[Flac-dev] Re: nice idea

[Hod McWuff]

A good first run. I wonder, though, what the distribution of block sizes
looks like, and what the magnitude of residual is as a function of block
index.

I'd honestly expect a more significant improvement for either algorithm.

On Sat, 2002-10-19 at 11:13, Miroslav Lichvar wrote:
> On Thu, Oct 17, 2002 at 09:51:02AM -0500, Brady Patterson wrote:
> > 
> > Okay, I deleted most of this thread, so I was waiting for another message to
> > respond to, so unfortunately this will be out of place in the thread.
> > 
> > This is in response to Miroslav's idea about variable block sizes.  I may be a
> > bit out of my league here as I'm just starting to look at how the actual
> > encoding gets done.  But it seems to me that you could make a decent guess
> > about when something "new" happens based on the second derivative of the signal
> > (where the first derivative is the difference between a given sample and the
> > previous, and the second is you-get-the-idea).
> > 
> > Here's my rationale: high-amplitude, high-frequency sections are the hard ones
> > to encode, or at least will work best in their own frame.  Those
> > characteristics imply a high first derivative.  You want to put such sections
> > in their own block, and boundaries of such blocks will be where the second
> > derivative is relatively high.
> > 
> > Okay, that's not quite right, since the first derivative will be negative about
> > half the time, and large negative has the same effect as lange positive.  So I
> > think what you really want is the first derivative of the absolute value of the
> > first derivative.
> > 
> > Then there's the question of where to put the boundaries.  Some trial-and-error
> > is probably the best approach here.  For files on which the above formula is
> > consistently high, it will probably be desirable to set the limit high to avoid
> > too much frame overhead.
> > 
> > Hope this was interesting and/or useful :) .
> 
> Well, i took 10 CD and test my primitive implementations of these
> algos. Here are my results:
> 
>       size                            encoding time
> (0)   6401778544  1.0000            
> (1)   4193699407  0.6551  1.0000      1.00
> (2)   4180011683  0.6529  0.9967      1.18
> (3)   4186509853  0.6540  0.9983      1.15
> 
> "best" CD:
> (0)    503448568  1.0000  
> (1)    349525363  0.6942  1.0000
> (2)    347167639  0.6896  0.9933
> (3)    347864119  0.6910  0.9952
> 
> "best" track:
> (0)     44111804  1.0000
> (1)     28091683  0.6368  1.0000
> (2)     27769870  0.6295  0.9885
> (3)     27864205  0.6317  0.9919
> 
> where:
> (0) wav files
> (1) flac files, fixed blocksize 4608
> (2) flac files, variable blocksize, "lpc idea"
> (3) flac files, variable blocksize, watching average of absolute
>     values of first and second derivative
> 
> 
> -- 
> Miroslav Lichvar
> 
> 
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