Low latency codecs Options

[knutinh]

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on narrow frequency bands, suitable for some masking stuff, but exploiting temporal correlation could be done against a historical reference (not introducing significant delay)?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

[saratoga]

but exploiting temporal correlation could be done against a historical reference (not introducing significant delay)?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.

[knutinh]

Most codecs don't really do this though, since its quite difficult in practice.

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

-k

[saratoga]

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".

[knutinh]

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

[Garf]

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.

[knutinh]

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)

[googlebot]

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).