Vorbis - Sep 2001 - lowpass option (Was: RE: channel coupling in rc2)

I would very much like a lowpass option because for FM radio broadcasting I
don't want to encode frequencies above 15khz.  I'm waiting for this
option
before switching to ogg from mp3(lame).

Ross.
> -----Original Message-----
> From: owner-vorbis@xiph.org [mailto:owner-vorbis@xiph.org]On Behalf Of
> Gian-Carlo Pascutto
> Sent: Tuesday, 4 September 2001 01:46
> To: vorbis@xiph.org
> Subject: Re: [vorbis] channel coupling in rc2
> 
> 
> 
> On Mon, 3 Sep 2001, Greg Wooledge wrote:
> 
> > Gian-Carlo Pascutto (gcp@sjeng.org) wrote:
> >
> > > What I've been wondering about is why you would want to pick
the
> > > channel coupling mode yourself.
> >
> > The same reason we want to pick the lowpass cutoff 
> frequency ourselves
> > (hint, hint).
> 
> Same question, why?
> 
> If you think the current lowpass is too low for your hearing then the
> solution is more likely a higher *bitrate* than a higher lowpass.
> 
> My fear with allowing people to select channel coupling is exactly
> the same. For some reason there seems to be a crazy idea with a lot
> of people that mp3 joint stereo causes stereo image degradation.
> Imagine the horror if they would find out that Vorbis's advanced
> stereo modes are somewhat similar to intensity stereo. The WP expert
> audiophiles even heard stereo degradation in uncoupled Vorbis files.
> This is _all_ about psychology. (Guess that is why Vorbis has
> 'lossless stereo' instead of 'almost M/S stereo' :)
> 
> Some of the FAQ's of mp3 newsgroups even specifically _disrecommend_
> joint stereo 'becauses it is the prime cause of bad sounding mp3s'.
> Arghl. No wonder if you recommend BladeEnc...
> 
> Back to vorbis. Currently the stereo modes are not a black-and-white
> issue. Several stereo modes are used at once, depending on the
> frequencies that are being encoded and the actual audio content.
> The encoder intelligently switches between them.
> 
> If you are going to let the user switch between channel coupling
> modes, you can't depend on the user to understand these criteria
> (hell, even I am not sure about them). So what will be left is
> most likely a switch like
> 
> -mn   standard stereo coupling for selected bitrate
> -ml   lossless channel coupling
> -ms   seperate stereo (no channel coupling)
> 
> If you present this to the user, I am a whole lot will
> blindly select lossless coupling or seperate stereo. And end up
> with ogg's that sound like crap compared to what they would
> have gotten with the standard coupling.
> 
> Now, as I understand the current encoder, disabling the coupling
> will automatically give you higher bitrate oggs to compensate.
> That would be good, because it prevents users from shooting themselves
> in the foot with this. But it will cause problems because they
> end up with bigger files than they expected.
> 
> But this brings us back to the beginning. If you want to fiddle
> with this, you want to select a higher *bitrate* instead of
> fiddling with the encoding setup.
> 
> Perhaps there is a misunderstanding here about what the bitrate
> switches do.
> 
> Selecting a higher bitrate IS effectively picking an encoder
> setup with a higher lowpasss, less aggressive coupling and
> masking. INTERNALLY VORBIS DOES _NOT_ USE BITRATES (yet).
> 
> The only _good_ use of selecting a coupling mode that I can
> imagine so far is lossless coupling (or no coupling) for (e.g.)
> Dolby Surround encoded audio. So I'd propose a switch like
> 
> -md  Use this for Dolby Surround encoded audio
> 
> That way, you solve this case and prevent others from doing
> things they don't really want to be doing.
> 
> Now, perhaps God(*) has some good ideas about how to let the
> user pick their channel coupling modes _and_ prevent them
> from shooting themselves in the foot at the same time. If
> so, I'd love to hear about them.
> 
> 
> (*) Monty
> 
> -- 
> GCP
> 
> 
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----- Original Message -----
From: "Ross Levis" <ral@baycom.co.nz>
To: <vorbis@xiph.org>
Sent: Tuesday, September 04, 2001 7:14 AM
Subject: lowpass option (Was: RE: [vorbis] channel coupling in rc2)
> I would very much like a lowpass option because for FM radio broadcasting
I
> don't want to encode frequencies above 15khz.  I'm waiting for this
option
> before switching to ogg from mp3(lame).
What about lowpassing the files with an external app before feeding them
to oggenc?

I think that for example sox will handle this nicely.


--
GCP

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Ross Levis (ral@baycom.co.nz) wrote:
> > From: owner-vorbis@xiph.org [mailto:owner-vorbis@xiph.org]On Behalf Of
> > Gian-Carlo Pascutto
> > If you think the current lowpass is too low for your hearing then the
> > solution is more likely a higher *bitrate* than a higher lowpass.
Imagine a stereo that has only a volume knob.  If the music has not
enough bass, turn up the volume and you'll get more bass.  If the music
has not enough treble, turn up the volume and you'll get more treble.


-- 
Greg Wooledge                  |   "Truth belongs to everybody."
greg@wooledge.org              |    - The Red Hot Chili Peppers
http://wooledge.org/~greg/     |



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