PDA

View Full Version : Bit-correct digital output



Steinar Bjaerum
2005-02-28, 17:13
Hi.

I investigated the bit-correctness of the digital output of Squeezebox using
the DTS encoded as WAV method:

I downloaded a DTS sample file encoded as a 44.1kHz WAV file.
I made a second version of the file where the sign was inverted for all
samples.
I connected the digital out of my Squeezebox to my hometheater receiver.

Results when playing the WAVs on Squeezebox:
File with original sign results in only noise being played.
File with inverted sign is identified as DTS by my receiver and plays
correctly.
Conclusion: Squeezebox has bit-correct output except for inverted sign
(inverted phase).

To investigate if it is possible to get bit-correct output without phase
inversion, I modified the volume function in Squeezebox.pm as suggested by
Sean Adams. That is, changing the volume coefficient from 8000 to 7FFF. With
this change, none of the files played correctly.

As a conclusion, Squeezebox is capable of bit-correct digital output except
for phase inversion. Bit-correct output without phase inversion is not
possible. Well, it is possible by adding some software which inverts the
sign of the PCM samples sent to the Squeezebox.

You could also take a look at:
http://www4.head-fi.org/forums/showthread.php?p=1264080

Steinar

Ed Atlee
2005-03-02, 09:16
"Steinar Bjaerum" <steinar.bjaerum (AT) online (DOT) no>
wrote in message news:200503010013.j210DFgm025992 (AT) mail42 (DOT) nsc.no...
> Hi.
>
> I investigated the bit-correctness of the digital output of Squeezebox
using
> the DTS encoded as WAV method:
>
> I downloaded a DTS sample file encoded as a 44.1kHz WAV file.
> I made a second version of the file where the sign was inverted for all
> samples.
> I connected the digital out of my Squeezebox to my hometheater receiver.
>
> Results when playing the WAVs on Squeezebox:
> File with original sign results in only noise being played.
> File with inverted sign is identified as DTS by my receiver and plays
> correctly.
> Conclusion: Squeezebox has bit-correct output except for inverted sign
> (inverted phase).

This was not what I experienced, unless for some reason the entire DTS CD
that I had was phase-inverted and I didn't know it, either originally or by
Exact Audio Copy. Or my preamp just accepts it anyway? I haven't played it
in a couple of months, so I'll check it again. I'm using 5.4.0 now on Win
XP.

How did you invert the sign to create the second version of the file?

Ed