[flac-dev] Autocorrelation precision insufficient

Brian Willoughby brianw at audiobanshee.com
Mon Jun 28 07:45:23 UTC 2021


I should probably start a new subject, but I have related questions. Please don't feel obligated to answer ... I'm just curious.

1) What would affect the ability of an embedded FLAC firmware to decode certain files?

Is it possible that the SD702 is not capable of processing complex predictors of higher orders?

Could it be as simple as absence (or requirement?) of mid-side encoding? (this doesn't seem that likely)

2) Is there a strict definition of the 9 levels of FLAC coding such that the level would precisely determine the predictor?

I haven't looked at the source in ages, but it seems like you're saying that the compression level might map to exact choices for model/predictor.

3) Can you explain why the encoded file should be exactly the same across different processors or implementations? I'm still fuzzy on the details, but it seems like the exact bits could still vary even with the same model - i.e. "exhaustive" implies that different implementations might stop at different points along the way.


On Jun 27, 2021, at 23:34, Martijn van Beurden <mvanb1 at gmail.com> wrote:
> different residual encoding method in version 1.2.0, in 2007. No other
> changes to the format and thus decoding were introduced after 1.0.
> The different compression levels increase one of two things: how much
> effort to spend finding the best model, and how complex a predictor to use.
> The first, the effort finding the best predictor, slows down the
> encoding but not
> decoding. These are options like adding apodizations and exhaustive model order
> and precision search. With these settings, the encoder tries various models and
> picks the one that fits best. The second, how complex of a predictor
> to use, does
> affect decoding performance. There are only three parameters here:
> whether to use
> a fixed or non-fixed predictor, how large the maximum model order is and whether
> mid-side encoding is used.
> The change I propose is a change in the way the encoder does the modelling.
> When this modelling is done with more precision, this slows down encoding,
> but it does not change anything in the way decoding is done. It just changes the
> 'representation' that needs to be decoded, but this decoding process does not
> become more complex.

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