[LAU] Record levels lower in Alsa than Jack
rosegardener at freeode.co.uk
Sat Nov 7 08:03:17 CET 2020
On Fri, 6 Nov 2020 20:19:02 -0500 "Tim E. Real" wrote:
> On 11/6/20 10:06 AM, John Murphy wrote:
> > On Fri, 6 Nov 2020 15:07:43 +0100 Fons Adriaensen wrote:
> >> On Fri, Nov 06, 2020 at 01:22:42PM +0000, John Murphy wrote:
> >>> Then sox stat shows min/max amplitude +/- 0.5 for the wav capture and
> >>> +/- 0.9 for the wav converted from w64. The converted file looks good
> >>> in my editor too.
> >> Still doesn't explain the difference, unless I'm missing something...
> > There's a loss of precision in the conversion process. Both the original
> > recordings show 25 bit precision and the file sizes are the same (3.8MB).
> > The converted file is only 16 bit and is 1.9MB. It sounds (and looks)
> > louder. I doubt I could tell any loss of quality. Not explaining it.
> > Just providing some facts. :)
> Maybe this is relevant?
> According to my package manager, sox depends on libsndfile.
> On the libsndfile website:
> it talks about normalization:
> "When converting between integer data and floating point data, different
> rules apply.
> The default behaviour when reading floating point data (sf_read_float()
> or sf_read_double ())
> from a file with integer data is normalisation. Regardless of whether
> data in the file
> is 8, 16, 24 or 32 bit wide, the data will be read as floating point
> data in the range [-1.0, 1.0].
> Similarly, data in the range [-1.0, 1.0] will be written to an integer
> PCM file so that
> a data value of 1.0 will be the largest allowable integer for the
> given bit width.
> This normalisation can be turned on or off using the sf_command
> <http://www.mega-nerd.com/libsndfile/command.html> interface"
> I recall observing that this normalization does tend to make the result
> Could this be what is being observed?
That would seem to explain it and the output of sndfile-info appears
to confirm (see my reply to Chris). Quite surprised it does that extra
thing for me.
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