Re: [Libmls0-developers] RE: libmls-0.3 released

[Daniel S. <ds...@ho...>]

>=20
>>I have two questions: what is FHT? Fast Hamahard Transform?
>=20
>=20
> Fast Hadamard Transform, I think.
>=20
>=20
>>Daniel: did libmls use FHT before and now uses FFT?
>=20
>=20
> Yes, I basically replaced the FHT transform routines from Anders Torger=
 with FFTW.
> I'm not sure if it would be more correct to call it DFT or FFT though, =
since it's not N^2 length.
> But FFTW must use some kind of FFT method anyway since it's so fast.
>=20

Well, I just realized I have studied this in a signal processing=20
course... I actually have access to very detailed theory on this=20
subject...:-)

>=20
> The above also means that the information in the README file is=20
 > longer correct. There is no mic calibration mode anymore, and
 > there must be a loop from the output to the left (reference
 > channel) and the right channel must be used for measurements.
 >

If this is the case we really need some updated documentation, could you=20
please patch the README and we will make an updated release.

> And then to my attachment:
> I have attached the loudspeaker library that I'm working on.
> I plan to put it on savannah.gnu.org or sourceforge soon, but I would l=
ike to have some comments on the code before I do that.
>

I will try to take a look at this and of course comment if I feel the=20
need to...

> My goal with this library, is that it, together with libmls, should be
> complete enough to replace CALSOD, MLSSA etc. with open source tools.
> I also want to keep it as portable as possible.
>=20

It's all about the GUI today, you know...:-)

Regards

Daniel Sundberg


> The intended audience is:
> Developers of measurement or loudspeaker software like e.g. gspeakers.
> Advanced users that would like complete freedom in choosing design meth=
odology.
>=20
> So it is both a library, to satisfy the first group.
> And a set of command line utilities using the above library, to satisfy=
 the second group.
>=20
> To make it both as portable and as easily scriptable/customizable as po=
ssible the command line utilities should only do one operation each and t=
he only thing requiring potentially hard to port or compile GUI code shou=
ld be the waveform viewer.
>=20
> Implemented at the moment is:
> *FRD/ZMA file I/O
> *Import of ddb speaker data base.
>   As generated and used by:
>   http://www.danbbs.dk/~ko/ubmodel.htm
> *Partial implementation of the loudspeaker model in:
>   http://www.hal-pc.org/~bwhitejr/btsmodel.zip
>   found here:
>   http://www.geocities.com/loudspeakerguru/Speaker_Design_Equations.htm=
l
> *Standard filter generator
> *Ladder filter simulator with file I/O
> *FRD waveform viewer
>=20
> The waveform viewer can use plotutils or gnuplot and it can display the=
 results from mra/sra.
> It doesn't require plotutils to compile and it should be very easy to p=
ort to other platforms or to embed in other applications.
>=20
> So most of the boring infrastructure things are at least usable and lot=
s of fun remains:
> Filter/box optimization, spice like simulator and other box types (tl, =
horn, etc.).
>=20
> When mra/sra has been updated with a bit more options (getopt) it would=
 be very easy to create a graphical front end that would just launch mra =
and pass the results to resgraph (the waveform viewer).
>=20
> There are some example scripts in the script directory,
> both for using plotutils and gnuplot.
>=20
> Regards,
> Daniel W
>=20
>=20
>>From: Daniel Sundberg <ds...@ho...>
>>Date: 2004/06/22 ti AM 11:11:57 GMT+02:00
>>To: lib...@li...
>>=C4mne: Re: [Libmls0-developers] RE: libmls-0.3 released
>>
>>Hi!
>>
>>I have two questions: what is FHT? Fast Hamahard Transform?
>>
>>Daniel: did libmls use FHT before and now uses FFT? I am afraid I have=20
>>not been looking very close at the source code lately (mostly since I d=
o=20
>>not own a decent measurement microphone).
>>
>>Also, when some of you start to work on a sample application it might b=
e=20
>>a good idea to create a separate module in the cvs or create a new proj=
ect.
>>
>>Regards
>>
>>Daniel Sundberg
>>
>>
>>dan...@br... wrote:
>>
>>>Hi Scott
>>>
>>>
>>>
>>>>A little while ago Daniel talked about replacing the FHT with another=
 scheme to generate the impulse response, which appears to have been done=
. Can you confirm that it is as fast as the FHT?
>>>
>>>
>>>I don't know if it's as fast as FHT, it's certainly fast enough for de=
sktop computers. I have no idea how they do it, but fftw doesn't seem to =
be that much slower for n^2-1 fft lengths than n^2 lengths.
>>>
>>>
>>>
>>>>Does the correlation still create a perfect unit response as it shoul=
d with the MLS?
>>>
>>>
>>>I'm not sure what you mean with a perfect unit response. But I'm sure =
the new scheme is much more accurate than the FHT. I have compared the re=
sults from the sweep mode with the MLS mode and they are the same.
>>>
>>>The problem with FHT MLS is that you assume that the soundcard doesn't=
 degrade the signal at all. It's in fact even more sensitive to this than=
 you might think. Even with an almost perfectly flat freqency response yo=
u will still not get good results with the FHT. I think the FHT should be=
 viewed as a last resort, only to be used when speed is top priority and =
not accuracy.
>>>Although some of the FHT problems could be solved with calibration I s=
till don't think you will get as good results as when you correlate in th=
e frequency domain. I'm not sure that the FHT errors are static enough to=
 be effectivly removed with calibration.
>>>
>>>
>>>
>>>>I must get started on a test/demo app.
>>>
>>>
>>>I have almost finished a waveform viewer/library that can be used from=
 other appplications, so you might want to wait for that.
>>>I will make it public as soon as I figure out where to put it.
>>>=20
>>>
>>>
>>>>One final thing. If we have upgraded the project name to level 1 then=
 I think we need to upgrade the major revision number to 1 as well. Perha=
ps 1.0.
>>>
>>>
>>>I agree on this, although I don't think we should go 1.0 until the lib=
rary is stable.
>>>
>>>/Daniel
>>>
>>>
>>>
>>>
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