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--xlevel With Mpc?
post Oct 26 2002, 04:35
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Can someone tell me the plusses and minuses of using -xlevel? There seems to be a significant minority of MPC user who rely on this switch. The ducumentation is pretty sparce, something about an alternate clipping prevention scheme.

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post Oct 26 2002, 13:22
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Okay, here again is a summary i posted in an older thread:

What is the --xlevel switch good for?

> It prevents the internal clipping error in MPC SV7 (current StreamVersion).
> I think, when the codec was designed, Andree Buschmann couldn't imagine
> that one day the CDs would be as heavily overdriven as they are now.

Quoting Frank Klemm:

> This error is a design error of SV7. It was underestimated that
> CDs can be permanently clipped with hundreds of clipped
> samples at the one end jumping directly to some hundred
> samples clipped on the other end. Affected files have a serious
> degeneration of audio quality behind. If you would press vinyl
> with such a level the playtime will be around 8...9 minutes per
> page due to the huge excursions.
> Normally such files should be reconstructed using some audio restauration
> software to reduce distortions below 7%.
> Please also note that most sound cards can't handle full scale
> audio. They distore below 0 dB, you don't need digital overloads.

What happens during internal clipping, quoting Andree Buschmann:

> Let's say the scalefactor range is not enough, then the subband-samples
> will exceed the allowed range and the samples will be hardclipped!
> The decoder cannot reconstruct the original waveform (even if gaining it by -x dB).

What the --xlevel switch does to prevent this, quoting Frank Klemm:

> It uses scale factors outside 0...63, which is mostly possible by
> relative addressing (instead of the 6 bit absolute addressing).
> The first solution [hard-clipping] is compatible with all decoders,
> but generates higher coding errors, the second solution [--xlevel]
> can only be played by Klemm-based decoders (which support scale from -4...127).

My advice is to use --xlevel, the compatibility is really not such a problem. All newer decoders are compatible. The last incompatible decoder is from mid-2001.
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