Converting a 5.1 track to mp3 DPII using Belight

[datauser]

I studied all the info here, but could not find anything about the Control rear channel filtering option using BeLight GUI to convert a 5.1 track to 192kbp/s joint stereo ouput mode to DPII.

Should I enable this option in Belight and if so is any sound information lost? Thanks.

[tebasuna51]

When check the 'Control Rear Channel Filtering' box in BeLight Azid Settings the parameter -f 1 is passed to Azid decoder.

The help for this parameter is:

-f BOOL, --rear-filter=BOOL (dll)
---------------------------

Default: off

This option controls rear-channel filtering in 2/0 output mode. The
filter is a 2nd order Butterworth filter with at -3 dB point at 7
kHz. There are two major applications for this feature:

o To provide proper Pro Logic downmix of the rear channels

o Phasing-problems in the downmix (washy sound) caused by the rear
channel downmix into the L R channels.

Usually the rear channels are phased 90 deg in respect of the front
channels prior or inside the ac3 encoder. This is done to avoid
phasing problems when downmixing the program contents to two
channels. Some sources do not provide this shifting, and thus this
feature is added.

The filter provides an increasing phase shift according to
frequency. It is 90 deg at 7kHz.

Then, if source AC3 5.1 is Dolby compliant (rear channels already shifted), you don't need check this option.

[datauser]

When would the viable need arise to enable this option when doing an conversion to avoid these "washy sound" phasing problems as you quote. Maybe if your input is a 2 channel ac-3 source and you are re-converting to 5.1 or inputting an 2.0 ac-3 source to convert to 2.0 channel mp3 mode outputted to a DPII mix?

This is a really interesting subject technically! Thankyou.

[tebasuna51]

...Maybe if your input is a 2 channel ac-3 source and you are re-converting to 5.1 or inputting an 2.0 ac-3 source to convert to 2.0 channel mp3 mode outputted to a DPII mix?

When input is 2.0 don't exist rear channels to shift.

When you upmix a 2.0 to 5.1 you need use a method than shift the rear channels to be Dolby compliant.