Re: [SoX-devel] [ sox-Bugs-2949976 ] Non-reproducable rounding errors in conversion to Mu-Law

[Doug C. <idi...@us...>]

This is the expected behavior when reducing bit-depth from 16 to 14 bits.
SoX will dither the result to try to reduce the audible effects of the
bit-depth reduction. With the -D flag, you can disable dither.

On Thu, Feb 11, 2010 at 1:11 PM, SourceForge.net <no...@so...>wrote:

> Bugs item #2949976, was opened at 2010-02-11 21:11
> Message generated for change (Tracker Item Submitted) made by amigalemming
> You can respond by visiting:
>
> https://sourceforge.net/tracker/?func=detail&atid=110706&aid=2949976&group_id=10706
>
> Please note that this message will contain a full copy of the comment
> thread,
> including the initial issue submission, for this request,
> not just the latest update.
> Category: None
> Group: None
> Status: Open
> Resolution: None
> Priority: 5
> Private: No
> Submitted By: Amiga Lemming (amigalemming)
> Assigned to: Nobody/Anonymous (nobody)
> Summary: Non-reproducable rounding errors in conversion to Mu-Law
>
> Initial Comment:
> $ sox -V -V ramp.ul ramp.s16
> sox: SoX v14.3.0
> time:  Sep 28 2009 03:25:07
> uname: Linux 2.6.22.19-0.4-default #1 SMP 2009-08-14 02:09:16 +0200 i686
> gcc:   4.2.1 (SUSE Linux)
> arch:  1248 48 44 L OMP
> sox WARN raw: `ramp.ul': sample rate not specified; trying 8kHz
> sox WARN raw: `ramp.ul': # channels not specified; trying mono
>
> Input File     : 'ramp.ul'
> Channels       : 1
> Sample Rate    : 8000
> Precision      : 14-bit
> Duration       : 00:00:00.03 = 256 samples ~ 2.4 CDDA sectors
> File Size      : 256
> Bit Rate       : 64.0k
> Sample Encoding: 8-bit u-law
> Reverse Nibbles: no
> Reverse Bits   : no
>
> Output File    : 'ramp.s16'
> Channels       : 1
> Sample Rate    : 8000
> Precision      : 14-bit
> Duration       : 00:00:00.03 = 256 samples ~ 2.4 CDDA sectors
> Sample Encoding: 16-bit Signed Integer PCM
> Endian Type    : little
> Reverse Nibbles: no
> Reverse Bits   : no
> Comment        : 'Processed by SoX'
>
> sox INFO sox: effects chain: input      8000Hz 1 channels 14 bits (multi)
> sox INFO sox: effects chain: output     8000Hz 1 channels 14 bits (multi)
>
> $  sox ramp.s16 ramp-recons.ul
> sox WARN raw: `ramp.s16': sample rate not specified; trying 8kHz
> sox WARN raw: `ramp.s16': # channels not specified; trying mono
>
> Now
> $ cmp ramp.ul ramp-recons.ul
> reports a difference for byte no. 128, but this is not the problem, since
> it is due to zero having two representations in Mu-law.
> The problem is that at the end of ramp-recons.ul I see sometimes 0xf4
> instead of 0xf5 or 0xfe instead 0xff.
> It is not reproducable.
> I think the basic property should hold, that conversion from Mu-law to 16
> bit integers and back must reproduce the original mu-law data.
>
>
> ----------------------------------------------------------------------
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> You can respond by visiting:
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> https://sourceforge.net/tracker/?func=detail&atid=110706&aid=2949976&group_id=10706
>
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