[Mp4-tech] [Audio] Intensity Stereo and M/S stereo

Ravi Kiran rkiran emuzed.com
Sun Jul 4 14:27:14 EDT 2004


A small correction in the pseudo code:
'if(ms_mask_present)' should be replaced with 'if(ms_mask_present = = 1)'
----- Original Message ----- 
From: "Ravi Kiran" <rkiran emuzed.com>
To: "Saptarshi Ghosh" <saptarshi_bec yahoo.com>; <mp4-tech lists.mpegif.org>
Sent: Sunday, July 04, 2023 1:15 PM
Subject: Re: [Mp4-tech] [Audio] Intensity Stereo and M/S stereo
> Dear Saptarshi,
>     Both M/S and IS stereo cannot be applied in a single scalefactor band.
> M/S and IS are mutually exclusive for a scalefactor band.
>     For M/S stereo to be appled to a scalefactor band all the following
> conditions should be met:
>     1. Either ms_used should be 1 for that scalefactor band or
> ms_mask_present should be 2
>     2. The given scalefactor band should not be coded with INTENSITY_HCB
or
> INTENSITY_HCB2
>
>     However, there can be a case in which ms_mask_present >= 1 and the
> scalefactor band is coded with INTENSITY_HCB or INTENSITY_HCB2. In this
case
> M/S stereo cannot be applied because the second condition stated above
> fails.
>     However, IS can be applied to this scale factor band. The dependency
> between the code book used, ms_used and phase of the stereo is given in
the
> pseudo code below:
>     if(sfb_cb[sfb] == INTENSITY_HCB)
>     {
>          if(ms_mask_present)
>          {
>               phase  =  (1-2*ms_used[sfb]);
>          }
>          else
>          {
>               phase = 1;
>          }
>     }
>
>     if(sfb_cb[sfb] == INTENSITY_HCB2)
>     {
>          if(ms_mask_present)
>          {
>               phase  =  -(1-2*ms_used[sfb]);
>          }
>          else
>          {
>               phase  =  -1;
>          }
>     }
>
> If ms_mask_present is 2 then all ms_used should be initialized to 1 in the
> above code. Hope things are clear now.
>
> Regards
> Ravi Kiran.
> ----- Original Message ----- 
> From: "Saptarshi Ghosh" <saptarshi_bec yahoo.com>
> To: <mp4-tech lists.mpegif.org>
> Sent: Friday, July 02, 2023 6:24 PM
> Subject: [Mp4-tech] [Audio] Intensity Stereo and M/S stereo
>
>
> > Hi all,
> > Can anyone clarify the following doubt?
> >
> > Can BOTH Intensity stereo and M/S stereo be required
> > to be used on a single scalefactor band ? (it seems
> > yes, from the specifications which describes the
> > functions invert_intensity( ) to reverse the phase of
> > intensity if M/S has been used for a particular sfb)
> >
> > If yes, then it seems that a considerable number of
> > redundant operations will have to be done in case of a
> > sfb where both have been used. Since in M/S, we derive
> > the left and right channel info from what is
> > transmitted in the stream, and then in Intensity
> > stereo tool, we overwrite the info derived for the
> > right channel by
> >      right channel data = scale * left channel data
> > Thus the calculations done during M/S processing
> > become redundant.
> >
> > Could anyone help in this regand?
> > Regards,
> > Saptarshi.
> >
> >
> >
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