27 2011, 02:35) but ...   Apr 27 2011, 07:51
|- - knutinh   QUOTE (saratoga @ Apr 27 2011, 08:51) Mos...   Apr 27 2011, 08:56
|- - saratoga   QUOTE (knutinh @ Apr 27 2011, 03:56) QUOT...   Apr 28 2011, 03:21
|- - knutinh   QUOTE (saratoga @ Apr 28 2011, 04:21) Try...   Apr 28 2011, 09:55
|- - Garf   QUOTE (knutinh @ Apr 28 2011, 10:55) This...   Apr 28 2011, 11:35
|- - knutinh   QUOTE (Garf @ Apr 28 2011, 12:35) QUOTE (...   Apr 28 2011, 15:07
|- - googlebot   QUOTE (knutinh @ Apr 28 2011, 15:07) 3. V...   Apr 28 2011, 16:10
||- - Garf   QUOTE (googlebot @ Apr 28 2011, 17:10) QU...   Apr 28 2011, 16:15
||- - googlebot   The OP asked for low delay codecs. Opus at 22 ms i...   Apr 28 2011, 17:28
|- - Garf   QUOTE (knutinh @ Apr 28 2011, 16:07) 3. V...   Apr 28 2011, 16:13
- - C.R.Helmrich   QUOTE (knutinh @ Apr 27 2011, 08:35) ...e...   Apr 27 2011, 12:06
- - Garf   In the case of AAC, both Main and LTP profile went...   Apr 27 2011, 13:10
- - NullC   QUOTE (knutinh @ Apr 26 2011, 22:35) What...   Apr 28 2011, 03:08
|- - knutinh   QUOTE (NullC @ Apr 28 2011, 04:08) Maskin...   Apr 28 2011, 10:04
||- - Garf   QUOTE (knutinh @ Apr 28 2011, 11:04) Can ...   Apr 28 2011, 11:30
||- - _mē_   QUOTE (Garf @ Apr 28 2011, 12:30) QUOTE (...   Apr 28 2011, 15:00
||- - Garf   QUOTE (_mē_ @ Apr 28 2011, 16:00) A bit O...   Apr 28 2011, 16:07
|- - knutinh   QUOTE (NullC @ Apr 28 2011, 04:08) Maskin...   Apr 30 2011, 18:58
|- - Garf   QUOTE (knutinh @ Apr 30 2011, 19:58) ...   May 1 2011, 17:09
- - 2Bdecided   NICAM. But it's hardly efficient! Cheer...   Apr 28 2011, 12:03


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