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Topic: Monolithic transform codec? (Read 7330 times) previous topic - next topic
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Monolithic transform codec?

Hello,

Just one simple question for which I haven't been able to find an answer in the Internet... Being a "monolithic transform" codec means that Vorbis uses no subband coding?

Thank you.

Monolithic transform codec?

Reply #1 –
Correct. I think monolithic in this case means that there is only a single time-to-frequency transform, the MDCT, involved and that lossy and lossless coding is done entirely in the MDCT domain.

Chris

P.S.: To be absolutely accurate, the MDCT is also a subband filterbank, but I guess by "subband" you were referring to a low-frequency-resolution filterbank such as the QMF in MP3?
If I don't reply to your reply, it means I agree with you.

Monolithic transform codec?

Reply #2 –
Quote from: C.R.Helmrich on
P.S.: To be absolutely accurate, the MDCT is also a subband filterbank, but I guess by "subband" you were referring to a low-frequency-resolution filterbank such as the QMF in MP3?


Yes, that was what I meant. Thank you.

Monolithic transform codec?

Reply #3 –
Why does lossy audio codec usually use two transforms anyways?

-k

Monolithic transform codec?

Reply #4 –
Out of AAC, MP3, Musepack and Vorbis, only MP3 does, to the best of my knowledge. I dunno about AC3 and DTS. I think Speex doesn't either. That would tend to show that modern lossy audio doesn't use two transforms.

Monolithic transform codec?

Reply #5 –
Quote from: Canar on
Out of AAC, MP3, Musepack and Vorbis, only MP3 does, to the best of my knowledge. I dunno about AC3 and DTS. I think Speex doesn't either. That would tend to show that modern lossy audio doesn't use two transforms.


Doesn't MP3 only use the hybrid filterbank to maintain compatibility with Layer 1/2?

Monolithic transform codec?

Reply #6 –
Quote from: Canar on
Out of AAC, MP3, Musepack and Vorbis, only MP3 does, to the best of my knowledge. I dunno about AC3 and DTS. I think Speex doesn't either. That would tend to show that modern lossy audio doesn't use two transforms.

AC3 uses MDCT only, DTS is like MP2 which only use one filterbank splitting the spectrum into 32 bands and Speex doesn't use any of that (no "subband coder", no "transform coder").

The only codecs I know of that cascade two "transforms" is MP3 and Sony's Atrac.

Cheers,
SG

Monolithic transform codec?

Reply #7 –
Huh, I thought Speex was subband... Apparently not! *reads*

Thanks for the clarification, Sebastian.

Monolithic transform codec?

Reply #8 –
Quote from: knutinh on
Why does lossy audio codec usually use two transforms anyways?

-k



Mp3 uses one because the committee insisted that the filterbank for MP2 had to be included.

My own opinion is that it was an attempt to ensure someone's patent got used, as well as an attempt to make MP3 "too complicated', since "too complicated" was the whole excuse for throwing out ASPEC (which had entirely superior performace in terms of compression to start with) out.

What it did was ensure that MP3 would not be as good as it otherwise could be.  The combined time/frequency tradeoff is bad, annoying, and requires attention at encoding time that one would prefer to avoid.

The claim was that an ASPEC encoder would take 1 square inch of DSP.  Even at 1990 levels, the BS content of that is pretty hard to miss...
-----
J. D. (jj) Johnston

Monolithic transform codec?

Reply #9 –
Quote from: SebastianG on
Quote from: Canar on
Out of AAC, MP3, Musepack and Vorbis, only MP3 does, to the best of my knowledge. I dunno about AC3 and DTS. I think Speex doesn't either. That would tend to show that modern lossy audio doesn't use two transforms.

AC3 uses MDCT only, DTS is like MP2 which only use one filterbank splitting the spectrum into 32 bands and Speex doesn't use any of that (no "subband coder", no "transform coder").

The only codecs I know of that cascade two "transforms" is MP3 and Sony's Atrac.

Cheers,
SG



SG, there are some omissions in your DTS comments, but I don't think that's the subject of this particular thread.

However, I must also point out that, in relevance to this thread, the MPEG-2 AAC SSR Profile also uses a hybrid filterbank using a 4 band PQMF and 256 pt MDCT's.

I'm not aware of it being applied anywhere.
-----
J. D. (jj) Johnston

Monolithic transform codec?

Reply #10 –
Quote from: SebastianG on
Quote from: Canar on
Out of AAC, MP3, Musepack and Vorbis, only MP3 does, to the best of my knowledge. I dunno about AC3 and DTS. I think Speex doesn't either. That would tend to show that modern lossy audio doesn't use two transforms.

AC3 uses MDCT only, DTS is like MP2 which only use one filterbank splitting the spectrum into 32 bands and Speex doesn't use any of that (no "subband coder", no "transform coder").

The only codecs I know of that cascade two "transforms" is MP3 and Sony's Atrac.

Cheers,
SG


All three atrac lossy codecs use a hybrid MDCT subband transform, so theres at least 4 (semi) widely used hybrid codecs out there.