I'm not sure I buy the argument that averaging results over many different samples will improve the performance of the EAQUAL algorithm.

For example, suppose that EAQUAL in general fails to properly penalize pre-echo artifacts (which seems to be a plausible hypothesis). Then, averaging over many different samples won't necessarily compensate for this failing. Yes the results will be more reliable, but they won't be more valid.

ff123

Alexander,

I wonder why a test sample for EAQUAL should be at least 10 to 20 sec.?

Hi,
Of course you are correct. EAQUAL in its current version is not very sensitive regarding pre-echo artifacts.
Let me formulate it in this way: the algorithm's results will be more valid within the limitations of the algorithm. This was more or less proved, see Treurniet et al., Evaluation of the ITU-R Objective Audio Measurement Tool, Journal of the AES No.48, 2000

Alexander

For the analysis, a few seconds at beginning and end do not influence the result. This should be because the listeners are often less concentrated or may think artefacts like clicks etc are due to their playing equipment which is starting or stopping. Don't know if this is true or not. Perhaps there is another explanation too, but standards don't explain anything.

Alexander

There was another objective tool based on the work of Frank Baumgarte, which EarGuy implemented and played with in the r3mix forums. It seemed to consistently show bad results at the beginning of an mp3 file. I don't know of any listening tests which confirm this effect, or what could explain it, but in the files I prepare for listening tests, I sidestep this problem (if it is a real effect) by duplicating the entire sample, and then by cutting it in half (choosing the second half, of course) for the final file.

[tangent]Interestingly, Fraunhofer's mp3enc codec will produce different artifacting depending on what signal went before, so it can be tricky to capture bad sections for this codec by excerpting sections of a song, and the method I use above will yield different results for mp3enc than just using the straight sample.[/tangent]

I also found early on that playing files which don't begin or end with silence can cause clicks initially upon playback. I avoid this problem by adding some silence before and after the sample.

ff123

Just added --r3mix to my test results.

Strange things happening on deerhunter.wav (sample from ff123). Lame --r3mix with only 113 kb/s is better than --alt-preset (fast) standard (154 and 163 kb/s). Also Psytel aacenc -normal (153 kb/s) is better than -extreme (183 kb/s). :confused:

Link: http://home.wanadoo.nl/~w.speek/eaqual.htm

ITU-R BS.1387 also has "advanced" ear model, which is implemented in Opticom OPERA software,

here is what AES paper #4931 (regarding to PEAQ) says about "advanced" model:



Andree Buschmann told me in some mail that he wasn't satisfied with PEAQ tool used in debugging of the AAC codec in Bosch - tool missed some important artifacts in fatboy.wav - but that's ok from my point of view - BS.1387 has its application, it is good to some degree, but it can't replace audiophile's ear

Oops, here I was not correct. It is some time ago I implemented this and kept it wrong in mind, perhaps I read something about this. It is only .5 seconds at beginning and end that don't influence the result. So, the minimum filesize would reduce a little bit.

Alexander

Im in the middle of some testing, Id just like to confirm that 1024 is the correct offset for Psytel AAC, I`ll post the results later.

Thanks,
Alex

It depends on what decoder you use. With the newest FAAD decoder dated 2002-01-05 the offset is 0.

so with 2002-01-05 its 0 and pre-2002-01-05 its 1024?
I just want to confirm this, Im getting some supprising results for Psytel, the results for other codecs are what I would expect.
I will post my results shortly but Id like to make sure they will be accurate.

So if I wanted to test a LAME encoded and decoded file I shouldn't set any offset?


Jan.

yes so long as you use lame.exe --decode then there is no offset, Im not sure about any other decoders.

With FAAD 2002-01-05 the offset is 0
With FAAD 2001-06-06 the offset is 1024
With other FAAD I don't know. But you can easily do the test with castanets and CoolEdit (or any other wave editor) that Ivan described at the beginning of this thread.



The LAME decoder corrects the offset. So if you decode a LAME MP3 file with LAME the offset is 0. If you use another decoder with no offset correction the offset will probably be 1105.

I downloaded the 2002-01-05 FAAD and the results were ok, although Psytel AAC still performed worse than Lame in the test that I did.

Yeah, I hope Todd (Earguy) can come up with improved Baumgarte's digital ear model.

Quoting his email: "I discovered a major mistake that I made. I can't read German, so I was using online translators to translate Frank's disertation to English. In his disertation, he gives two different sets of model parameters to use. I didn't understand what the difference was between the two until now (online translators have improved in the last two years). And of course I was using the wrong set of parameters! So the previous results are in error. I will definitely have something to show early next year so watch the forums for my posts."

I hope that correctly working Baumgarte's digital ear will be better than PEAQ ITU-R BS.1387 basic model.

Speaking about EAQUAL (PEAQ) psychoacoustic model, I had finally taken a look in the recommendation (psychoacoustic model description) and I must say that it is based on more advanced model than ISO Psychoacoustic Model II - I also know that one state-of-the-art compressor (I won't tell which !) is using many of properties from this model.

Non-linear Spreading function used in this model is described in Baumgarte's "Application of non-linear psychoacoustic model in ISO Layer III codec" (used to avoid tonality estimation problems). Also it uses temporal masking.

Its only weakness is 2048 sample length of the analysis window.

Ivan, could you explain this a little bit more?

Here's how imagine things:
A = reference file
B = test file
x = window where the attack/transient is (or begins)

I suppose EAQUAL compares each window of B to the corresponding window of A. So when there's pre-echo in B either Bx or Bx-1 will not be the same as Ax or Ax-1. So EAQUAL will detect the pre-echo. But I guess things don't work as I imagine?

Basically, the tool sees all audio in 20ms chunks in the frequency domain. This means that it will not clearly see any distortion smaller than 20ms in the temporal domain, because the error from the preecho is 'spread out' over a 20ms timeframe.

The preecho is audible because it is a relatively big distortion over a very small time interval. The tool will not see the difference between it and a very small distortion over a larger interval, which would be inaudible.

2048 samples is about _twice_ the size of an MP3 _large_ block btw. This would mean it's really completely blind to any temporal artifact.

(Disclaimer: Not sure this is all 100% correct, and I hope those that know will correct the mistakes)

--
GCP

Imagine this situation:

Divide the 2048 in 8 blocks of 256 time-domain samples (128 coefficients)

Now, inject the noise in each of the 8 blocks, say 10 dB - in all cases tool with 2048 sample window will detect it as the same increase of noise, but it can't guess in what segment problem occured.

2048 sample (1024 coefficient) window is standard MPEG AAC "LONG" window size. Because it leads to serious pre-echo problems, smaller window of 256 samples is employed if the signal conditions require it.

Fraunhofer aac demo v2.2?


bye, dB

Could someone test the GOGO NoCoda with competitive bitrate VBR settings?

hello all
have anybody have the free source code for ITU_R B.1387 or link to it( http://sourceforge.net/projects/eaqual/ this link does not contains any code.)
If i have to purchase the eaqual source code what is the price and source for it

u can contact me at

Direct download from Mitiok's site: http://home.pi.be/~mk442837/EAQUAL.tar.gz

thanks speek
the code here is building and running fine
thanks alot:)

or mp3-tech.org

which version of EAQUAL is the latest available for download and where?

http://rarewares.org/others.html

thx.