[vorbis] Fwd: Re: Clarification on pshycho-acoustic in Vorbis (your non-MP3 guide)

[Rad]

Gian-Carlo,

Thanks for taking the time to review & comment on my guide.

I did my best to incorporate your comments - eliminating some text, adding
other parts, and including some new text.

Are you a developer for Ogg?

One question I have is what does this mean, and where/how does it apply?:

>If you want 160kbps VBR, pick gt1, else pick gt2. (gt2 also contains
> the 160kbps mode but I did not test it).
>
> You enable the 160kbps mode in gt1 by asking for a very high bitrate
> (-b 999).

I'm not familiar with gt1/gt2.

Rad
Laguna Beach, Ca.

----- Original Message -----
From: "Gian-Carlo Pascutto" <gcp at sjeng.org>
To: <vorbis at xiph.org>
Cc: <rad at radified.com>
Sent: Thursday, October 25, 2001 4:23 AM
Subject: Re: [vorbis] Fwd: Re: Clarification on pshycho-acoustic in Vorbis
(your non-MP3 guide)

>
> On Thu, 25 Oct 2001, Beni Cherniavksy wrote:
>
> > After reading http://mp3.radified.com/mp3.htm I sent Rad an
> > explanation of some things as I understand them.  He liked it and
> > posted it on his site (still unlinked, use the URL below).  Can
> > somebody with better understanding of psycho-acoustic terms and the
> > vorbis model check it and comment on it?  In particular I didn't know
> > how vorbis handles quantization noise.  If you reply with corrections,
> > CC: <Rad at radified.com>.
>
> About the 'noise':
>
> he probably originally heard about noise & tone masking.
>
> Tone masking is probably familiar to you, this is just when louder
> frequencies mask out adjacent quieter frequencies.
>
> Things aren't always that simple though. Think about what happens when you
> hit a cymbal. A cymbal doesn't really play a tone, it generates broadband
> noise. Noise masking basically determines how much extra noise the encoder
> can introduce in that noise without it being audible. This is generally
> more tricky than tone masking and one of the things that's improved a lot
> in RC3. (but RC2 did it still much better than LAME for example...LAME
> developers are now trying to imitate the Vorbis method ;)
>
> As for the original page, there are a few others things that raise my
> eyebrows.
>
> >
> While Lame offers what most agree to be the best MP3 encoding quality
> currently available, and the one being developed most aggressively, some
> claim that Liquid Audio, a proprietary encoding format, based on the AAC
> codec, is the *best* lossy encoder of them all, especially when bit-rates
> are taken into consideration.
> >
>
> a) Vorbis development is much more active than LAME development
> b) if you say AAC is the best, you at least need to give reasons,
> but you give none
>
> I find it funny MPC is critiqued for HF harshness, while it
> generally gives better quality than AAC (even at lower bitrates).
> For an objective test of MPC vs AAC vs OggRC2 @ 128kbps, take a look
> at http://www.ff123.net (also much info about MP3 encoders)
>
> >
> MPC's strength is the quality of the files it encodes, and the method
> (subband) it uses.
> >
>
> Subbanding is no guarantee at all for good quality. MP3 also uses
> subbanding for example.
>
> >
> Ogg Vorbis is a new lossy VBR encoder receiving much attention. The
> Vorbis.com site has been down a lot. I
> >
>
> Vorbis itself is not limited to VBR (although thats the only mode
> the encoder currently offers). The site was only down after it got
> swamped by the RC2 release. It's nearly never down now.
>
> >
> It has many cool features (such as bit-rate peeling and wavelets).
> >
>
> Vorbis 1.0 will have no wavelets. They _should_ be in later versions
> but I feel it too early to tout that as a cool feature. (Bitrate
> peeling is closer, and will work with Vorbis 1.0)
>
> >
> I've heard that some files encoded with Ogg exhibit harshness in the high
> frequencies, and others have problems with the bass.
> >
>
> The harshness in the high frequencies happens with the RC2 release
> at low bitrates.
> (not with previous versions, and also not with the tuned
> encoders and new experimental versions).
>
> Vorbis has _no_ known bass problems. Every report I have seen since
> RC2 has been bogus. If you still believe it has, send samples.
> We cannot fix a problem that does not exist.
>
> >
> Because Ogg is open source, it's possible for folks with coding know-how
> to modify (improve?) the program to their liking. That's what Garf did. I
> used to have a link to his page containing these files, but the link is
> no longer valid.
> >
>
> The link is: http://sjeng.org/ftp/vorbis
>
> If you want 160kbps VBR, pick gt1, else pick gt2. (gt2 also contains
> the 160kbps mode but I did not test it).
>
> You enable the 160kbps mode in gt1 by asking for a very high bitrate
> (-b 999).
>
> >
> It doesn't look like they ever plan to offer bit-rates exceeding 96kbps.
> I'm not sure why they would want to limit bit-rates, and not give control
of this to
> the user.
> >
>
> Simply because there is no use to the technique at bitrates higher
> than 96kbps. From 128kbps on the encoder can just store the info
> which MP3Pro would (often wrongly) predict.
>
> >
> Advanced Audio Coding (AAC). Whereas MP3 is based on MPEG-1 (layer 3), AAC
> is based on MPEG-2. MPEG-2 is what DVDs use (both audio & video), so it is
> an advanced, high-quality encoding format. Their catchy motto is Store
> less, hear more.
> >
>
> Nearly all DVD movies I have had in my hands so far used Dolby AC3,
> not AAC. AAC also exists in an MPEG-4 version AFAIK.
>
> There exists MPEG-2 extensions of MP3 too. There is no need to
> mention all this as it's both wrong and confuses matters.
>
> Why isn't the Liquid Audio section in the AAC section? It _is_ AAC
> after all, and the split up makes them look like something different.
>
>
>
> Perhaps there are corrections possible to my corrections. In
> that case, I'm sure someone on the list will point them out :)
>
> --
> GCP
>
>
>

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