Some thoughts for the new year: 1) MDCT is good for image coding 2) image coding and audio coding are two very different things 3) combine 1 and 2 4) if a psycho model is good, after leaving out what it tells you you can without hurting quality, applying the same model should yield the same results as you got before 5) from 4: decode -> encode -> decode should result in (almost) the same stream. Dagdag, Segher --- >8 ---- List archives: http://www.xiph.org/archives/ Ogg project homepage: http://www.xiph.org/ogg/ To unsubscribe from this list, send a message to 'vorbis-dev-request@xiph.org' containing only the word 'unsubscribe' in the body. No subject is needed. Unsubscribe messages sent to the list will be ignored/filtered.
On Wed, Dec 27, 2000 at 04:41:55AM +0100, Segher Boessenkool wrote:> 1) MDCT is good for image coding > 2) image coding and audio coding are two very different things > 3) combine 1 and 2It follows that MDCT is good for many differnt tasks. No? :)> 4) if a psycho model is good, after leaving out what it tells you > you can without hurting quality, applying the same model should > yield the same results as you got before > 5) from 4: decode -> encode -> decode should result in (almost) the > same stream.Only if the system is stable. With most MP3 encoders, the stupid subbanded bit allocation routiene is greatly affected by the quantization noise from prior encoding runs. Also, things like the mid-side selection may be triggered by quantization noise. A while back, I did some testing and found Vorbis to be fairly stable through multiple encode iterations, more so then the mp3 encoders I tested. I suspect that current and future fine tuning of things like block switching might, however, make the encoder less stable in this regard. Whats more intresting is that the framing used in vorbis will allow many types of editing without a complete decode/recode cycle. --- >8 ---- List archives: http://www.xiph.org/archives/ Ogg project homepage: http://www.xiph.org/ogg/ To unsubscribe from this list, send a message to 'vorbis-dev-request@xiph.org' containing only the word 'unsubscribe' in the body. No subject is needed. Unsubscribe messages sent to the list will be ignored/filtered.
On Wed, Dec 27, 2000 at 04:41:55AM +0100, Segher Boessenkool wrote:> Some thoughts for the new year: > > 1) MDCT is good for image codingActually, I disagree already ;-) Monty --- >8 ---- List archives: http://www.xiph.org/archives/ Ogg project homepage: http://www.xiph.org/ogg/ To unsubscribe from this list, send a message to 'vorbis-dev-request@xiph.org' containing only the word 'unsubscribe' in the body. No subject is needed. Unsubscribe messages sent to the list will be ignored/filtered.
xiphmont@xiph.org (Monty) writes:> On Wed, Dec 27, 2000 at 05:16:26AM +0100, Segher Boessenkool wrote: > > The problem is, audio needs shorter windows at higher frequencies > > (and *really* large windows at low frequencies, to get good results). > > I do agree with this observation. :-)The obvious idiot/newbie followup is: Well, then would it be possible and useful to split the signal into a couple of frequency bands and encode them each with differently sized blocks? --- >8 ---- List archives: http://www.xiph.org/archives/ Ogg project homepage: http://www.xiph.org/ogg/ To unsubscribe from this list, send a message to 'vorbis-dev-request@xiph.org' containing only the word 'unsubscribe' in the body. No subject is needed. Unsubscribe messages sent to the list will be ignored/filtered.
Segher Boessenkool <segher@wanadoo.nl> writes:> Sure. But we need to find a good, non-patented, transform that does exactly > what we want, and some changes to the psycha model to go with it. > > Are you scared yet?No, because I don't really understand what's going on (yet). :-) --Mike -- [O]ne of the features of the Internet [...] is that small groups of people can greatly disturb large organizations. --Charles C. Mann --- >8 ---- List archives: http://www.xiph.org/archives/ Ogg project homepage: http://www.xiph.org/ogg/ To unsubscribe from this list, send a message to 'vorbis-dev-request@xiph.org' containing only the word 'unsubscribe' in the body. No subject is needed. Unsubscribe messages sent to the list will be ignored/filtered.